If the carb isn't the culprit you could have a weak coil or wires. As the engine heats up resistance increases and the spark gets weaker causing the plugs to foul. Just a thought though, check the carb first.

 

I agree with John.
Change your plug wires, esp the rear one. I believe your problem is electrical now.

BTW John, Thanks for the info about Mikuni choke goes off w/throttle. I didn't know how it KNOWS. Seems like it doesn't hurt anything leaving it on, goes off when I start getting up to speed.

 

Actually I am paid by Mikuni to run all over the world and push them off when you aren't looking!!! LOL, It keeps me quite busy and gets me lots of frequent flyer miles!!!:-))

 

That's funny....LOL!
I've actually been thinking of going back to a S&S E for some better mileage.
I had one yrs ago and got good mileage, besides I like the SS air cleaner look.

 

Update: replaced enrichner cable, I don't think it was fully closing, plastic broke behind nut on threaded portion. So far so good, haven't fouled a plug yet.

 

Glad you found your problem and reported it here. We all have another thing to look for if we have your problem. I know I will be sure and check my enrichner if my plugs start fouling.