Recently finished a top end rebuild. Fuel on. Choke on. Engine starts and runs well. Initially at about 2,000 revs.
However, release choke and revs rise and climb to 4,000+ and won’t come down.
???
3 Feb. Update. Carbs out and checked. Idles screws balanced.
All cables checked and oiled. I did find throttle cables were occasionally snagging.
Now all running well and smoothly.
Thanks all for your suggestions.
Do the slides close fully? Slides in correctly? Cut out to intake. Back off the idle adjuster screws as a start. good luck.
Are the throttle cables tight when the throttle is released? You should be able to lift the cable out of the adjusters on top of the carbs by about 1mm on both sides.
When you open & shut the throttle, do they both close together? Listen for the clicks as they shut.
Is it cable choke? Cable tight for cold start & relaxed for normal running.
You don’t mention if you did anything to the carbs. If not, the throttle(s) sticking open is probably the most likely cause, as already mentioned, but I would also check for air leaks between the carbs and the rubbers, rubbers and heads, and splits in the rubbers. Of course the engine can’t reach 4000 rpm without air and fuel, and if we assume the slides are closed, then the air must come from elsewhere. However, I agree with the others that the slides not closing is the most likely explanation, so would try cable runs first. The cable(s) may not have engaged properly in the recesses where they enter the carb. for example….