Jetting help

[zrpilot]

Originally posted by richards
Let's have a discussion about how to tune main jets...

I was actually thinking of starting a thread regarding this very subject. Let me first start by saying I’m NOT an expert on this, but I have some dyno evidence and experiences I would like to share.
First some basics:
1) Every bike is different
2) Temperatures, humidity, barometric pressure, and elevation ALL have an effect on jetting
3) Jetting TAKES TRIAL AND ERROR, no one can prescribe the perfect jetting for you, you HAVE to experiment and find what works for your bike.
4) If during the jetting/tuning process you have made a number of adjustments (especially main jet or needle clip) to the carburetor and the engine has not changed. There is a strong possibility that something other than carburetion jetting is causing your engine to perform incorrectly. Jetting is a constant. When adjustments are made to a machine with all components working properly the engine will respond in some way. Depending on the adjustment made the machine will either run better or worse, but there is almost always some form of change. When changes are made without any response it is a sign of other problems. For example float level needs to be correct as it affects jetting and tuning if wrong.

Originally posted by richards
Used to be you could read spark plugs but that was iffy back in the day and it is worse now as newer gasoline additives can affect plug color.


Good point. I often want to chime in when I see posts about a fella that rode his quad for an hour and pulls the plug, looking at the color for jetting. This is not an effective way to judge jetting. It COULD be, but there is a specific method of doing this that involves looking at the insulator on the inside of the plug which almost always requires cutting the plug apart to see.
OK so lets talk about the different circuits and what they do, see picture below:

http://i94.photobucket.com/albums/l97/zrpilot/calchart.gif

Fuel SCREW (Pilot screw in diagram below): The fuel screw is a small slotted brass adjustment screw located on the engine side (closest to the motor) of the carburetor. This screw is a fine-tuning adjustment designed to allow the carburetor to be slightly adjusted for variances in atmospheric conditions. The fuel screw works with the pilot/slow speed system of the carburetor, mainly affecting the engines initial starting, idling and initial power delivery. Proper adjustment of the fuel screw can offer direct feedback on the necessary setting required for the pilot jet. The fuel screw is adjusted in a rather straightforward manor.

The ideal procedure for setting the screw in the correct position is to warm up your ATV engine to the proper operating temperature. Then turn the idle up so it is idling about 500 RPM’s higher than normal. Next turn the fuel screw all the way in until it lightly bottoms out, once bottomed out slowly back the screw out a ¼ turn at a time (give the engine 10-15 seconds between each ¼ turn of the screw, to allow the engine to catch up with the adjustments). Continue backing the fuel screw out until the engine idles at its highest RPM. The preferred setting window is between 1 and 2 turns. If the engine idles at its highest RPM from 0-1 turns out this means the pilot setting is on the RICH side and a smaller pilot jet should be installed. If the engine idles at its highest RPM at over 3 turns out, this means the pilot setting is on the LEAN side and a larger pilot jet should be installed.

If you get no RPM fluctuation when adjusting the fuel screw there is a very realistic chance that there is something clogging the pilot/slow speed system. Clean the system thoroughly with contact cleaner and blow out with compressed air. Carburetor must be disassembled.

PILOT JET (Slow Jet in Diagram below): The pilot jet is a brass jet located inside the float bowl next to the needle jet/main jet location. The pilot jet meters the fuel required for engine starting, idling and the initial throttle opening 0-1/8. A lean pilot jet setting will cause your engine to surge at very low RPM’s, bog or cut-out when the throttle is opened quickly and have trouble idling down. A rich pilot setting will result in hard starting, plug fouling at low RPM’s, sputtering as the throttle is cracked opened. The pilot jet is not difficult to set. With proper fuel screw adjustment fine-tuning should be painless. Once set the pilot jet is not terribly sensitive. If adjusting the pilot jet gives inconsistent feedback, or does unexplainable things. Check and clean out the pilot/slow speed system thoroughly with contact cleaner and blow out with compressed air. Pilot jet sizes are numbered in the following pattern; #42, #45, #48, #50, #52, #55, #58, #60 etc. repeating the pattern.

NEEDLE: The jet needle is the most important component in determining your carburetors jetting. The needle functions have a large effect on the carburetors jetting from ¼ to ¾ throttle.

The safest way to set the clip position is to richen up the clip position setting until the machine loses a little power (feels lazy/unresponsive) then lean it back one position. Ideally you like to run the needle setting in either the 3rd or 4th clip position, if possible. The needle clip jetting is especially critical because on average more time is spent in the midrange than any other part of the throttle. Most machines pull very hard in the midrange, putting quite a load on the engine.

MAIN JET: The main jet affects the jetting in the upper quarter of the throttle position. Coming into play at ¾ throttle on through to full open throttle. Even though most people relate the main jet to their carburetor in general. The main jet is only responsible for the last ¼ of the jetting. The main jet does not affect the jetting for starting and idling. It plays no part on low RPM or mid RPM jetting either. The main jet is very important to your machines overall tuning, but should never be over emphasized at the expense of needle tuning or other facets of your carburetion tuning.

