I have a 95 foreman. I purchased it with the motor in a box. It used to have a 500cc piston and cylinder kit but I have replaced it with a stock cylinder and piston. I have replaced the hot cam with stock. I have rebuilt the carb with stock jetting. It has a honda stock airfilter with box and snorkle and stock exhaust. I have lapped the valves and installed new stem seals. I have adjusted the valve clearance to book values. Compression and leak down test good. Timing appears right on. I have taken it to two reputable shops and both failed to fix. It will start easy but quickly turns the exhaust pipe red and "coughs or spits" out the carb one out of every five times it fires at idle. Eventually, it will "cough" hard enough to stall. It does the same thing with or without the muffler. The head pipe is clear. Any suggestions?