# Briggs 21hp over revving



## jhn9840 (Feb 26, 2006)

Hello all,

Have a 407777 0121-e4 030325 that is over revving upon start up. Put choke all the way on and it slows down to normal. Start to release the choke any at all the rpm’s shoot way up with a lot of black smoke coming from the exhaust. I’ve checked the governor linkages and the adjustment of the governor itself. It all appears to be functioning as it should. I took the carb apart and cleaned it out. There was some dirt inside, it helped a very little but was not the solution. Any suggestions are much appreciated.

jhn9840
John


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## Mickey (Aug 14, 2010)

John, here's my take. Not familiar with the model number so comments are of a general nature.

Suspect the butterfly valve is stuck open to some amount. The slowing down when choked is due to being over rich and additionally shutting off some air. As you open the choke more air is available so engine speeds up but is still over rich and that is reason for black smoke.

My suggestion is to check and make sure butterfly valve is closed up against idle speed screw. If that doesn't help, my next thought is there is a vacuum leak somewhere between the carb and the engine block.

Hope these comments may be of help.


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