Start with the biggest numbered main jet and run at wide open throttle, the engine should stumble at wide open throttle. Install the next smaller size until the stumble is gone. Once the main jet is correct re-adjust the pilot screw first and the pilot(or slow) jet if needed until proper idle is obtained.
This were a timed wide open throttle run could indicate proper jetting.


http://i94.photobucket.com/albums/l97/zrpilot/Jets.jpg


Originally posted by richards
I believe one guy posted dyno results showing a couple of HP difference between two adjacent main sizes.

Actually that was me and you’re a little off. I showed back-to-back dyno runs with a 6 point main jet change and it did not make a significant difference in power output.

So how do jetting changes affect engine performance?

Here is a 6 point main jet change makes very little difference in power (assuming the jetting is close to begin with, rather a more significant change in the AF ratio. I went from a 152 to a 158 main. No a big power difference, but look at the AF. The 152, for me, was a little lean.

But I would venture a guess as to say the 400EX would be JUST fine running this lean (as long as it did NOT detonate!!!!)

http://i94.photobucket.com/albums/l97/zrpilot/6_point_main_change.jpg

Now here is a graph showing what the needle change can do... notice how the whole a/f curve changes across the entire middle RPM range...also notice how I gained nice power in the mid-range yet lost it on the top. A main jet change would take care of this.

Note there was not enough warm up run once the needle was changed, so the picture maybe a little different after some warmup.

http://i94.photobucket.com/albums/l97/zrpilot/needle_change.jpg

When I started the dyno run, I was jetted a follows:

Main 175
Needle: #3
Pilot #52

Ended up at:

Main 158
Needle: #4
Pilot #52

Interestingly, I thought my 400 ran pretty good before on the larger jets. Of course it ran much better after!!!!

Notice the power and AF changes. This is why a dyno can be an invaluable tool for tunning!!!

Below is the begining run and final run.

http://i94.photobucket.com/albums/l97/zrpilot/begging_to_end_jetting.jpg

What does warming up have to? Here are a few runs with NO jetting changes, just successive pulls, notice the change. Is it warm-up? I think so...

Note all these runs were done in a 2 minute time span... no changes....

http://i94.photobucket.com/albums/l97/zrpilot/warm-up.jpg




Obviously the best way to get jetting right on is to put it on the dyno, but I think that someone can get the jetting close by listening and watching how the quad performs while riding. Make jetting changes methodically one step at a time. I hope this helps people understand jetting a little more

Comments welcome!

[tri5ron]

I've been hoping you'd do something like this.
I think it will be a big help to those of us who could use some help in learning proper jetting.
Thanks, and good job.

[DirtMonkey]

Sticky!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[Wheelie]

Something else to add to this.

It seems as though a lot of people try to tune their machine in neutral by revving it. In turn they often mistake a flat spot when stabbing the throttle as not being tuned properly.


This is NOT the proper way to tune. Tune the machine in gear, under a load in real world riding conditions--NOT in your garage or truck.

[zrpilot]

Originally posted by Wheelie
Something else to add to this.

It seems as though a lot of people try to tune their machine in neutral by revving it. In turn they often mistake a flat spot when stabbing the throttle as not being tuned properly.


This is NOT the proper way to tune. Tune the machine in gear, under a load in real world riding conditions--NOT in your garage or truck.

Good point

[RaginRedneck]

WOW. ZRPilot is the MAN!!

Nicely done. Thanks for taking the time to do this.

STICKY THIS THREAD!!!

[richards]

Great stuff, thanks zrpilot.

I'll add a bit of backround on what is going on in the carb, may help people think through what they are adjusting.

The chart zrpilot posted showing Effectiveness vs. Throttle Opening is showing what jetting changes affect what throttle openings. The 3 main things we are tuning on our carbs are the pilot circuit, the needle position, and the main jet.

In the chart "Air Screw, Slow Jet" is the equivalent to our pilot circuit. On most 2 strokes the adjuster is called the "air screw" because it is controlling the amount of air coming into the pilot circuit. On most 4 strokes it is called the "fuel screw" because it is controlling the amount of fuel coming into the pilot circuit. Note there are exceptions, so always double check the carb you are working with. Our Keihin carbs use fuel screws. In the chart the "Slow Jet" is what we normally call the pilot jet.

The fuel screw and the pilot jet work together. The pilot jet controls the max amount of fuel that can flow through the pilot circuit. Larger numbers mean a larger hole in the jet and thus a higher max fuel flow. The fuel screw fine-tunes the fuel flow in the pilot circuit. When it is fully screwed in it closes the circuit and no fuel can flow. When it is fully screwed out it will allow the max fuel flow allowed by the pilot jet. Fully screwed out is usually in the 3-4 turn range, backing out any further than that will not change anything as the circuit is fully open and limited by the size of the pilot jet. This is why you should switch to a larger pilot once you are over 3 turns out when trying to find the sweet spot. You can go up 1 size on the pilot and then start tuning again around 1 turn out on the fuel screw.

