Why am I rich?

[MtnEX]

OK, so I take the carb apart...

I'm hurting the guy who did the jetting if I ever see him again... for over-tightening my screws...

Anyways, I have a 38 pilot and a 155 main, needle clip in the third.

I have a K&N and a full Yoshi exhaust.

According to 3 sources, that should be right on... but my plug reads rich.


If I can find something to work for the valve arm set screw, I'm going to try moving the clip on the needle, setting the pilot screw at 2 1/4 - 2 /1/2 turns out... and trying to figure out how to syncronize the throttle assembly...

What could I try on the needle?
Taking off the airbox lid was not enough to lean it out...

well does it feel like its running rich? when its rich it will bog and cut out of you stab the gas. if its lean it will run like crap and cut out with out instantly if you stab the throttle. how are you doing your plug checks?

[justin1022]

id mess around wit the fuel/air mixture screw.

[MtnEX]

Originally posted by FoxHondaRider
well does it feel like its running rich? when its rich it will bog and cut out of you stab the gas. if its lean it will run like crap and cut out with out instantly if you stab the throttle. how are you doing your plug checks?

Well, it's not really bad.

I find the throttle response to be mushy... but I own a 2 stroke also, so it's hard for me to judge. It does not seem to pull like it ought to, but there again I have the same judgement issue.

I can tell you if you hit the throttle quick in neutral there is a studder right off the bottom. Also, if you hold it in the needle in neutral, you'll get some sputter and some rich smoke.

Plug readings I am doing in all 3 ranges... well I take that back, I haven't done two good ones at wide open throttle.

[MtnEX]

Originally posted by justin1022
id mess around wit the fuel/air mixture screw.

Yeah, I did that... and I found it was way far out from seated. Exactly how far... well I really should have counted.

I set it at 2 1/2 turns out...

Any suggestions on where or how to tune this circuit?

testing in neutral is not a fair way to get any readings...the motor needs a load on it it

a 4 stroke will not pull like a 2 stroke..i will say the 450 class bikes are a lot closer than the 400ex, but still not the same...so you can't use that as a comparison

the screws that he over tightened are brass and strip easier than they come out

[MtnEX]

Originally posted by speedyquad
testing in neutral is not a fair way to get any readings...the motor needs a load on it it

a 4 stroke will not pull like a 2 stroke..i will say the 450 class bikes are a lot closer than the 400ex, but still not the same...so you can't use that as a comparison

the screws that he over tightened are brass and strip easier than they come out

I never said I was taking any readings in neutral...

I was just pointing out what it does in neutral in response to throttle... because my seat of the pants opinion is unfair due to the fact I also have a 2 stroke.

[MtnEX]

OK... I have a question... might be a dumb one too...

The needle jet holder itself... the part the main jet screws into...

Well, where it screws into the carb, there are a lot of threads, and also a lock nut...

How do you know you have the holder at the proper depth?
As in screwed into the carb....

taking readings OR what it does in neutral does not help us out...it needs to have a load on it for a true diagnosis...that was my point

what do you mean by the needle jet holder...the arm that actuates the slide. the one that holds the needle in place? if that is what you are talking about, it should be flush with the slide where it screws in...

are you running a dynojet setup? do you mean the adapter for the dynojets? i am not sure what you are talking about

i am going to guess that in your sig, it says k&n filter and jetting, that means a k&n jet kit...that kit is just a rebadged dynojet p.o.s....go to your local dealer and get some stock jets...you'll have a lot less headaches for it...

[MtnEX]

Well, I can't be fair to the quad in saying how it feels I don't think.

It don't spit, spudder, miss and just generally run like crap under load. But to me it does feel a little flat, mushy, boggy, unresponsive. Could be all in what you are used to though.

I know it's rich because I see the soot in the exhaust... and the plug readings are dry carbon black, even without the airbox lid.



As for the internals of the carb... OEM jets I think...

The needle goes down into the needle holder from the top.
The main jet screws in the bottom of the needle holder.

The needle holder also comes out of the carb.
Back off the lock nut and it comes right out.

But there are lots of threads on that thing.

Maybe it only screws in so far... then the locknut secures?
I dunno...

[krt400ex]

Originally posted by MtnEX
Well, I can't be fair to the quad in saying how it feels I don't think.

It don't spit, spudder, miss and just generally run like crap under load. But to me it does feel a little flat, mushy, boggy, unresponsive. Could be all in what you are used to though.

I know it's rich because I see the soot in the exhaust... and the plug readings are dry carbon black, even without the airbox lid.



As for the internals of the carb... OEM jets I think...

The needle goes down into the needle holder from the top.
The main jet screws in the bottom of the needle holder.

The needle holder also comes out of the carb.
Back off the lock nut and it comes right out.

But there are lots of threads on that thing.

Maybe it only screws in so far... then the locknut secures?
I dunno...


as to your Q on the locknut. on the stocker, it is seated right up against the main. no threads in between. when you screw the main in, there should be no visible threads, and when i jetted my quad that is the way i kept it.

[MtnEX]

Originally posted by krt400ex
as to your Q on the locknut. on the stocker, it is seated right up against the main. no threads in between. when you screw the main in, there should be no visible threads, and when i jetted my quad that is the way i kept it.

