View Full Version : Terrible weekend......

10-21-2002, 08:07 AM
Oh this is bad, took my 83 250r out for a blast with my brother. Everything was going great until I cooked the top of my piston.

WAIT WAIT, this gets worse, it happened when my brother and I were racing side by side. He has a 350x, will I ever live it down? All I heard over and over was "that's what you get trying to keep up with a 350x with a little girlyman 250r"!!

Seriously, what would be the most probable cause for the top of the piston cooking, it looks like one edge just melted and seized the bottom ring as well? Any ideas? I had just mixed the fuel that morning and I know for a fact that it was right.

Replacing it with a Weisco piston, should I oversize? Not that I need to oversize to keep up with the 350x's


10-21-2002, 03:20 PM
Most likely cause is running too lean. Not the gas/oil ratio but the fuel/air ratio by your main jet.

Anytime you cook a top end you can be almost certain you will need a bore job. Have it bored to the next increment, and when you get it back, take frewquent plug readings until you get the carburetion setup right.

10-21-2002, 03:30 PM
Kind of what I thought but how do I check for correct mixture? I sure don't want to blow up another one. Could this have anything to do with my reeds? Thanks for the help.


10-22-2002, 09:53 PM
i have an 84 250R, its pretty much the same as an 83, and this has happened to me before, when it was on its stock bore, i never did know why it happened, i always thought that it was because i was pushing it too hard in one gear and not shifting soon enough, but ever since i bored it .20 over and put a wiseco piston in it, it runs great with no probs,...i never did know why it happened..maybe the same reason as yours....idk...

10-23-2002, 08:17 AM
I brought the head down to have it checked. I guess there was some damage to the intake ports and they have to bore it to .50 over, it's never been touched so I will be able to get away with it. I'm almost scared to see how sick it will be. I would've rathered not go that much but oh well. Did you piston cook more on the exhaust side as well? I hope this is the end of it, with the gasgets, piston, pin, bearing for the piston, new reeds and the bore it's costing me almost 4 bills, sounded high since the last time I had it done but I need my wheeler.

Thanks for the feedback.