you definitely need a temp gauge if you don't have one yet and get some temp readings. your next thing would be to make sure your glow starter has enough juice to heat the glow plug. even if it glows, it still can be weak. the last thing is how many gallons of fuel have ran in it? and was it broke in properly? the engine could simply be needing re-sleeving. combine a warm engine with an already too loose piston to sleeve clearance, and it could not be getting enough compression to ignite the fuel.