I got this saw as a box of pieces which I attempted to puzzle out. Put in a meteor piston, it will run on prime, but it won't stay running. (I've already rebuilt the carb and replaced fuel line) Don't know if it matters but I suspect I'm missing a piece. On most old stihls ive seen a metal ring that slides over the carb bolts and supports the intake boot? This saw did not have that, do I need that and if so, does anyone know the part number?