861/ 172ci gas surging problem

[William Fissell]

I apologize in advance as this is a followup to a thread I cannot find . 861 w 172ci engine recent new manifold as was cracked. Rebuilt carb and checked all passages w guitar string. Runs fine for a few weeks and now theres a fair amount of surging. I posted a while back asking about governor compensating spring adjustment and I followed the I&T manual instructions. IIRC in the prior post it was suggested to me that the idle circuit was to blame. Surges - slows down (doesnt stumble, just slows) revs and slows about 15-20 seconds per cycle.
- plenty fuel out the line and carb
- pulled carb and rechecked all passages clear and clean
- varying mixture didn't do much

Any suggestions?

thank you in advance

 

[showcrop]

We don't know how much is "plenty of fuel". Did you perform the standard flow test?

 

[William Fissell]

Yes. Initial surge and then the same steady flow thats about 1/2 cup per minute, same as on every other.

 

[Sean in PA]

I've never had to measure, but some folks say that you need a pint in 30 seconds, while others say a pint in about a minute. That's 4 or 8 times more flow than you claim that you are getting depending on who you listen to.

 

[showcrop]

I've never had to measure, but some folks say that you need a pint in 30 seconds, while others say a pint in about a minute. That's 4 or 8 times more flow than you claim that you are getting depending on who you listen to.

I have been taking note of posts about the test here for a few years and have been seeing a pint in two minutes. So depending on the RPMS and load when William is having his problem, he could be running short of fuel.

 

[William Fissell]

Ill check again tomorow- just cleaned carb and will reinstall. I dont think its a fuel flwo problem but OTOH her I am askign for help dumb to not take the advice im given

 

[MarkB_MI]

Since you recently replaced the manifold, and it worked fine for a while, I'd be looking for a vacuum leak. Make sure your manifold nuts/bolts are still tight.