Re: Carbs!

Posted by LukeM on Jul 20, 2011; 12:51am
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/Carbs-tp3184034p3184142.html

Do the spark plugs look black and sooty, or black and shiny? Black and sooty usually means it's running rich; black and shiny means there's some oil getting in there.

Pods will allow more air through compared to the stock airbox/filter.  This means leaner operation.  Same with opened up exhaust vs. stock.  Less back pressure means more airflow = leaner operation.
It's possible that someone put in bigger jets to compensate for that.  In order to find out, you will need to remove the carb bank and check the jets.  Also, check the accelerator pump. Maybe it's leaking or pushing fuel all the time.

My Haynes manual says the primary main jet is a size 68, and the secondary main jet is as follows:
CB750F pre-1980       size 98
CB750F post-1980     size 100
CB750L and CB750K  size 102

Pilot screw factory setting varies between 1.5 turns out from all the way in, to 1.875 turns out. Consult the FSM to find your settings, and start from there.  I think the mixture gets richer as the screw is backed out.  So if you're running very rich, I'd turn one of the pilot screws in, counting the number of turns.  Hopefully the previous owner set them all the same way.  I'd start with 1.5 turns out, and adjust from there.

Good luck, and keep us in the loop.
Luke M