The needle and the main jet work together in a similar way to form the high speed circuit in the carb. The main jet, like the pilot, controls the max amount of fuel that will flow through the high speed circuit. The needle controls how much fuel can come through the circuit at a given throttle opening. If you look closely at a needle you will notice is is tapered. Looking at the carb and moving the slide up/down you can see the needle goes in and out of a tube at the bottom of the carb bore. The main jet is attached to the bottom of that tube. So when the slide is open and the needle comes out of the tube the circuit will flow the max fuel allowed by the main jet size. As the throttle is closed the needle starts blocking the hole in the tube thus reducing the fuel flow.

When you "raise the needle" or "drop the clip" you are moving the needle up in relation to that tube. So at any given carb opening a bit more fuel will flow. Thus raising the needle richens the mixture. The chart shows the range that the clip position affects - about 1/8 to 3/4 throttle. So clip/needle position will not affect your idle (that's the pilot circuit) nor will it affect WOT (that's the main jet size).

Hopefully now you can see what is going on and have a feel for what you are doing when making jetting changes.
[list=1]
select pilot size
adjust fuel screw
repeat 1 and 2 until you find a good combination for idle and initial opening of the throttle
select a main size
test at WOT
repeat 4 and 5 until you are happy with the mixture at WOT
adjust the needle clip position
test for clean running through the 1/8 - 3/4 throttle range
repeat 7 and 8 until you are happy with the mid range throttle response
[/list=1]

One thing not discussed much for the 400ex is the needle taper. Probably because the stock taper in the stock carb and the 450R carb seems to work pretty well. 4 strokes are more forgiving on taper than 2 strokes in general. If you look at a discussion on 2 stroke jetting you will see a lot more talk about which needle taper to use. The needle taper is just the shape of the tapered section of the needle. It can taper slowly from the tip to the full thickness of the needle or more quickly and this affects the amount of fuel that flows through the circuit at a given throttle opening. Some needles do not have a constant taper, the angle changes one or more times along the length of the needle.

[Wheelie]

It would make a great sticky, especially with all the tuning/jetting questions and misconceptions.

[F150 Rider]

This Definately needs to be a STICKY! I am getting ready to rejet my 400ex and this just answered most if not all of my questions! Thanks Fellows!

[brodzowski]

PLEASE sticky this before it gets lost. Bump ttt. And thanks to ZR and the other fellas for putting some great information together!

[buster024]

I'm just going to bump this to the top until it stays there.

Great write up. It makes me want to go out and re-jet right now. Nice work ZR.

[zrpilot]

Sticky?

[Wheelie]

Mission accomplished. Now if someone would sticky my 450R brake upgrade thread, I'd be tickled.

[KrackerG]

good info here...tore into my carb over the weekend, turns out i still have the stock jets. anyone want to help me get to a good starting point?

i have:
400ex (440 kit)
stock ex carb
full exhaust
K&N cone, outwears airbox lid
93 octane gas

i am in the mid atlantic, near sea level. i run mostly on trails.

[ZJTurbo]

Whats up guys need some help. I have HMF Slip on, uni filter no box, hot cams stage 2 and a 450r carb. I am at sea level. I have a 42 pilot and 172 main it pops on decel ans is a little white? I was thinking 178? I also need help with my needle and an explanation on where in the power band and the needle jet plays a roll?

[Wheelie]

Popping on decel indicates a lean pilot circut. Install a 45 or 48 pilot and leave the 172 in place for now.

The needle affects 1/4-3/4 throttle position. I tune the needle on my machine by riding at half throttle for awhile.

Read page 1 of this thread for a good chart of every circuit and their role.


KrackerG--
Start at a 42 pilot, 4th notch from the top
on needle and 172-175 main.

[BikeSwimLaugh]

Agreed....GREAT write-up!!! :)

I've got a pretty much stock 400EX but I just installed the K&N air filter and an HMF slip-on. The place that sold me the air-filter & exhaust also sent me a new jet, a 152 The guy assured me it was tested and it's proper...so I hope so. I'll give it a try later when I get a new front tire and can head out again.

Question, something many people would likely want to know. I used a write-up on this forum to do the re-jetting...it had 20+ steps involving removing the seat, gas tank, front fenders, air-box, etc, etc. Did I REALLY have to do all that just to change the main jet? A few people told me I should be able to loosen the band clamps fore & aft the carb and just turn it sideways enough to loosen the 17mm drain bolt and access/change the main jet from there.....is this true or is all that disassembly/reassembly required? Short-cuts appreciated :D

[RaginRedneck]

You CAN rotate the carb to get to the main jet without removing fenders and tank, but it gets a little cramped. Removing that stuff only takes a few minutes.

If you need to replace or adjust the needle, you need the carb off.

[BikeSwimLaugh]

Originally posted by RaginRedneck
You CAN rotate the carb to get to the main jet without removing fenders and tank, but it gets a little cramped. Removing that stuff only takes a few minutes.

I dunno.....the seat, the tank, the fenders, air-box....took me a while, BUT that was the first time I did it. I think you're right, I could probably do the whole thing all over again in a matter or 10 minutes...now that I know exactly where everything goes and how it goes together.

