If the rotostarter slips, its probably the One-Way-Cluth (aka One-Way-Bearing) slipping on the starter shaft. Easy fix is hose the one-way out with brake cleaner or ether (starting fluid), reinstall with a drop or two of light oil (air tool oil is perfect) and lightly hand sand the starter shaft (ONLY where the one-way grabs, NOT where it goes through the bushing in the backplate) with 400-600 wet/dry sandpaper. Generally this will cure the trouble. If it comes back later on (short time span) then I'd be looking at the fuel I'm using and the amount of oil in it (or too rich of fuel mixture). High oil fuels cause all sorts of issues but one-way slippage is quite common with high oil fuel or overly rich idle mixture.
Hope this helps.
edit: if the carb doesn't flow fuel after you clean it out, tear the carb down completely. Remove the needles from the holders, remove the slide valve, and soak those parts in glow fuel or methanol for an hour. Blow the parts off with air (no air compressor needed here) and reassemble. A gummed up slide means the fuel circuits are gummed up too. Fuel or clean methanol will work superiorly compared to petroleum stuff. WD-40, or anything of that nature is not going to help you much.
Last edited by 1QwkSport2.5r; 03-22-2014 at 06:50 PM.