I didn't know what to do really, so I cleaned and inspected everything. Then I wanted to get it back together so I could try it out during daylight hours tomorrow. But I wasn't getting the feedback I'd hoped for so I just went to it.

I did not put the needle holder back like it was in there. I threaded it in as far as it would go. Then snugged the lock nut down to hold it in place... then screwed the pilot into it. Looks similar, maybe less threads than in the pic in the factory service manual. Right or wrong... I dunno...

I didn't get any feedback on the needle clip either, so I just raised it one notch... from the third to the second. Right or wrong, I dunno.

As for the pilot screw, I set it at 2 1/2 turns out... probably wrong.


All I know at this point is that somehow before I took the carb off, my idle mixture leaned out. All it's done is idle lately. When I pulled the plug, the center electrode was tan white, the rest of the medal black. It had been doing wierd things at idle, so I am not surprised.

I'm going to leave it be as I have it now though and go from there. It fired and ran on the first try, which is better than I expected for the first time I tore the whole carb apart and messed with it.

It did not start as easily though... so I may need to make some adjustment... or there may be something to be said for jumping to a 42 pilot. We shall see.

[GPracer2500]

About the needle jet holder: your assumption is correct. It just screws in all the way until it bottoms out. Then that nut is there to secure it. The needle jet holder is not an adjustment point.

About tuning your pilot circuit: there's a how-to in the "How-To" section describing the technique for jetting that circuit....titled something like "How adjust your fuel screw". I'm too lazy to link to it.

About your main jets: make sure they are genuine Keihin jets or at least follow the Keihin scale (i.e. no jet kit jets). If they are genuine Keihins there will be a stylized "K" stamped next to the number. Any jets should work....but if you're going to talk specific jet sizes you can't unknowingly be using Dynojet jets. There sizes run larger.

About you're needle: So you raised the clip? That lowered the needle so now your a bit leaner around 1/4 to 3/4 throttle. Was it rich before in those throttle positions and if so did the change improve anything?




Aside from all that, your 400EX is never going to have the snap and throttle response of a two stroke. In mostly stock form, they're just not like that. By all means, tune the carb. But don't use your past two-stroke experience as a yardstick for what a correctly tuned 400EX feels like. If you're thinking 250r, Banshee, most any two stroke dirt bike, etc.....a stock carb'd 400EX does respond a bit on the sluggish side. Get an FCR if you want good throttle response.

In the mean time, get a bunch of jets together and start experimenting. Make one change at a time, test it (testing usually only takes minutes of ride time), then make an incremental change to that same thing, then test, and on and on. Just remember the throttle positions correspond to the jetting circuits--very little is rpm dependent.

It helps to get good (fast) at making jetting changes. Swapping mains on an EX takes 2 minutes or less with practice. The faster you can make changes, the easier it is to detect what you just did. If you're not sure you can tell the difference, make bigger steps at first. Don't just ride around aimlessly when you're testing (not saying you do now). Deliberately operate the throttle in the range affected by your change. Concentrate on sensing what the bike does when you operate the throttle in a specific way. Do that same thing after each change to evaluate if performance is increasing or decreasing. If you're really into it, get a friend and a stopwatch and start timing roll-ons.

And write everything down! It really helps! If you write everything down you can always go back to the last time it still ran well. And my opinion is that many/most people have better success NOT using plugs for jetting. It can be tricky business that leaves you chasing your tail. I think orderly experimentation is the best way for many people. ok, i've rambled enough

[MtnEX]

GPracer,

Thanks for the post. I'll have to check that how-to.

I've tought this EX was a bit of a slug from the beginning... so that's not really why I went into the carb.

I noticed the jet job I got wasn't so hot when I saw flood smoke and black soot buildup inside my silencer. So I pulled the plug and found it black also. I knew it was too rich and needed correcting. I was basically getting a black plug pretty quick from all the jetting circuits. I also saw I had black on top of my piston.

Along the way, I also had it to leak fuel out that bottom tube on the carb. So I wanted to see inside the bowl... the float valve, etc...

As for the changes I made, I won't be able to find out how they worked out until daylight.

[MtnEX]

Well, I didn't have time to fool with it much today.
Just rode it for a few minutes... no plug readings...

I rode it just to pay special attention to it's response in all running circuits.

It does not start as well as it did. The idle RPM still changes at different points in the run. Pilot needs work.

Needle response is about the same...

I might not have been getting in the main before. I am now. There is a bog there, and then it goes insane with response.

It's still rich I think.

[MtnEX]

Well crap... it's raining non-stop today. Not that I mind so much, it's just that having this unresolved is going to drive me mad in the meantime. Things like this bother me if I'm not piddling with them until they are done.

It's probably for the best though. I only have 12 hours between shifts and an hour of that is gone already.


Anyone have any thoughts on where I'm at with it now.
I know I need to get those plug readings, but the weather is not cooperating.

[MtnEX]

Well, it finally stopped raining for a few minutes. So I went and pulled the old plug I put in it to drive around yesterday. It was jet black when I put it back and I was just wanting to see if anything changed at all.

Then I put it back and cranked up... because it's a nice 60 degrees here. Anyways, I took a picture of the plug because I was surprised by it. I 'think' I did the right thing on the needle. But I'm a little confused on the pilot... I was idling very high when I shut down, but at cold startup I'm low.


Hold on... the file size on my pic is too large... errr!

[MtnEX]

Let's try this size...