Big red won't stay running

[Todd]

Got a 85' Big red that won't run longer than 15-20 minutes and then won't restart for about the same amount of time. It acts like the cap vent is closed but that's not it. I have flushed/cleaned both tank and Carb and left the cap off. None of the electrical components feel hot and although the spark is still getting to the plug it appears weak!
Any ideas of what this may be! Thanks in advance

[MountainRider]

If the spark is week when it's cold, then it's going to be even weaker (more resistance) when things heat up. You might check the resistance on your plug wire under both conditions.

[FullBore]

IS it Points or CDI igniton? if its points your capacitor is dead, if its CDi then I don't know.

Nat

[muskegnmud]

my guess is the ignition coil in the stator, same thing happened to me, you can test it and it will show good, replace it and your problems go away 8)