The first thing to check is the muffler fitting. Make sure that the fitting is clear of any obstructions. This is were your tank pressure comes from. Also make sure your clunk inside the fuel tank is not too long. The clunk should come close to the rear of the tank but not touch.

After that, if this is a new engine, start checking your idle needle. Don't screw it all the way in and start from scratch, just start adjusting it from where it is at. Do the pinch test with the engine at idle. It should stay at the same speed for a few seconds, then a small rise and then die. It is set from the factory on the rich side to begin the break-in process. After you lean it out some you should notice a more reliable and lower speed idle setting. After you adjust the idle needle go back and adjust the high speed needle setting the same way, but you should notice the speed rise as soon as you pinch the fuel line.

Also another thing to check is the glow plug. After you start the engine and get a reliable idle, when you remove the igniter, there should be no difference in idle speed or sound. If it changes, your glow plug is due for replacement.