Jetted Right??

[TouchUps]

How do you know when your bike is jetted right? I got a 2000 400ex big bore 440, pipe, cam, ported, etc. Just bought it used last week. It runs fine, but wondered if it was jetted right to get the most out of it. I have always had 2 strokes. You can read the plugs on those to tell if it is jetted right pretty easily. It came with a Clymers manual, but it is kind of vague on the jetting stuff. Thanks.

TouchUps

[James Parent]

theres a post or two somewhere about this jetting stuff.. if your referring to your main jet.. you have to do a wide open throttle test.. search here, there is a lot of useful info

[cals400ex]

let us know what jets are in it. are they keihin or dynojets?? i assume it has the stock carb on?? tell us the sizes in it too.

[TouchUps]

Here is what dude told me it has:

440 big bore
cam (dont know specs)
HMF pipe
larger valves
open air box with K&N
stock Keihn carb

Thanks for the responses so far. I will tear into it and find what jets it has now. What concerned me the most was that it pulls hard in 1st and 2nd, but 3,4,5 are just quick "shift jerks", but no real pull after that. I have had a Blaster, Banshee, and now I have a '03 CR125 and this '00 400EX. New to thumpers, so not sure what to expect. I like it though. Jumps smooth and handles good.

Thanks Again,

TouchUps

[zephead400ex]

Sounds like you need to go up on the main jet, but until you find what what you are running with it is hard to tell.

Get back with us man, we'll do what we can:)

btw, welcome to the site.

[TouchUps]

OK...this is what I got:

Needle Jet has no markings on it.

Main Jet is 160

Jet Needle is B44A or B44(delta symbol)

Slow Jet is 45

Pilot Jet has no markings and was 1 1/2 turns out

Thanks.

[cals400ex]

that jetting may actually not be all that bad. where was the clip located on the needle?? by the way, that is the factory needle (B44A).

also, i assume you mean the fuel skrew was about 1.5 turns out, not the pilot jet??

[TouchUps]

Clip in #3 position (center). Yeah, it is definately the pilot jet I am talking about. According to the Clymers manual, the pilot jet should be 2 1/4 turns out. How critical is the pilot jet setting?

Thanks Again,

TouchUps

[cals400ex]

what your referring to as the pilot jet is what most people refer to as the fuel skrew. this skrew is a fine tune adjustment for the slow jet (what most people call the pilot jet). so, 2.25 turns out is a good place for a stock bike. after that, you just need to tinker with it a bit. this jetting mainly controls fuel at idle to 1/8 thorttle or so.

[TouchUps]

So what do you guys think? Does that jetting sound alright? How do you know AND can you hurt a 4stroke running it to lean? Where would you recommend the needle clip be set at? Thanks for any help/advice.

Touch-Ups

[cals400ex]

there are a lot of factors that matter when jetting including air temp, elevation, humidity, modifications, etc.

it will be hard to tell. also, some people prefer to run their bikes a little leaner than others. if it is a little lean, it will definately be harder on the bike and will need a more frequent rebuild. i would try a 40 or42 pilot jet and the 4th clip on the needle. your mainjet seems fairly close. just some trial and error is needed when it comes to jetting.

[James Parent]

I'm near sea level too in NJ, the temp is like 60+
I just ordered a 165dyno jet, and right now my fuel screw it 2 turns out, third clip on the needle.. outerwears airbox lid..
this sound about right? k&n filter

[cals400ex]

Originally posted by James Parent
I'm near sea level too in NJ, the temp is like 60+
I just ordered a 165dyno jet, and right now my fuel screw it 2 turns out, third clip on the needle.. outerwears airbox lid..
this sound about right? k&n filter


sorry, i don't use dynojets. i use keihin jets. the numbering pattern is different. i would try to pm "ewalker" or "rico" and see if they can suggest anything. i have a feeling they will both suggest a smaller jet. by the way, the dynojet kit comes with a different needle.

[hondarider2006]

Originally posted by cals400ex
by the way, the dynojet kit comes with a different needle.

And that needle is a pain in the @$$. I have it in right now, and haven't been able to get it 100% dialed in sense I got the kit...6 months ago. The stock needle is going back in this summer;)

[KY Woods Rider]

The only way to know what jetting you need is to test it, but I'll give you the general neighborhood where I think it should be, which of course may or may not be where it truly needs to be since I can't ride the quad and check it out for myself. Also, you didn't mention the altitude and temp, but I'm just going to assume you aren't at a high elevation and the temps aren't excessively hot or cold. So, here's what I'm thinking based on the info so far...

Main jet: It would be nice to know whether or not the one that's in there is a Dyno or Keihin jet. I have no clue about the numbering system of the Dynos, so if that's what it is, you'll have to get info from somebody else about how well it will work. If it is a Keihin jet though, I'd say it's a bit too lean for all the mods (440, large valves, open airbox, etc), I'm thinking it should be somewhere around a 165 or maybe even a 170.

