Running rich below 4000 RPM - 1974 CB750K4

Posted by CR125Honda on Oct 31, 2012; 4:36am
URL: http://vintage-and-classic-hondas.81.s1.nabble.com/Running-rich-below-4000-RPM-1974-CB750K4-tp4031469.html

1974 CB750K4 - OEM carbs, exhaust, air filter & airbox

I've had a rich running engine (from idle to about 4000 rpm, runs clean above that) for a while now and haven't been able to pinpoint the issue.

Thought it might have been a ignition issue (original OEM coils that didn't pass the resistance checks) so I installed new Dyna S ignition system with new Dyna coils and Dyna wires. No change...

The springs on the OEM spark advance are a bit weak though. When checking the timing with a light, the timing is spot on a higher rpm but doesn't return all the way to "F" at low rpm. The advance moves freely, no binding. Thought about cutting off one coil on the spring to stretch it but haven't done that yet. New springs are "unobtainable".

Air bleed adjusting doesn't help.

I've cleaned the carbs a couple times (checking all passages, soaked the jets, correct float height, etc.).

Thinking the previous and original owner may have reamed out the pilot jets to clean them (the bike sat for a while before I purchased it) I just bought a set of Keyster carb kits.
Planning on rebuilding the carb with all the pieces in the kit (pilot, main, air bleed screw, jet needle and float valve needle and seat).

When I took the Jet needle out, I found it on it's highest setting - of the 5 clip settings on the needle, it was at the fourth one down (closest to the taper side of the needle).

Looked through all the manuals and couldn't find the OEM clip setting. It it the 4th clip position or is the middle setting correct?

Also read in another post that some are having issues with the Keyster Jet needle.  
Is that correct?
My old needles "look" good. i.e., no wear marks on the taper. Should I just reuse them?

Thanks in advance, Ken