Originally Posted by kenh3497

Surging is normally associated with a lean condition. Are you running a fuel filter on the engine? If not you should be. Clean fuel is a necessity with YS's. Does the pressure in the tank hold for a good amount of time or does it go away in just a few minutes. Check the regulator diaphragm. If it is distorted, you might consider replacing it. Also check the plunger. In my experience a good cleaning usually fixes that problem. I have had to clean the regulator two or three times to have a satisfactory result. Flush the needle valve and fuel lines. While you are working on the engine it might be worthwhile to check the valve clearance for kicks and giggles. I like to use brake parts cleaner. It is convenient in the aerosol can and it evaporates fast so seems to be safe ,at least in my experience, on silicone parts. Some of the less expensive cleaners have a good portion of methanol in them. Just take a gander at the label.

Ken