Buy a couple easy outs for the screws in your chassis .They wont fit right off. Now take the size screws you have a spare or stripped and strip it. Ground the tip off the easy out"keep it cool or loose hardening" until you have to tap it in firmly. The best 3 bucks a piece I have ever spent, loaned them out a track more times than I have used them. You might still have to drill screws a little deeper some times. Left hand bits work well also but break too often.
Read some where to rub bar soap or candle wax into the underside chassis screw heads to keep the mud/clay out.
After run,after run ,after run ,after run, through the carb slowly , don't wash dirt into motor at the glow plug.
A bit of fuel tubing in some plug wrenches will hold the plug tip for easy install.