I had one nasty problem. When I went to remove the band clamp between the carb and intake maifold, the phillip's head just stripped....maybe they lock-tite'd it at the factory. I had to take a drill and drill-out the head until the band popped. Luckily, I had a bolt with the right length & thread to replace it. It's always nice when things disassemble and reassemble nicely...but there's always a few challenges along the way. Very rewarding and fun when it all works together...extremely frustrating when it doesn't. But you know the saying: nothing in life that's worth having comes easily.

I hope changing the get from 148 to 152 is all it'll take to dial a stock 400Ex back to "tune" after adding an HMF exhaust and K&N air-filter.

[RaginRedneck]

You should be close with that setup. I didn't remove my airbox to get the carb out.

Additionally, A little time saving technique was after I put the jet in I just reinstalled the fuel tank and carb. I left the fenders and seat off and did my hot laps that way to check the plug. Luckily I nailed the jet size and just had to screw with the air screw to get it dialed in.

Good luck.

[BikeSwimLaugh]

To review: stock 400EX HMF slip-on exhaust and K&N air-filter and I just re-jetted from the stock 148 to a 152

Welp....just fired it up and took it for a test spin. Fires-up just fine, idles really nice. Low-end & mid have a really smooth & nice pull...BIG-TIME difference from stock. Everything feels great with a noticable improvement...up until I go WOT and try to wind it out.

I put it in 2nd and pulled the throttle wide-open...it went from idle all the way to about 85% wound-out, but then it starts to hesitate & "stumble" and it won't wind-out all the way. Again, the low & mid are great, but once I get towards the top-end it just doesn't want to wind out. I'm guessing lack of fuel and I need to jet-up to a higher number????

Hmmmm....


Originally posted by zrpilot
Start with the biggest numbered main jet and run at wide open throttle, the engine should stumble at wide open throttle. Install the next smaller size until the stumble is gone.

Reading this, it sounds like I've got to large a jet? cause I still have some "stumble" at WOT. Ya know, the air-filter instructions say I should remove the air-box lid. I did not do this yet, maybe that would make the difference? I'm still pulling air through that elongated snorkel...removing the lid should provide more air, so if I'm over-jetted and running rich, the additional air (or ease of air, eh?) might compensate for this. Am I on the right trail??

Dude....THANKS! :D

[richards]

Originally posted by BikeSwimLaugh
To review: stock 400EX HMF slip-on exhaust and K&N air-filter and I just re-jetted from the stock 148 to a 152
...
it went from idle all the way to about 85% wound-out, but then it starts to hesitate and it won't wind-out all the way. Again, the low & mid are great, but once I get into the top-end it just doesn't want to pull all the way. I'm guessing lack of fuel and I need to jet-up to a higher number?

Some help please.... :)

Yes I think you are on the right track considering a different main. I would try one size larger (154) to see if it helps. If not then go one size smaller (150) and see if that helps. Whichever direction makes it better, try going one or two more sizes in that direction 'till you've found the one that runs best at WOT.

You should be able to get Keihin mains for a few bucks a piece at any well-stocked motorcycle shop. Notice I said _shop_ not dealer. You want to find a place that caters to racers and modified bikes, if they do that kind of work they will have a large stock of jets.

[BikeSwimLaugh]

Thanks for the lickety-split reply. I've edited my post after re-reading from page 1, please check it out.

The instructions say to go with a big number jet until the engine stumbles, then size down. Since I'm already stumbling, I'd figure I need to go to 150....but the guy at the parts place was so certain the 152 was tuned for my pipe/air-filter.

Well, as I wrote, I'm still running my air-box lid and this restrictive issue is likely the culprit. No doubt I should remove the air-box lid and check it all out again. Pulling air through a 2-foot elongated 1.75-inch tube is a whole lot different then having the entire top of the air-box wide-open! Best I try that before even thinking of tinkering with the jet again.

But yeah, for the price I'd pick-up a 150 and 154 (one higher, one lower) and see what that does.

I've got to say, changing the air-filter and exhaust really does make a big difference. Love the sound too! :D

It's all fun so long as 1) Nobody gets hurt, 2) no crashes, 3) No flat tires and 4) Everything reassembles with no extra parts and things go together right. :D

[RaginRedneck]

I would start with the 155. I've got a similar setup to you, K&N, Air lid on, Slip-on. The only other thing that I have is a CDI Box that advances the timing. I ride at about 600ft -1000ft. and I'm at a 155 main, 2 1/4 turns out on the mix screw.

[BikeSwimLaugh]

Thanks for the tip!

What are your thoughts on the air-box? I'm not sure I want to run with absolutely no lid at all...so I was considering getting an aftermarket lid with a built-in filter or just mod'ing the stock one myself.

I'm riding anywhere from 1,500 to 5,200-feet....probably averaging about 2,000....any thoughts on how to account for that on the main jet?

The CDI ignition box...what's that mod all about? I've only heard vague references to it...what's the pro's, con's, etc. Thanks!

