So on my buddy's 1980 340 Yamaha Enticer there is this weird issue.  It was running poorly, so I went through the carb and cleaned it- all good.  The only thing it has now is this:

When running full speed and you let off the throttle, it ends up dying.  You can sometimes recover it by feathering the throttle, but it just acts fuel starved, bogs down, and about half the time, dies (if you can't recover it by feathering the throttle).  Once you stop, you give the cord a pull and it fires right up.

Any ideas?

are you sure there isn't some crap stuck in the pilot jet?

How long will it run at full throttle? Is it a vacuum fuel pump?

An "out there" item...

Fuel pump diaphram leaking into the vacuum port / case of the motor?

There's a fuel filter in the tank on the pickup.

Have you checked the mixture by supporting the track and going WFO for five seconds then killing the power? Pull the plugs and make sure they are chocolate and are the same tint. Have you tried new spark plugs? Sounds like a small air leak but with a 2 stroke it can be several issues. Is the enticer a single carb setup?  After checking the mixture I would look into that air leak especially to the fuel pump. Also double check the float level in the carb(s). Make sure the needle and seat is good, the needles will eventually wear and a ridge will show up on them. Check the needle in the slide as well, make sure its anchored and not floating up and down in the slide.

Possibly a leak between the chambers in the fuel pump? Or an air leak between the case and the pump? Floats set wrong or an obstruction at the inlet?

I'll try some of the standard intake leak checks, and take a look at the diaphragm fuel pump.  I'll let you know what I find.   Thanks guys!