Motorcycle Repair: 6000 rpm on idle when the choke is one, carburettors, choke

Question
Hi Jim, I have a 81' Kawasaki KZ440 that starts up and runs great.  I have to apply the choke to start her up, which I've read is normal, but as soon as she starts up the rpms shoot up to 6k. Then I'll have to back the choke down to about 1/4 way for her to idle and warm up proper.  I've rebuilt & adjusted to carbs according to the manual. The synchronization screw was set & welded when I bought the bike so that cannot be adjusted.  Done all the basics...oil, air filter, spark plugs.  Any ideas?  Thanks.

Answer
6000 may be a bit high for the bike to run on startup but it is normal for the RPMs to shoot up with choke. Choke on these bikes is actually a fuel enrichment circuit through the carbs so you are dumping extra fuel into the motor to allow it to start cold. Too much extra fuel would cause this problem.

Another things to watch for with these bikes is to make sure there are no intake air leaks. If rubber intake boots are use, make sure they are in good condition or replace them if possible.

If the bike runs well off choke (stable idle, no smoke and good gas mileage) I wouldn't worry too much.