Originally Posted by
Sport_Pilot
It can also be an undersized fuel line. It collapses under suction, engine leans out, suction reduces, line opens up, engine goes rich, suction increases, then line collapses again. It has happened to me before. One time the line wasn't so much undersized as it was a very thin wall. It was an unusual sized line that came with the ARF fuel tank.
This isn't the issue I'm having. I used two different tanks - one of which I used to use on the engine (though I replaced all the lines inside and out) previously which is setup for both regular venting and also Uniflow. Either setup fave identical results except the Uniflow caused fuel to shoot into the muffler after dropping the throttle from WOT. I'm using the same muffler, fuel, glow plug, carburetor, and test bench. I tried no nitro (80/20) and 5/20 fuels. No change other than more power using a little nitro. I might be able to try running it tomorrow or Thursday to try some different things. I have a half dozen engines I want to run before it snows and this engine I want to have sorted before winter..