[RaginRedneck]

As far as the Air Box, it pretty much all depends on what conditions you ride in.

As far as the altitude, someone else on the board is probably more knowledgeable on that subject. I believe that the higher the altitude the lower the main due to the reduction in air mass, but I'm not sure at what level that starts.

The CDI box is basically the brain. On my '07 its located under the hood behind the headlight. You unplug the stock one and plug in the new one. The moose CDI box I have advanced the timing, increased the spark intensity, increased the rev limiter and removed the rev limiter in reverse.

It was right around $120 for the CDI box w/ a complete Jet kit. So I think it was well worth it.

[KrackerG]

Originally posted by Wheelie
... KrackerG--
Start at a 42 pilot, 4th notch from the top
on needle and 172-175 main.

thanks Weelie, i will start out with the 175 main and 42 pilot. most of the others i've spoke with said to start around the same place.

[Tofu.Man]

400ex with the followin Mods,

Curtis Sparks X6 exhaust
Curtis Sparks advance key.

Im at 390ft elevation.

My jetting is a 42 pilot and a 165 main, stock needle setting and 2 turns out on the fuel screw. All keihin jets BTW.

I dont know anyone else with similar mods. I would just like to know where they are at and what jets they are using.

[BEAVER.989]

There is some great information here. I do have a question, though. Why is it that the needle is considered the most important part of the equation, yet it gets paid so little attention?

I see a lot of jetting recommendations involving a new main and piolot, but stock needle position. These recommendations come from both forum members and pipe manufacturers(Curtis Sparks, for example)...

Is it because of the fact that when you adjust both the main and pilot that it usually has a big enough effect on the needle? Or is it just that most people don't understand enough about the needle to mess with it?

[BikeSwimLaugh]

Beave....

That's a GREAT question. I have to admit, when they start talking about 2nd or 3rd position on "the clip", I have NO IDEA to which part they are referring. I'm sure it's simple, I've just not seen any pics or diagrams showing this particular area/part.

I really enjoy answering questions and helping people....but I have to digress...I just don't know about this area, let's hope someone else does!

[zrpilot]

Originally posted by BEAVER.989
There is some great information here. I do have a question, though. Why is it that the needle is considered the most important part of the equation, yet it gets paid so little attention?

I see a lot of jetting recommendations involving a new main and piolot, but stock needle position. These recommendations come from both forum members and pipe manufacturers(Curtis Sparks, for example)...

Is it because of the fact that when you adjust both the main and pilot that it usually has a big enough effect on the needle? Or is it just that most people don't understand enough about the needle to mess with it?

The needle is probably the most complicated and difficult jetting variable to deal because it is made up of three things, diameter, taper, and clip position. IMO, the only way to effectively fine tune a needle is on a dyno with a wide band O2 sensor.

DIAMETER: The needle diameter controls the jetting just above the pilot jet, right as the engine begins to pull. The needle diameter is felt in the ¼ throttle range. A bigger diameter needle makes this range leaner, whereby a smaller diameter needle makes this range richer.

TAPER: The needle taper is the angle of the needle at its lower half. The taper works the transition between the mid-range and full throttle/main jet (¾ throttle position). The taper is the least sensitive function of the needle. Changes in the taper have very mild subtle changes in the jetting. The taper also affects the main jet size your carburetor requires.

(CLIP POSITION) LENGTH: The needle length is determined by the clip position (grooves at top of needle) setting on the upper portion of the needle. On most needles there are 5 clip positions. The top clip position is referred to as #1 and is the Leanest setting. The clips are referred to in numerical order with the bottom position being #5, the Richest. The clip/length setting covers the largest percentage of jetting in your carburetor. With an emphasis at ½ throttle, the clip setting will bleed both up and down to some degree to cover a wide portion of the midrange jetting.

Ideally you like to run the needle setting in either the 3rd or 4th clip position, if possible. The needle clip jetting is especially critical to your machines reliability because on average more time is spent in the mid-range than any other part of the throttle.


http://i94.photobucket.com/albums/l97/zrpilot/needle1.gif

Whew!

[BikeSwimLaugh]

And all this is adjusted in the transmission, right? ;)

Actually, that all makes perfect sense. It's all about regulating the fuel in proper proportion and in accordance with the engines needs to optimal performance and a consistent air/fuel mixture across the rpm band.

Okay, so how do we take into account the bi-polar matrix alignment of the dilithium crystals when the cross-grid field array is misaligned with the subdivision generator exponantor?? The sub-space field accelator would clearly have to be aligned with the grid to radiate a cohesive bond with the anti-matter flux capacitor. Ahhhh....I get it now!

[BEAVER.989]

So ZR, when an exhaust manufacturer recommends a larger pilot and main, but stock needle in the stock position, do you believe this is a bad recommendation?

Do they do this simply because they don't have enough confidence in the lamen to handle the task, or could it be as I mentioned(and read somewhere), that the adjustments to the pilot and main effect the needle, as well?

