Topic: carb jetting in relation to porting cyl. head 1978 550K

[rsvp9146]

I'm just about ready to get the head back on my 550K and was looking at the intake and exhaust ports. Seems there's a lot of rough casting marks in there. I was thinking of taking my Dremel and cleaning them up a bit. I was wondering what this will do to the stock jetting on the carbs.

 Can I use the stock jetting if I just do a small clean-up? I really don't want to get into messing with the carbs too much. I imagine I'll need to richen the mixture a tad to compensate.

 Has anyone had any success doing this? Any info would be great

[mlinder]

Unless it's going to be pulling a LOT more mixture in (to where the stock jets can no longer feed enough fuel into the mixture) you should be fine.
Remember, Intake ports should be left a bit rough, to keep air flow turbulent so that fuel does not 'pool' on smooth surfaces.
Turbulence keeps the main stream of the mixture AWAY from the walls of the intake.
Exhaust ports can be smooth. Want it to exit as quickly as possible.

[TwoTired]

Porting and polishing are to make the engine breathe easier at high RPM, by offering less restriction to air flow.

Turbulent intake runners improve cylinder efficiency at lower air velocities.

Each of the two concepts has it purpose, and the choice of which one, is made given the intended use or goals.  Where in the RPM band do you want your power gains?

Jonesy did a port job on CB550.  But, I don't recall if he got the jetting straightened out.  You can search for his porting thread.

Cheers,