Front cylinder running rich 900cc aircooled(keihin)

[lechef]

My engine is running rich on the front cylinder, it pops and hesitates to run after just 400meters but starts out ok. When i take the plug out it is wet from fuel.

I have good spark on both cylinders and i have set the floater to the right hight (9mm).
I figured it flooded so i changed out the float assemblys between the carbs and nothing changed so it is prabably not flooding but it might be....
Can it be the slow air something or an airjet that is clogged by something causing it to run rich?
It idles great but when you go for a ride it starts having problems.
I have tried to switch the coils aswell but noting changes.
Its either something in the carb or something under the alternator cover pic ups etc.

I have keihin fcr 41 carbs.
Last edited by lechef : Yesterday at 8:50 am.

[lechef]

Nobody that can help me?

[neno]

Yeah I'm not really familiar with the carbed bikes... but i'll just bounce some ideas. If you have good spark and are sure you have good spark after it warms up it is definitely in the carb. If the jet was plugged in any sort of way you would think it would run lean from lack of fuel. Do you have to sync the throttle bodies on carbed bikes (might be a dumb question)? If it were me I would take the carb off and just give it a good cleaning/check and go from there. I know its not much but I hope it helps.

[Old Fart]

With that much fuel it can only be three things. Here's a few basic things to check.

The float needle is allowing fuel to pass. Remove the carb and clean the float needle seat with a cotton swab and carefully wipe the float needle to remove any accumulated deposits.

Check that the slide needle is secured correctly with it's clips. If the needle is located much to high it will pass excessive fuel at 1/8 to 3/4 throttle.

Check the needle jet holder, (the thing the slide needle slides into that allows metering of the fuel.) These can wear on high mileage 900's and also allow too much fuel. I don't know how much time are on the 41 fcr's though.

Lastly as the bike is a bit older there have been ignition pickups that have been known to breakdown that causes misfiring. They will still measure serviceable with a resistance rating but breakdown when warm. There is an aftermarket source for these to avoid Ducati prices.

[lechef]

Hope its not the pic ups, best way to check is to run the bike hot then check for spark i guess?

[Old Fart]

You'll have spark regardless. But bad pickups will trigger a bit erratic often having misfires and generally feeble ignition.

Not knowing how the carbs are adapted, but can you swap them around? If so you should then have a good front cyl and a bad rear. If that's the case you just eliminated the pickups and it's time to dig deeper into the carbs.

[lechef]

I ran the bike yesterday, it runs great when you drive it even under full load its just like normal.
But when you idle and stand still the fron cylinder gets rich causing the engine to die, can it be the air screw that has changed? or the fuel screw.
So it has spark even better then i have seen in a long time since i cleaned everything out.

Its a pair of keihins.

Originally Posted by Old Fart

You'll have spark regardless. But bad pickups will trigger a bit erratic often having misfires and generally feeble ignition.

Not knowing how the carbs are adapted, but can you swap them around? If so you should then have a good front cyl and a bad rear. If that's the case you just eliminated the pickups and it's time to dig deeper into the carbs.

[Old Fart]

Air and fuel screws only affect idle.

Check the slide needle. If it's jacked way up it'll pass enough fuel for a 454 chevy.

[BrianK]

lechef, I run 41mm FCRs on my 97 900SS CR. Got em from Chris Kelley who is generally great but I did find that although supposedly correctly jetted for my bike, they were WAAAAY rich. I had to do a fair amount of experimentation before getting them dialed in. This is with K&N pod filters, 11:1 pistons and a Dyna coil.

I can look up my settings if you'd like them, but as I recall, among other things I reduced the main jets from 155s to 145s (maybe 140s - again, let me know if you want me to look up my settings, I have them recorded) and raised the needle clips several notches. Believe I had to give more slow air and less slow fuel also - EVERY setting was too rich.

They were giving me 35MPG when delivered. Plugs were black. Last tank, I got ~50MPG, and the plugs look great.

Power is and always has been fine. - B

[BrianK]

Okay, checked my settings. I ended up with:

145 mains (were 155 originally).

Needle clips in position number 2 (second from top). I believe they started in position number 4 or 5.

Slow fuel screws out 1.0 turn (were 1/2 turn). (This was final step, to cure some popping on decel.)

Slow air screws 2 turns (were 1-1/2).

Those work for me.

I wouldn't hesitate to run horizontal cylinder a little leaner than the vertical - I think it runs a little cooler.

Hope this helps. - B

[demontech]

floats should be set at 14mm off the big float, richen the pilot jet by one and the biggest thing- the needle jets on those wear out and go oval causing it to get slowly rich.
last is the float needle could be getting old and not sealing properly causing it to be rich.

[Jeff H.]

Welcome to the board Lechef! Hope you're able to get your FCR's sorted. You'll love them once you do. I had "tuned" myself into a big stumble at 4500 rpm when rolling on throttle. I just used BrianK's fuel/air screw settings as a baseline and got her sorted right back out. Thanks Brian!

Regards,

Jeff