Needle: The clip needs to be lowered one notch so that it's in the 4th groove from the top.

Pilot and screw: It's probably okay with the 45 and 1.5 turns out, but you could try a 42 pilot at 2.5 turns out.


Reading the plug on a 4-stroke is basically the same as a 2-stroke, although there is a slight difference. A 4-stroke plug can be read just like a 2-stroke, it will just read a bit lighter. A 4-stroke is jetted about perfect when the plug is a tan to light brown color. And yes, running a 4-stroke too lean can cause damage, although to really damage a 4-stroke, you either have to be running it waaayyy too lean or running it just a little too lean for a long period of time.

As for how to check the jetting for yourself, below is a partial copy and paste of a post that I wrote on another forum to help a guy figure his jetting problems...

I assume you know how to do a plug check for the main jet, but here's a quick overview. Run it WFO, kill it at the same time you let off the throttle, do a plug check. This will tell you where you need to go with the main jet.

The needle is probably the hardest thing to get correct and it is very important because it controls the throttle settings you ride at most often (approximately 1/4-3/4). I do two things to check my needle position. First, I do a run similar to what I do to check the main, only instead of running WFO, I run it at a steady 1/2 throttle. Just run it at approximately 1/2 throttle (be sure to never let it bog while doing this, a higher RPM doesn't matter), let off and kill it at the same time, and then do a plug check. After I've done this, I also do a seat-of-the-pants test to verify it. If it's too rich, it will feel sluggish, the throttle response between 1/4 and 3/4 throttle will be poor, and it may also have a slight hiccup right above 1/4 throttle just like you've flooded it for a second (which you did if this happens). If it's too lean, the RPM will jump up quickly and you'll get a very sudden burst of speed as you come onto the needle (a little too lean) or it will have a surging feeling like it doesn't know whether to pull hard or not at all (way too lean). If it has a smooth but crisp pull between 1/4 and 3/4 throttle, then you're fine.

The slow circuit (pilot and screw) effects everything from idle to approximately 1/4 throttle, as well as decelleration (because the throttle position is back to idle on decel). You can tell a lot about the slow cicuit just by how the quad starts and the results of idling. If you can start it in cold weather without the choke, then it's too rich. If it's hard to keep running after you start it (of course it does need a bit of warm-up) and wants to keep dying until the motor has had several minutes to warm up, then it's too lean. Another way I check it is to ride it around and get it warmed up to normal operating temp, then let it sit and idle for 5 minutes. During that time, if the headpipes start glowing and the motor is extremely hot, then I shut it off and put in a bigger pilot jet. If it does okay, then I shut it off and check the plug. If the plug is white (just like a new one), then you're too lean and you'll at least have to adjust the screw and maybe go to a bigger pilot. It's normal for it to be a bit darker from all the idling, but if its black and crusty or black and wet, then you're too rich. You can tell a lot from the decelleration too, but many people get confused on this due to the slightly different sounds that can come from the exhaust, so you have to really pay attention to the sound. If you hear a loud and sharp "crack", then you're too lean. If you here a deep toned "poof", then you're too rich. If you're too rich, your buddies may report that they see white smoke come out your exhaust when decellerating after a hard WFO run, but that white stuff is raw fuel. However, if you're running an open and very high flowing aftermarket exhaust, it's pretty common to have that "poof" sound on decel from to time, even if the quad is jetted perfectly.

[James Parent]

the dynojet kit comes with a different needle.

Yeah sorry.. i had the dyno jet in my bike, and lost the rest of the jets :( i moved.. but i just took my airbox lid off and ordered a 165.. the kit called for a 170 with 3.5 screws out on the screw, and third clip on their needle..

if anybody else has imput.. does a 165dj with 2.0 screws out with a dynojet needle on the third clip sound right?

[TouchUps]

Now I have other problems....

Went ridin today....muddy and wet but not excessive splashing or anything. Anyway it did fine then all of sudden starting having problems. It will idle for awhile and then just about blow the carb off and die. One time I left the air filter side boot off the carb and let it idle just to see what was happening and it literally blew the carb of the engine side boot. When you give it a little throttle it sputters and runs terrible. If you hold it open anywhere (1/8, 1/4, 1/2, etc.) it tries to die and then will "hit" for a second than try to die over and over. Any suggestions??? Thanks.

[cals400ex]

Originally posted by TouchUps
Now I have other problems....

Went ridin today....muddy and wet but not excessive splashing or anything. Anyway it did fine then all of sudden starting having problems. It will idle for awhile and then just about blow the carb off and die. One time I left the air filter side boot off the carb and let it idle just to see what was happening and it literally blew the carb of the engine side boot. When you give it a little throttle it sputters and runs terrible. If you hold it open anywhere (1/8, 1/4, 1/2, etc.) it tries to die and then will "hit" for a second than try to die over and over. Any suggestions??? Thanks.


clean the carb and make sure no jets fell out