CB100 running odd

[cafecustom720]

So I've been working on this '71 CB100 that I got a couple months ago. I can get it to start but it does two things odd. #1: It will rev up sporadically and not want to settle back down to an even idle. #2: Sometimes it doesn't want to rev up from idle high enough to get it rolling in first gear. Usually it's after it has been running a couple minutes that it will have problem #2. I just put a new Mikuni carb on it and the jetting is good. I had hoped that this would solve the problem but it's still doing the same thing as it was with the old carb. The old carb had been rebuilt less than 100 miles ago so it should have been good to go as well. Any help would be much appreciated!

 

[VonYinzer]

Check for air leaks at the intake/carb gasket. Did you do any other top end work? Do you see oil seepage around the base or head gaskets? Have you set the valves correctly?

 

[cafecustom720]

VonYinzer thanks for replying. I feel honored to have a reply. Been following the work that you've been doing on here for a couple of years.
Leakage around the intake was something that had occurred to me after I posted this and I plan on checking tomorrow. I do have a little oil leaking out the case by the shifter shaft. Why would that cause it to have those symptoms?

 

[surffly]

Running a pod filter and or a cut exhaust?
Those are negatives to the small singles....

Sounds like an air leak though.

Real mikuni or knock off?
Why? Was there other work done to the bike to warrant the larger carb?

 

[Sonreir]

Verify timing (with a strobe light) and check valve clearances.

 

[VonYinzer]

VonYinzer thanks for replying. I feel honored to have a reply. Been following the work that you've been doing on here for a couple of years.
Leakage around the intake was something that had occurred to me after I posted this and I plan on checking tomorrow. I do have a little oil leaking out the case by the shifter shaft. Why would that cause it to have those symptoms?

Oil leaking out of the cases wouldn't matter (though on that bike you can change that seal without splitting the cases so... do that). I'm talking about possible air leaks in the combustion chamber. If that's happening it'll create a lean condition and the symptoms you're describing. The fact that it gets worse when warm makes sense as well. The metal heats up, swells and allows a larger leak.

Check the compression while you're at it. Also, make sure the carb gasket is in perfect condition and both mating surfaces are clean and smooth.