[Johnagain]

Sounds like you might be dropping a coil. Pull one coil wire at a time when it starts acting up. If it dies when one wire is pulled then you know it's the other side that is going bad.

 

[Johnagain]

I mentioned before that when the engine warms up, I see a drop of oil from the screw of the exhaust manifold of the back cylinder. I wonder if that head gasket is causing the loss of power.
I am frustrated with this engine.
I'm thinking of resealing the old one or re-powering with a Briggs.
We'll see tomorrow.

You're frustrated because you won't even do the first thing in trouble shooting your engine. You were asked to test the coils on the second post of this thread. You still haven't done that and we still don't know what's wrong. This is why the few here that help others with correct diagnoses have problems with backyard mechanics that have no idea the correct way to diagnose the problems that we have trained and worked with for many years experience. Yes we make mistakes and aren't always correct but the problem is not right in front of us to diagnose. Eyes, ears and smells are part of our trouble shooting that we do not have in this situation. All we ask is that the person with the problem follow through with the very simple tests that we ask to help them fix their piece of equipment before jumping threw hoops from people guessing with all these crazy ideas that might be causing the problems.
My rant is over. Good luck with changing all the unneeded parts to your engine.