Scag (13hp Kholer) backfire ???

[Tool fool]

36" Scag w/13hp Kholer starts and runs fine until it warms up.
After 10 min. or so it starts to break-up. It backfires and goes I to a fit. I disengage the blades and it smoothes out a bit. I re-engage the blades and soon after the same thing happens. Eventually it spits and sputters even when the blades are not engaged.
I have no clue, But is their a timing chain involved that may stretch enough when warmed up to effect the timing ??
Any ideas on this ??
This is after a new tune-up (plug, filters etc...)
Thanks Ed

 

[EngineMan]

36" Scag w/13hp Kholer starts and runs fine until it warms up.
After 10 min. or so it starts to break-up. It backfires and goes I to a fit. I disengage the blades and it smoothes out a bit. I re-engage the blades and soon after the same thing happens. Eventually it spits and sputters even when the blades are not engaged.
I have no clue, But is their a timing chain involved that may stretch enough when warmed up to effect the timing ??
Any ideas on this ??
This is after a new tune-up (plug, filters etc...)
Thanks Ed

Check the coil (ignition) only way to be sure is to replace it, and check the valves, it could also be a bad battery so check it out also, and then the timing chain, you could also clean out the carb. and you say after the tune-up you may have a bad plug, worth you trying a new one again, you can get bad ones.