87 Exciter wont run once warm

[BCrancher]

purchased an 87 exciter 570 from a friend recently. He didnt know too much about it, he just bought it with a trailer. he did tell me it was boggy at low throttle. It has the original mikuni butterfly carb

pulled the carb apart, cleaned and blew out every jet, nozzle, and entire carb body. cleaned the choke mechanism, and lubed the cable.

rebuilt the fuel pump with a new kit. replaced every fuel line from the tank pickup to the carb. I also replaced the pulse line from the engine to the pump. Installed new spark plugs, removed old gas, replaced with new premium.

engine has good compression, Im not sure of the numbers.

The engine will start first pull when cold every time. once I start riding around the yard for 5 minutes it wont idle without a little throttle. after that it wont start unless it sits for 30 minutes. Once i got it started again i tuned the throttle up to just before the clutch engages. The throttle was very responsive, I figured I had solved the problem. but after another 5 minutes around the yard it wouldn't idle without some throttle.

I might replace the choke cable next, I am up for any suggestions.
Thank you

 

[BCrancher]

I’m going to get a new choke (starter) cable, the housings are a bit damaged, maybe this is restricting the plunger.
I’ve been searching this problem, and found nothing specific to these Yamahas. Some ski doos and cats have said that coils start to fail after so many years, perhaps I’m not getting enough spark once it warms up. But that doesn’t explain why it still runs when under throttle. It just won’t idle the same.

 

[A couple of bucks]

Change coil and plug caps. The insulation in the coil is comprised and it gets worse when warm.
And the resistors in the caps have developed too much resistance.