[Pabst_Powered]

i think my quad needs this done so im really looking in to it, i have a t-4 slip- on and a k&n, pro circuit calls for a 158 main and 58 pilot for this pipe on a ex, i pulled the main out and its still the stock 148(pipe and filter were on when i bought it), my plug reads good but i do have a very slight backfire at high rpm's when i let off the thottle...any suggestions, thanx

[zrpilot]

Originally posted by BEAVER.989
So ZR, when an exhaust manufacturer recommends a larger pilot and main, but stock needle in the stock position, do you believe this is a bad recommendation?

Do they do this simply because they don't have enough confidence in the lamen to handle the task, or could it be as I mentioned(and read somewhere), that the adjustments to the pilot and main effect the needle, as well?

I don't know why they do that... I suppose it might be as you say, in that the average rider can't or won't adjust the needle.

The pilot and the main jet do affect the needle circuit, but only to a VERY small degree.

[BikeSwimLaugh]

Originally posted by Pabst_Powered
i think my quad needs this done so im really looking in to it, i have a t-4 slip- on and a k&n, pro circuit calls for a 158 main and 58 pilot for this pipe on a ex, i pulled the main out and its still the stock 148(pipe and filter were on when i bought it), my plug reads good but i do have a very slight backfire at high rpm's when i let off the thottle...any suggestions, thanx

Hmmm....I'm running an HMF slip-on and K&N as well, they called for a 152 and once the lid on the air-box is removed it seems to run just fine with no back-firing (as you made mention of).

LOL...I had previously thought I was stumbling at the top-end, but turns-out I'm just bouncing off the rev-limiter and have been used to high-revving 2-strokes. These engines do their thing at low/mid range anyways.

I'd try going down to a 154, 158 seems a bit steep...perhaps that's the issue. Please let us know what finally works the best: the slip-in exhaust and air-filter are seemingly the most classic mod's done, so a nice combination of jetting alteration would be much appreciated by all.

[Pabst_Powered]

Originally posted by BikeSwimLaugh
Hmmm....I'm running an HMF slip-on and K&N as well, they called for a 152 and once the lid on the air-box is removed it seems to run just fine with no back-firing (as you made mention of).

LOL...I had previously thought I was stumbling at the top-end, but turns-out I'm just bouncing off the rev-limiter and have been used to high-revving 2-strokes. These engines do their thing at low/mid range anyways.

I'd try going down to a 154, 158 seems a bit steep...perhaps that's the issue. Please let us know what finally works the best: the slip-in exhaust and air-filter are seemingly the most classic mod's done, so a nice combination of jetting alteration would be much appreciated by all. main jet is still the stock 148, didnt put the 158 in yet, i ordered a kit from jets r us and have to see how i do

[bullett]

I only have a slip on exhaust. I've read these quads come a little lean from the dealer and I figured I better jet my quad. I put in a 42 Pilot and a 150 Main jet. Does this sound about right to you guys?

[riderssb250x]

alright guys i have a 450r carb and need help
my mods are

440 kit
hot cam stage 2
no iar box
k&n filter
Lrd pro4 full exhaust
ported and polished head


whats probably a good main pilot and needle clip position

[zrpilot]

Originally posted by riderssb250x
alright guys i have a 450r carb and need help
my mods are

440 kit
hot cam stage 2
no iar box
k&n filter
Lrd pro4 full exhaust
ported and polished head


whats probably a good main pilot and needle clip position

First fix your hot start issue.

[riderssb250x]

need a base line for jeting on a 400 im working on..
im in ri, temp is around 50-75 average,

bike has..
fmf powercore 4 exhaust
removed air lid,
stage 2 hotcam

just installed the cam and removed the lid need some jeting help its at stock now with the needle 4th clip down,

just lookin for opinions

[zrpilot]

Originally posted by riderssb250x
need a base line for jeting on a 400 im working on..
im in ri, temp is around 50-75 average,

bike has..
fmf powercore 4 exhaust
removed air lid,
stage 2 hotcam

just installed the cam and removed the lid need some jeting help its at stock now with the needle 4th clip down,

just lookin for opinions What carb? 450R or stock?

[muad]

N/M, honda400ex2003 already helped me in another thread I started that I had forgot about, DOH!!

[RIDEREDson]

Does adjusting the needle holder and the locknut affect anything?

[flyboy1294]

Hey guys I think I might have a problem.

Disassembled my stock carb last night, checked my jet sizes (Note: I DID remove the jets...) and reinstalled everything today. But it won't start. It cranks and cranks and occasionally seems to almost fire, but then keeps turning. I am sure it has been primed.

I have no idea what I could've done wrong. I'm away from home at the moment, but I will tear it down on the weekend. But in the mean time, does anyone have any ideas of what I did wrong?

If not does anyone have a link to a good Carb schematic?

[zrpilot]

Originally posted by flyboy1294
Hey guys I think I might have a problem.

Disassembled my stock carb last night, checked my jet sizes (Note: I DID remove the jets...) and reinstalled everything today. But it won't start. It cranks and cranks and occasionally seems to almost fire, but then keeps turning. I am sure it has been primed.

