my 450 is still giving me fits.. Ive done everything i can think of, compression is good, new plug 3 known good truck batteries and a jump box. The motor will turn over fine and run sometimes but 80% of the time it wont even attempt to turn over. i can pull the plug and it will turn over freely as soon as the plug is back in it does fine. I have a video of what it is doing put i cant find where to post it here. any help would be appreciated.