Hi All,

My Sun Fli 4 build is nearing completion, now in the finishing stage. So time to start dealing with the engine for this thing.

The engine is a Jett 56LX, designed to scream at high RPM. Will do something like 17.5K RPM running a 10x6 on 15% nitro. It has the Jett-supplied tuned muffler, and it is all stock.

I am having trouble getting it to run right. I live in Denver at 5400 feet and so altitude may be the problem, which is, when the engine spins up to high RPM (or tries to..) it QUITS and then is flooded. So flooded that it takes several minutes before it will even THINK about starting again. All testing is being done on a test stand at this point.

Plumbing: pressure line from pressure tap on Jett muffler to tank vent. Klunk pickup in tank, line going from this to the needle valve, fuel filter, then carb.

What I have found out is that when I DISCONNECT the muffler->tank vent line, and richen the mixture some, the engine WILL run all the way to top speed without the quit/flood. Otherwise, with the muffler->tank line connected, the engine QUITS when I try to transition to full speed, EVERY TIME, and is flooded EVERY TIME.

This suggests to me that my problem is that the engine/muffler is developing too much pressure, which goes to the tank and then causes the engine to flood. What do you think?

It seems like a tuning problem, but I don't have any knobs to turn. What do y'all think is the best way to limit the muffler pressure going to the tank vent?