My new 1993 CB750 and carb issues

[Yorgi]

Hi!  Bought a 1993 Nighthawk 750 w/ 9K miles.  Got it for just 2k bucks cause it has minor running problems which I am now attempting to deal with.

Leak valve cove gasket, new gasket no problem.

When you start it up it goes to a nice idle when cold, but it has a bad flat spot with the throttle off idle. If you play with the throttle like mad and get past the dead spot and get the idle up past 3000 rpm motor acts normal all the way up.  I can drive it that way but I have to be prepared to rev, rev, rev til the tach gets to 3000 and I’m at speed on the highway.  Then if I drive 5 minutes and motor warms up, when I come to a traffic light and stop the problem is gone and no more off idle flat spot.  But sure enough if I stop for 10 minutes and shut off the bike the same startup fight begins all over again until 5 minutes into the ride.

Just got the carbs off, looks pretty clean. But gonna clean the jets, install the needle washer mod (had that same mod in my original 1981 750k) and probably do the exhaust mod.  Also planning on draining the tank, rebuilding the petcock and installing an inline gas filter.  Of course if I put it back together and it’s the same I’ll go with the latest SEAFOAM treatment!  I read on the forum about  1 gallon of gas to ¼ can of Seafoam and the 3 day routine to cleaner carbs.


Thanks for the great mod articles and all the interesting threads.  Will keep you posted!

[cmyers]

Sounds like you already have a good idea of what you've got to do.

I wouldnt claim to be an expert, but I would suspect the pilot needles might be clogged. I would guess that with the carbs off while you are cleaning the jets and floats if you make sure to clean the tiny holes on the engine side of the carbs, look just below the slide, and then run seafoam you it would take care of your problems.

[ariwhiteboy]

Choke passage clogged?

[cmyers]

Choke passage clogged?

LOL...cant believe that I couldnt think of the word Choke when I referenced the "tiny hole in front of the slide."

[82CB750SC]

So, any improvement since we last heard from you?  How'd the seafoam and the washer mod work out for you?