DuraForce Mysteries

This is an interesting mystery:

If you've been following some of my threads, I recently took a DuraForce powerpack from a 10324 and installed it on a 10550.

When the powerpack was on the 10324, it surged badly. Once on the 10550, it ran better than any DuraForce I've seen. No surging, starts with one or two primes and has a lot of power.

What changed? I didn't take the carburetor apart. The only variable(s) here is/are a different mounting plate. I did install new gaskets for the exhaust and muffler and wiped out the muffler baffle.

Here are some hypotheses:

The carburetor was previously cleaned and I added Seafoam to the fuel which after sitting loosened crud from the jets allowing the carburetor to function better.

Changing the mounting plate, using new gaskets and cleaning the muffler baffle lessened restriction in the exhaust.


I don't know enough about the combustion cycle to really know which was the cure. I know it's not magic. But for future diagnosis of LB powerpack issues and general repair of small engines, I would like to know which road to take to cure these problems.

I now have the other 10550 I own where I removed the original carburetor that was giving me problems with hard starting. I put the spare carburetor on it, and now it runs good, but has the surging issue to a lesser extent. I increased RPM's about three clicks on the governor, and the surging has lessened to about 100RPM's/sec where it was at about 300RPM's/sec.

Also, the 8157 I have surges a little when the blade isn't engaged, but I haven't checked the carb yet.

If anyone has opinions or advice, please don't hesitate to pipe in. I think everyone would like to learn to cure the dreaded surge.