ok u say it starts 20 times in a row and then wont I need more info the time it don't does it try to start is it cranking? If it's the 4Y the wire breaks are common but not with these symptoms it sounds like it could be as simple as a starter on the way out. Also check for voltage drops across both Neg and Pos from bat down to bat also next time it don't start try wrapping the starter. Large volt drops across either Neg or pos will cause starter to fail premature. If still won't start shut gas off? Drain LPG from line. So system is dry. Remove the two 10mm bolts over the carb. That connects the hose from the air flt. Get a mechanics rag wet a little with gas and see if Ur engine will fire that will tell me if its Ur engine or a fuel problem real ez test also may want to run ur engine and with the hood up u may want to pull the drain plug that's a 12mm pain to get to if it's ur first time pulling because u need to do it hot pull the over fill reservoir out for more room don't drop the brass washer and don't over tighten not strong medal and when it don't start is it first thing or is it after it has been running a wail