It sounds like you just don't have enough lubrication. If you're using a so-called "R/C Car" fuel, you likely have a very low oil content in the fuel. Most "car fuels" have 12%-14% oil content, which is really too low for your engine. You should use a fuel that has more oil content. O.S. typically recommends that you use a fuel with 18% oil content or better. That's the same as "airplane" fuel...and will prevent premature wear of the starter shaft at its bushing.