engine dies when braking

[bigbore2]

 84 1100---    I like to coast to stoplights, stop signs in neutral at times. So say I am going 25 mph or 35 mph, pop in neutral and coast the rest of the way in neutral at idle.  Don't ask why, I don't know why I do this.  Anyway, the engine dies when doing this. I can be only going 5 mph and it will do this also with quick braking.
Full throttle acceleration seems normal.

I was thinking that the float level, if too low, may cause this. I set float level to stock specs when I redid the carbs a couple years ago.
What do you think?

[Pat Conlon]

What is your warm idle speed?

[Zwartie]

Bigbore2,

I don't mean to hijack this thread and I'm sure you going to get lots of great advice from FJers who have likely forgotten more about carbs than I'll ever know. Regarding the "coasting to a stop in neutral" I would suggest that you stop that practice immediately. A motorcycle coasting in neutral is a motorcycle not in control. I'm not saying you need to downshift and release the clutch in every gear as you slow down but at the least you should always be ready to accelerate at a moment's notice because you never know what the situation may demand. Coasting in neutral is never going to get you out of trouble in a hurry. Sorry, it's my inner motorcycle instructor talking!

I'm sure you'll get the stalling / carb issue dealt with.

All the best,

Zwartie

84 1100---    I like to coast to stoplights, stop signs in neutral at times. So say I am going 25 mph or 35 mph, pop in neutral and coast the rest of the way in neutral at idle.  Don't ask why, I don't know why I do this. 

[bigbore2]

idle speed is 1400-1500.  Idle is not good and i have been trying to sort it out, but not yet accomplished. I think it is a little too lean yet as it pops, sputters, etc.  same symptoms up to about 2000 rpm [where the needle starts taking over] with the pop, etc.   It is dangerous to take off trying to shoot the gap between traffic unless I am up over 2000 rpm.  Bike will hesitate, pop.

I just thought I better have the float level correct first to get the pilot jet sorted out.  funny thing is my dirt bike had the same problem until I went way richer [up 3] on the pilot. {float level set to stock height} Now dirt bike idles perfect and starts 2 kicks cold and one kick hot.   We are at 5000 ft. [KTM380 2stroke] I have not tried the coast in neutral and then brake with it.

1100 engine has needed more fuel everywhere also. I think I had to go up 3 on the main to 122.5 to get that main close. Less rich than that, it would lean surge at WOT. [4 into one Yosh and Uni pods] I have gone up 1 or 2 with the pilot already. Air/fuel screws out 3.5 or 4 turns, so nothing left there to adjust.
I was just thinking if the fuel sloshes forward in the bowl with braking,  that might kill the engine, if level was too low.

Can I safely raise the float bowl level in 1mm increments to see if that stops my symptom?  or should I work with the stock float level?

[Pat Conlon]

My opinion below assumes your carbs are clean esp. the idle circuit, float needle seats and you have no vacuum leaks. Be sure about this first.
Also, check your choke linkage. Make sure your carb choke plungers are fully extended in the off position and the choke rod linkage is not pressing on the plungers. Even the slightest pressure pressing against the choke plungers, coupled with the vibrations from the engine, will cause fuel to seep into the choke circuit causing a rich condition. I learned this on my '84 the hard way.

You're at 5,000'. Your bike studders, hesitates and pops at low speed.
You are too fat (rich) You're masking it by setting your idle too high.
Before you play with your float levels, check your fuel level in the bowls. You may need to lower your floats, not raise them. High float settings will cause a over rich condition.

Assuming you have stock 155 air jets, going up 2 sizes on your pilots (from 37.5 to 42.5) and air/fuel screws out 3.5-4 turns, at your altitude sounds awfully rich to me.

With the bike fully warm, do the blip test. When you close the throttle if the idle drops below the set idle speed, (idle dip) then returns up to the idle speed, means you are too rich. What can be happening is when you are coasting with your throttle closed, the rich setting is causing the idle to dip to a point where the engine stalls. Turn your fuel/air screws in (leaner) using 1/4 turn increments to see if the condition improves.

Another point where the engine can be getting too much fuel is from leaky float needle seat O ring(s) If it's bad enough, you would notice this by fuel pissing out your carb choke vents or bowl vent lines. If you haven't already, replace those float needle seat O rings with a fresh set.

Again, all this ^^^ assumes your carbs are clean, if not....all bets are off.

Zwartie is absolutely correct in his advice...listen to him. It might save your life.

[bigbore2]

Carbs cleaned and rebuilt 3 years ago. I am still learning tuning, but know when it is right.  

If you are right Pat, then I can just go back one or two on the the pilot and retune.  I do have carb synch tool also, which I did use on this bike. I will try that and get back to you.

I thought going up to a 122.5 main seemed awfully rich, esp at my altitude, but that is what this engine needed. I hope you are right  and i just did not get it tuned before correctly as I was going up in pilot jet size.

[Flynt]

bigbore - sounds like you're aware of this tuning sequence for CVs, but just in case:

http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,cv,high_rpm_engines.html

You can get axle wrapped pretty quickly if you jump around in the sequence.  I've found you want to go as lean as you can on step 1, but if you raise the needles too much to get the upper midrange correct you will be better off to go up one size on mains...  you won't have max power at high RPM WOT, but lower midrange will behave much better.  YMMV.

Frank

PS - all credit goes to Marc S...

[bigbore2]

Yea, that is a good guide.   It can't hurt to re-estabolish the sequence from the top down. My suspicion is to increase my pilot to get what i want. I did raise the needles but took it off. I will put that back also.  Carbs have to come out to do anything anyway.  Glad I junked that damn airbox.