I have no idea what I could've done wrong. I'm away from home at the moment, but I will tear it down on the weekend. But in the mean time, does anyone have any ideas of what I did wrong?

If not does anyone have a link to a good Carb schematic?

First loosen the float bowl drain screw to see if gas is in the the float bowl. IF so, it will run out the drain tube all over the ground. That is the first place to start.

Report back.

[flyboy1294]

Originally posted by zrpilot
First loosen the float bowl drain screw to see if gas is in the the float bowl. IF so, it will run out the drain tube all over the ground. That is the first place to start.

Report back.

Alright Will do.

[alberto]

I think my sons 01 might be running rich? Let me know what you think:

full YOSH, K&N, no lid, 170 main (dyno jet kit), dyno jet needle 3rd clip, 3 1/2 turns F/A, stock pilot.

it idles good, nice mid pulls hard, top end is somewhat sluggish. Pops on deceleration. Plug has some brownish dots and black dusting.

I think the bike runs fine but the kid thinks other wise. At this point its all about dialing it in right?

Let me know what you guys think. Your input is always valued. :)

[RIDEREDson]

Mine runs good and fires right up, but I feel like its bogging a little. Would that mean its rich or lean?

[zrpilot]

Originally posted by alberto
I think my sons 01 might be running rich? Let me know what you think:

full YOSH, K&N, no lid, 170 main (dyno jet kit), dyno jet needle 3rd clip, 3 1/2 turns F/A, stock pilot.

it idles good, nice mid pulls hard, top end is somewhat sluggish. Pops on deceleration. Plug has some brownish dots and black dusting.

I think the bike runs fine but the kid thinks other wise. At this point its all about dialing it in right?

Let me know what you guys think. Your input is always valued. :)

Sorry, I don't have practical expereince with Dynojet kits. Try this, drop the main down one jet at a time and see if the sluggishness goes away. Bump up to a big pilot and re-adjust the fuel screw.

[zrpilot]

Originally posted by RIDEREDson
Mine runs good and fires right up, but I feel like its bogging a little. Would that mean its rich or lean?

Depends...:(

[rob_990]

sounds like its rich

[alberto]

ZR,

Thank you for the suggestion. I was thinking of doing that samething. Just needed confirmation from the PRO. I will probably try that this weekend. I will let you know how it goes.

[flyboy1294]

Originally posted by zrpilot
First loosen the float bowl drain screw to see if gas is in the the float bowl. IF so, it will run out the drain tube all over the ground. That is the first place to start.

Report back.

Ok I am home and looked at the quad again.

I am having issues with the float. I'm not sure how the assembly goes. I need a diagram or something I'm using an awful one. When I blow into the fuel line no air gets through at all. I have traced it to the plunger thing and the float.

EDIT:
I got it. Simple installation error:rolleyes:

[RIDEREDson]

So how are you guys adjusting the fuel screw with it idling?

[zrpilot]

Originally posted by RIDEREDson
So how are you guys adjusting the fuel screw with it idling?
I use a Motion Pro 90 degree tool. Some would say it is expensive, but it is some of the best dollars I have spent on motorsports.

[exracer416]

heres my deal i just rebuilt my quad to a 416 11:1 stage 1 cam filter and full yo**** exhaust. i had the 450 cab on the stock bore and i think i need to up the pilot jet now correct? it idles rough and it kinda hiccups back through the carb. also what does the air screw look like on the 450 carb? is it the black cable coming out to the stator side of the machine? also the head pipe got a little red while i was playing with that screw on the black cable if you know what im talking about i put a 175 main in it what should i be looking at for a pilot??

[Ryan'07400ex]

Originally posted by Ryan'07400ex
I'd like to find that thread... do you have the url still?
Thanks

And does a 152 main and 42 pilot sounds good with a hmf slip on, ground down header welds, uni filter, +6 key? I don't know whether to leave air lid on or off with this eihter
Thanks

[Ryan'07400ex]

I just jetted my ex changing it from stock to a 152 main and a 42 pilot. I thought I read that the pilot jet needed to be turned out some instead of tightened all the way. It sort of stumbles when I hit the throttle in the lower than 1/4 range so im thinking I should fo tightened it all the way.
Does that sound like it would cause that? a loose pilot jet...

[wolf400]

can jetting make your bike skmoke?

[Yurshia]

My brother has a 2007 400ex with full hmf sport exhaust, 6degree timing key, stage 2 hotcam, 13tooth front sproket and 39tooth rear, currently running 93octain untill we can find better, k&N air filter and EHS racing power lid.
we ride at about 1100ft elevation. If any1 could put me in the ball park of what jet sizes to start at i would be very great full.

[honda400ex2003]

164 would be my guess to start. it may be a bit rich with that but you shouldnt be too bad. steve

[Chipotle]

03 400ex, stock Carb stock jets, Yoshimura, AMSOIL Ea Universal Dry flow filter with Amsoil pre-filter, ehs racing lid.
14t front sprockt.
I run all 93 fuel.
I know its probably running way too lean.
My header is dark blue within 4min of warm up.
I ordered a 42 pilot and a 152 main.
I plan on removing the choke.
Currently I am getting popping in the Carb and backfiring.
I live in FL so my elevation is 1-30' at the most.
Any advice would be great.

