I don't know about that Turbo-Jett muffler that you are using, but I do know that the Bisson Pitts style provides marginal back pressure. The normal fix is to plug one of the two exhaust stacks. If the muffler that you are using has two, I would suggest plugging or restricting the exhaust to provide more back pressure. The stock OS muffler has only one exhaust stack, and the engine runs fine on the designed muffler.

I agree, chuck the pump and keep it simple. The less complex that you can keep your system, the more reliable it is going to be. You simply need more back pressure.

> Jim