SR250 losing power at high rpm's

Hi guys ,

Ive been working on my bike all winter long. It finally looks like I want it to and now Im having engine problems. While riding when I get to high RPM's ( 40 mph 4th gear ) the bike starts to cut out and buck. It will be fine then stumble as it rev's up. It does this in neutral also.

Here is what Ive done so far.

pulled the carbs and cleaned them, also took air compressor and blew it all out.

changed the main jet - no tears in the diapragm all rubber was good

check for a vacumm leak and it was fine

pulled petcock and cleaned it

cleaned tank and put new gas with treatment in it

had battery tested today and was fine.

new spark pulg when this started ( spark plug is now turning black ( not oily ) )

I did notice when reving it up in neutral in the garage the headlight cuts in and out like the engine. When I first got it running I had a spark/short in the starter relay but dont know if that would cause it. I dont think its a fuel issue as Ive check everything to do with fuel. Anyone have any suggestions? Possible electrical ?

Thanks for all your help in advance.