I have a ford 800 tractor that won't start I've changed the plugs and changed the gas rebuilt the carb and nothing has helped I have been able to start it but the last time it started it took me about 20 minutes of turning it over and it ran fine once it got going but the next day it wouldn't start again if I try to start it now it will crank for about ten time and maybe chug a few times like it wants to start but it won't... its got a new battery any ideas please let me know I'm out of ideas I need help,, thanks