[Yurshia]

Originally posted by honda400ex2003
164 would be my guess to start. it may be a bit rich with that but you shouldnt be too bad. steve
Thanks

[Chipotle]

bump... i could really use the advise

[honda400ex2003]

i would say that around a 158 would be a good starting point with no lid. needle on the 3rd clip position to start off, put the 42 pilot in and go abour 2.5 turns out on the f/a screw. you may be a bit rich with that but it is hard to say. steve

[Chipotle]

Thanks!
I ordered a 152 that will be in Wednesday.
If I use it what settings should I try with it?
I will order a 158 but wont be here in time for this weekends ride so I got to work with what I have.

Also where is this screw that I adjust?

[honda400ex2003]

it may be ok with the 152 i am not sure, i doubt it will be good though, sounds too lean with the lid off. If you are lean you can put your lid on for the weekend to make up for the lean condition until you get a bigger set of jets. I would suggest getting a few jets since it could be different from what i recommend. there are many factors to consider that i cannot do when suggesting something. Elevation, temps, flow, lots of things to consider, i try to always go to the rich side of any recommendation so that it is not at risk of blowing up. The f/a screw is on the bottom of the carb in front of the bowl. I would definitely do some researching and such to learn about jetting before doing it. it is not as easy as just changing jets it is really a science and can take lots of time to figure out if not done right. you will probably want to do some plug chops, do a search for this and see how to do it, along the way read the threads along with the plug chops and it will get you a better understanding of the whole thing. There are certain parts that are important during different times in the throttle position, such as a pilot being from idle to 1/8 throttle, needle from 1/8 to around 1/2-3/4 and main from 3/5 to full throttle. this is an estimate since i did not look to figure out what it is exactly. steve

[Chipotle]

Thanks Steve!
I have rebuilt Boat carbs in the past but these are a bit different.

I will run lid on this weekend. As of right now I think I am over heating within just a few min of riding.
Within 4 minutes of idling my exhaust is a dark blue.
I am scared its way to hot.
I cant keep it idling with stock jets and lid on without giving it 1/8 - 1/4 throttle.
I have been smelling a weird smell wile running recently. (dont know how to describe it.)

[honda400ex2003]

i would say you should be really close if not a bit rich with the lid on with your slip on and the filter. I ran a 150 with my t-4 and k&n at 1500ft. if you are at sea level a 152 will be just about perfect for you. I would suggest leaving the stock pilot in and going 3 turns out on the f/a for the weekend. this way you will not be changing too much and making it run worse than it already is. just my .02 though. lol. steve

[Viktor_trx400]

My buddy has jetting problems a high rpm. Her bike is 06 all stock with k&n filter, lid on and pro circuit full exhaust. Now is running 150 dynojet(165 keihin) for main jet, stock needle and 3 turns f/a (1500ft). thanks in advance

[honda400ex2003]

what are the problems she is having. may be a bit rich imo i would go with a 160 and it would probably be just about perfect. It is most likely doggy with it being rich, try a 162 first and see how the plug looks after a couple of good wot runs. steve

[Viktor_trx400]

sorry is a friend wich has jetting problem. He only tell me that has jetting problem a high rpm. Tomorrow ask him what problem has. thanks

[Viktor_trx400]

Originally posted by honda400ex2003
what are the problems she is having. may be a bit rich imo i would go with a 160 and it would probably be just about perfect. It is most likely doggy with it being rich, try a 162 first and see how the plug looks after a couple of good wot runs. steve

The jetting problems solved, thanks

[Yurshia]

My brother has a 07 400ex with stage 2 hot cam, ehs power lid, k&n air filter, 6degree sparks timing key, full hmf sport exhaust and rest of bike is stock.
He bought a jet kit and the jets r us jet kit recommended using the largest jet and working your way down. Which is a 180. With the 180 in the carb the quad seems to run good all but on a hard pull in second gear. it seems to bog when on it hard in 2nd. Does this mean he should step down in main jet size? or buy some larger jets and keep trying?
any help would be deeply appreciated.
thanks

[a4guy]

I have a 03 400ex with a FMF Tunable T4 slip on and a K&N cone filter with no lid. Ordering a FMF Power Up Jet Kit and need to know what jets to start with. I am at 797 FT and my temp is usually 50-80 degrees fahrenheit. Any help would be great.

[Built_300EX]

Exhaust glows bright red, can be seen VERY easy in the dark only after minutes of idle.

Gas is getting into my engine oil.

From what i've seen I know this.

185 main, 38 pilot. Port/polished (atleast from what I see, and feel.) t4 full exhaust system, moded air box lid, k&n filter cover, K&n filter,

Also, the quad doesnt lug, its fast, responsive as can be. Whats causing this? Tons of compression, starts right up, after about 1 second of holding start if that. Basically as soon as I touch it.

What other mods could this have to run good with that jetting? Also, how if it is running lean from the pipes glowing, is there gas getting into my oil?