Guyscan you help a novice out with a conversion question. It's a Stihl 25CC that I bought from a guy that had already had the conversion mostly done. The only think I had to do was complete the spacer between the carb and the engine. I did as was told and dremmeled out a little channel to allow air or fuel to pass. The engine will run fine for one flight then it bogs down like it's not getting fuel on subesquent flights. It has a walbro carb but twisting the needles has very little effect. I cleaned out the filter screen but no better. Last weekend, I made a new gasket but have not run it yet. My question is, what is that spacer for between the carb and engine? I need to get another prop also. The engine is in my 1/4 scale cub. What is a good prop?

Greg