The engine of my m20 is running hot.Can the timing be to slow or can it be an exhaust valve not closing properly.It starts an idle normaly.This is my first rebuild and i haved checked the timing several times.
I would bet your mixture is too lean. Check your float position. In my experience, when they run hot, they're really HOT, keep in mind these side valves do tend to run hotter than OHV engines.
Timing
All gaps (points and spark plug)
Use an un-suppressed plug cap
Don't use a plug with any resistance
Check the HT lead
Clearance on the valve lifter, and that it frees easily
Check valve clearances, especially the exhaust valve clearance
Lap the valves in
Check the mag pick-up for resistance
Make sure that there is a good seal between the carb flange and the barrel
My bike was running lean and hot and was totally transformed by fitting a brand new carb and a new mag pick up.
