Since you got the engine used. Some people take the baffle out of the muffler for more power which would reduce muffler back pressure and also pressure to the tank. If after you try everything else and still not get it running right and find that the baffle has been removed. You can stick a little steel wool in muffler to increase back pressure. Shouldn't need much.

Never used the steel wool trick myself, but have read about it numerous times. Also have read numerous times about the baffle being removed in that engine.

Hope you find the issue. They are a decent running engine. I have one, but haven't modified it yet.

Good Luck