This motor has run great in the past. Starts right up and idles for ever. All of a sudden it is doing this... it sounds like it does when it starts to run out of fuel. (leaning out) I haven't touched the needle settings at all. But it is doing this all the time on a full tank of gas. Reving really high and sputtering. If I trim it down to a slower idle it dies. I looked for cracks in the fuel tank and couldn't find one. What am I missing? Thanks

Try adding a little more to the LSN to bring down the RPMs. But before take a look at the backplate and heatsink to make sure they are on nice and snug.

How long have you had it? How much fuel has it seen? What are you doing differently from before?

Sounds Like an air leak.
Did you check your fuel line?
Did you check your pressure line from exhaust to fuel tank?
Bad Oring inside fuel tank lid?
Check exhaust gasket where header mounts to engine.
Check exhaust coupler from header to pipe.
Is Glowplug tight?
Are Head bolts tight?
Did you seal the engine with silicone sealer?
Orings on high and low speed needles could be torn!