Re: CB750f #4 cylinder slobbering

Posted by RodneyCB750K1979 on Mar 06, 2013; 5:41pm
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/CB750f-4-cylinder-slobbering-tp4037429p4037452.html

Was the throttle and choke wide open during the compression test?  I think your compression is on the low side. Under 150 is poor.  Try some Marvel Mystery oil.  Low compression may also be due to poor valve adjustment/seats.  The cylinder firing with muffler off might be a symptom you're right on the edge of having enough compression.

Muffler resistance can leave compressed gas in the cylinder and at the end of the exhaust stroke when the intake valve opens, you could be blowing back through the carburetor.  But you checked the muffler flow and it appears ok.

On the intake side, how is the air cleaner and is the choke plate wide open?