nothing wrong with a good old points system [call me old fashioned or behind the times], not something like a broken valve spring or rings or blocked exhaust--had an old weedeater given to me that the exhaust was 'totaly' blocked at the outlet by a 'mason bee' nest. Anyway, only coming up with ideas as think you say you've not been inside the motor yet. Hope i read that right. worn out cam!!--had a tt250 with an all but totaly circular inlet lobe, ran but barely, & was quiet as back of the lobe was perfect where clearance is set. Goodluck.