Need advice, 1971 125 f6 ,, Have rebuilt the carb. Cleaned it twice.. Replaced the crankseals, when starting , the idle races up, wont idle normally.. Help..

 

Gotta love old bikes...
I would drain the carb bowl (unscrew the bottom drain) and refill. Just turn on the petcock, let sit for about 10 minutes, start it up. Sometimes the float gets wacky after a cleaning. (Double check your throttle cable for binding; attachement points, lube, etc.)
Keep us posted.
Glad to have you with us, T.

 

Sounds like a lean prob. Might have an air leak somewhere. How are the carb boots? Cracked? Shrank? Not too familiar with the f6's. Spray carb cleaner around the carb when running and see if that makes a diff. Idle speed not letting it idle down?

 

As mentioned above, "racing of the engine" can usually be a simple loose fitting or cracked "old" boot. Since you have replaced and rebuilt the carb, the air leak would be a good guess.

 

I cleaned the carb again , drained the bowl and let it sit.. Now the bike won;t idle but will run above 4000 RPM.. Any Ideas.. Thanks