Well the title says it. My story starts with an MC28 with a 300 kit. So I've put about 1500mi on the crank and 250mi on the top end this year. Was running great and I went to switch domes from rocket fuel to pump fuel because its putting me in the poor house. Found a dent in the lower piston ( the one that always blows up?) TYGA sent a new one right out. Put it in went up one main. Making the front 2 sizes richer than the back. Did one heat cycle and headed to the track. First 2 laps nice and easy under 10 grand. 3rd lap full throttle 4th gear (pop) on the straight.

So I checked the compression it was 0. I knew it wasn't good. Later inspection revealed a hole almost the size of a dime dead center and tons of detonation marks or marks from pieces of piston around the squish band.

I don't belive it jetting because it went 250mi on 117oct and loved it. The rear looks great.

I am going to do a leak down test when my $188 piston gets here.( yeah the US dollar sucks and its comming from thia moon)

The only thing I can come up with is an air leak or ignition problem?

The pickup coils are tight and in the right spot. All connection are good. The top cylinder is good so that should cover shared ignition components.

I unfortunatle didn't do a leak down test before I tore it down.

I know this is a loaded question and only a few will be able to help but, if I spend another $600-$1000 for 2 more laps I may sell the NSR. I said I was going to last time but I talked some sence into myself.

Thanks,
Jeremy
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1995 A kit TZ 250
1994 Rothmans NSR 300sp SOLD
1998 RM 250 freestyle/motorcross
1998 Meathanol burning CR 500 AF super retard/motorcross/sand dunes/play bike