Topic: Surging problems on 1981 650c

[redaccent]

I'm having surging problems at 5000 rpms on my 1981 Honda CB650C.   I replaced the carbs with rebuild ones.   It ran fine before the carb change out, but I wanted a rebuild set because of leaking.   It runs very strong up to 5000 rpms and then it sputters.  It has a 4 into 1 exhaust and a OEM style KN filter.  I'm wondering if I have crud in the carburators, I just put a fuel filter in it because the tank had particles in it, and it made the floats stick.   I flushed them out and it seams to work.  Or if I have to rejet the carbs because of the carbs are different than the original (the carbs are 1981 carbs but it has OEM jetting) and the bike has 4 into 1 exhaust.

I will try the Seafoam cleaner and take the bike out today.

John

[redaccent]

Also do you think its the air mixture screw needs to be adjusted.  I have looked up on this site and it said 2 1/2 from soft seat.   Let me know if this right or is it non adjustable.   I look it up on the Clymer and it didn't have any information.

John

[Gordon]

Your first post is a little confusing.  Are you saying the original carbs had been re-jetted to compensate for the 4-1 exhaust and K&N filter, but the new ones haven't? 

If the originals worked fine except for leaking, why not just fix the leak?

[Soos]

I'm assuming you have a CV head and carbs.

First, if your fuel was dirty enough to affect your float needles, you NEED to remove the float bowls, remove the slow and main jets, clean them and any other passages you can find while you are at it.
Be careful, remove ANYTHING that can be damaged by compressed air or carb cleaner.

I believe your slow jet it pressed in though, it WILL come out, although your manual will say it is not. A pair of pliers and a twisting motion. But BE CAREFUL. break one of these, and i believe they are non-replaceable mostly.(used bits from others/e-bay?)


l8r

[Soos]

I'm having surging problems at 5000 rpms on my 1981 Honda CB650C.   I replaced the carbs with rebuild ones.   It ran fine before the carb change out, but I wanted a rebuild set because of leaking.   It runs very strong up to 5000 rpms and then it sputters.  It has a 4 into 1 exhaust and a OEM style KN filter.  I'm wondering if I have crud in the carburators, I just put a fuel filter in it because the tank had particles in it, and it made the floats stick.   I flushed them out and it seams to work.  Or if I have to rejet the carbs because of the carbs are different than the original (the carbs are 1981 carbs but it has OEM jetting) and the bike has 4 into 1 exhaust.

I will try the Seafoam cleaner and take the bike out today.

John

Seafoam is a good choice, but not needed yet i'm thinking.
Don't worry about re-jetting yet, get it to run good first.
It may be a tad rich or lean, but it should be able to at least hit 95000 rpm unless something is really buggered.

Your bike puttering out at 5000rpm is indicitave of main jet(s) plugged/partially blocked


Good luck.

And if you don't want to /are unwilling to remove the bowls... or are just plain lazy, and want to try a easy trick...

Pull your airbox back, and put a air hose into all of the air jet orifices on the intake side of the carbs.
My father in-laws yemeha 550's #1cyl carb gums up, and that is his fix at the beginning of the riding season.
That and a tank or two of seafoam.


l8r