Basic Carb Info

[PitterB4]

Some Basic Carb Info
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Minbo
(11/14/00 11:20 am)
Carb problems

Are the float height measurements in the shop manual? I cleaned my carbs and now it's very rich (stumbles and kills w/o a lot of idle screw) under 6000 rpm. I think I put the floats back in the wrong bowls or something. The top end feels better, but that may be due to the low and mid being so bad. I may order a Factory carb recal. kit if it's under $150. Any other carb advice is welcome. I noticed the main jets are 105. Is that stock?
 
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Hammer117
(11/14/00 6:47 pm)
Re: Carb problems

The stock mains on my '91 are 102.5's.
The floats control the rpm up to about 3k.
The needles control it to about 7.5k. Then the mains control it from about 8k to redline.
Go to www.factorypro.com and take the cv carb link at the bottom. There is some excellent info on carb tuning in there.

Shane CCS#217 WERA#417

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Minbo
(11/15/00 10:45 am)
carb problems

Thanks. I'm gonna gonna check the floats and needles. The factory pro recal. kit is $100, but I'll put off getting it unless I have to. A shop I trust wants $500 or so for a complete carb service. So, now's my chance to learn.

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Hammer117
(2/1/01 8:35 pm)
Factory Pro's Website

Go to www.factorypro.com and click on the cv carb link at the very bottom. It is a must for jetting carbs.
CV carbs do have slides and the B4 diaphram (mine anyway) does not have a notch. The slide/diaphram is made together and the slide will only fit into the carb body in one orientation. Another tip...plug one of the two holes on the bottom of the slide with just enough epoxy. This will improve acceleration a good bit. Don't use too much epoxy because you want to keep the weight to a minimum. Works like a champ for me.

Shane

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Minbo
(2/7/01 3:23 pm)
carb tuning

Thanks for the info. I screwed with 'em as much as I could and I still didn't get things right. Below 6k I'm certain all four weren't firing form the sound and pipe heat. Then above that all hell breaks loose. I finally sent it off to the shop last night. The carb clean/snyc is about $225 plus parts. It's been off the road for 2 long months.
 
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Minbo
(2/14/01 10:24 am)
carb problems no more

Well, it's fixed. They just needed a thorough cleaning and adjustment. It's a bit more perky and way better throttle response.

[PitterB4]

DjSuperfly
Registered User
Posts: 4
(9/26/00 3:10 am)
 Question regarding carbs...
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 I know my motor is running way rich...heavy black smoke on start up, and a few minutes after start up...on hard revs also...

I also have a real hard time starting it when it's coller outside...if I can't get the motor to sart up on the first try...it's hopeless...I have to do a push start and once it's started, really crank the motor to burn the excess out in order just to get the motor to stay running...but once she warms up a bit, no stalling problems, just that heavy black smoke on hard revs...

Now, I'm pretty new at this whole motorcycle business...but heavy black smoke indicates richness...?...second, I do know that my bike does have a stage one jet kit...question is, could the kit be causing this problem (in the sense that it's bad parts in the kit, bad workmanship when installing it...???...another mech quoted me about 3 hrs to look and recalibrate my carbs...does this sound correct to you guys...?

Thanks guys

Bao Nguyen
91 b400 Red
Madison, WI
 
The one armed Bandit
Registered User
Posts: 8
(9/26/00 3:59 pm)
 Re: Question regarding carbs...
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 High tuned 400s are very sensitive to air/fuel mixes. Yes you are running rich. (have you made sure your choke cable is not kinked?) If you smoke when you rev you might have to alter the needle position. That is, if your rings are not bad and the problem is confined to the carbs. But before you start look under the headers at where they come out from the engine. You will see some bolts. That is where you attach an exaust gas analizer! I have never seen this on any bike before! It's trick! It's to get the air/fuel mix perfect and attain the most power. You would only need this on a race bike or an engine in a relativly high state of tune. You might want to leave this to someone with an analizer. However, if you want to lean the mixture out there are adj. screws on the bottom/front of the float bowls. First screw these in until they seat gently. Then back them out 1 1/2 turns. This will probably be too rich so watch for black smoke. When the engine is warmed up back them out 1/4 of a turn at a time until the smoke goes away and the engine does revs freely. That's a half-assed way to do it. By the way I forgot to ask is there an after market exaust on the bike? Also, you could call up the company that made the jet kit and ask them what the baseline settings are. Lastly, it could also be other things, not necessarily the air/fuel. Good luck.