Poulan 46 on ignition. Battery, switch check out good.

I have a conversion engine that is surging/cutting out. It idles well, but when the throttle is advanced (fast or slow, worse when cold) it starts to cut out. It never goes dead, and starts easily. It is worse in the air than on the ground. I can lean out the low end so that it almost goes away, but the engine will die if left to idle too long. If adjust it and seem to be running well at top end and take off, the surging returns after about one trip around the pattern, albiet less severe. Never dies, not once.

Gaskets and diaphram seem ok. Fuel draw seems ok. The carb is pressurized via a tube from a bypass port to the top of the carb, and the pulse hole in the body of the carb is closed off. I made a new gasket for the base of the carb and remounted it on the engine. I cleaned everything I could get to. The engine was run a good bit with this setup without issue.

I was going to check the idle jet passage(s) and removed the low speed needle. There is a grey plastic "washer" on the straight part of the needle above the tapered section--before the threads. The washer has a step in it. Is this the "seat"? Should it come out when the needle is removed? It fits very tightly at the top of the shaft of the needle. Since I can't lean it so that the engine dies when given throttle, I thought maybe this has come out of it's seat in the carb body, and is passing way too much fuel to the carb. The high end is not bad, 6750-6800 on a Pro Zinger 20-10.

All the Walbro pictures I can find have too poor resolution to get a good look at these parts. This carb is "enviromentally friendly" and is not on the Walbro site as far as I can find.

Any suggestions appreciated.