Carburetor Rebuild - Motor Races On Idle

[anomie]

Hi.

I recently rebuilt my carburetor, the main reason was to rejet. The previous owner fit non-stock exhausts and the sparkplugs were fouled with dry soot indicating that the motor was running rich. I adjusted the pilot and needle for low and mid, I did not adjust the main (yet). I ran some tests and the sparkplugs look good now, a nice clean burn with no blistering or fouling. However, there is a problem (There is always a problem ). The bike "races" when idle after it has warmed up. It will race until I put it in gear, at which point it settles somewhat.

I had a few guesses on what could be causing this. These are my guesses:

1. The clutch is slipping, I don't have a lot of evidence to support this. The bike doesn't creep when I put it in first and activate the clutch. However, it is very difficult to get the bike into neutral after it warms up.
2. The carburetor needs to be cleaned. I didn't use any cleaner when I rebuilt, I just used compressed air.
3. The mixture is too lean-- Would this cause the motor to race?

Has anyone had this sort of issue before? I don't mind getting my hands dirty here, and I love to learn.. so any hints would be great. And any guidance to tell me if I am on the right track or if I need to add any more things to my above list.

Thanks folks.

 

[anomie]

I have read and memorized the carb guides

 

[fancyketchup]

Too much air will cause the motor to race at idle. If you havnt fiddled with anything else other than the carbs then I would start checking for air leaks around the intake boots/barbs if you have them.

 

[littlebill31]

What year bike, type of carbs??
Like Ketchup said, a lean mixture will make the engine race. Best way to check is to crack the throttle and see if it stays high, then drops down. If it does go high then drops after a second or two, lean. If it stays high, all the time, check the throttle stop and carb sync or for kinks in the throttle cable.
"1. The clutch is slipping, I don't have a lot of evidence to support this. The bike doesn't creep when I put it in first and activate the clutch. However, it is very difficult to get the bike into neutral after it warms up."
The clutch wouldn't cause this, but will cause the neutral problem. It needs to be adjusted, both adjustments.

You need to take them apart and totally, totally clean every piece when you "rebuild" them with air and cleaner.

By what process did you "adjust" the pilot? Did you change the pilot jet? And how did you come to this conclusion?

To get rid of a lean problem you want to check for air leaks. When those are dealt with, then you move onto the mix screw adjustment by using the "dead cylinder" method. After this, then you need to make sure you have the correct jet size for the pilot.

Carbs are controlled by throttle position, not engine speed. Each piece is a circuit. idle to 1/4 throttle=pilot. 1/4 to 3/4=needle. 3/4 to full=main.

If you read www.amckayltd.com/carbguide.pdf , then the answers are in there.

 

[5twins]

Do you have a points model with an advance unit? If so, then the advance unit may be sticking and the ignition may be staying fully advanced.

 

[littlebill31]

I didn't think of that.

 

[I am Carbon]

I know this might be over simplifying this but have you just adjusted the idle screw down after it has warmed up. If i start up without using the choke if idles at a lower rpm before it warms up. and I had the problem of the rpms lowering very slowly when I had the idle adjusted to high after it had warmed up. I lowered the idle and that stopped much to my surprize. also if your carbs are out of sync that will play havoc the idle too