Heading to the Yamaha shop tomorrow for some yamalube
Thanks

I think "think i think" that if oil was the main cause then the piston would have seized before holing the top, which still looks like way too hot a plug for what you were doing. Just my opinion. Can't beat good oil though. Can't beat premix either, just inconvenient. I remember when workmate bought a new TD2 in "69 or "70 by memory--early 250 road racer. It ran 20-1 premix on Castrol R or Shell M but also ran the oil pump going 'full stroke' with no cable or anything to control it. Think they were worried about seizing on a closed throttle after a long flatout straight. Used to smell great & smoke the opposition behind lol.

When I got the bike it had a champion spark plug in it I left it without giving it much thought
Then the bike wouldn’t start turns out the plug fouled out so I went to the parts store and picked up a ngk br8es rode it around some then put in the castro two cycle and 10 miles later lost compression
Perhaps the champion plug was to hot
Anyways going forward going to run yamalube and ngk br9es plug
Thanks

I find the Trail Tech TTO spark plug gauge to be cheap insurance, it's also reassuring to be on a long climb and see temps rise then level off (hopefully) or I'll stop before it hits 400.

Yes this would be a great investment
I could monitor the temp closely
Today I drained the oil tank and added yamalube I think i will order one after typing
This message
Great ideal
Thanks

I also think it was not oil related but detonation. Does the old plug have tiny pieces of aluminium stuck to it? I would keep a good eye on the plug. A bore scope could also look in the plug hole at the top of the piston

Yes old plug had some fine particles on it
So far I have only put 12 miles on it since replacing the piston
Didn’t get a chance to take it out today
But I did pull the plug looks ok just a little oily I think that is for running premix plus injector oil
Hard to say what happened the bike is still on standard bore perhaps the piston was already falling apart before I got it
I will look into that bore scope you suggested that would be a lot better than pulling the head apart every hundred miles
or so
Thanks