Topic: 1980 CB900C Hesitates

[Curtie94]

Hey guys new to the forum. I'm not sure if my bike fits but it's a 1980 CB900c has 85k miles on it.

It has been re ringed by the previous owner but seems to run strong. What I'm dealing with is that just off idle so cruising though town just barely cracking the throttle I get a hesitation. If I continue to hold it it will crackle.

I believe it is running lean since the plugs are gone white.

What I have done is rebuilt some low mileage carbs new accelerator pump properly adjusted and is working. I also replaced the Air cut off valves since they where all cracked. All new orings as well. Stock jetting.

But it does have a aftermarket 4 into 2 pipe.

The previous owner said he paid someone to adjust the valves not even 100 miles ago so I haven't checked the clearances yet.

I also found that I cant rev the bike under load past about 7-8k. I figured it might be due to the 3/16" fuel line I'm using so I haven't put much thought into that problem yet.

I adjusted my idle mixtures using a color tune and the outer cylinders run best with the fuel screws just about ready to fall out. The middle cylinders run best around 3 turns out.

Any ideas.

Thanks

Curtis

[beemerbum]

Nice bike, wrong forum

[Flyin900]

Move over to CB750.com forum as they specialize in your specific DOHC model and lots of very knowledgeable people over there. There is also cb750c.com which is the forum I am more familiar with as they only do the DOHC models.
You may have an issue with the slow jets or the actual circuit being partially plugged which is a common issue on those VB series carbs. The mixture screws are too far out and that points to an issue with the slow speed jet circuits

[70CB750]

Plus one on CB750.com forum.  Here is mine: