well I was all stoked to get my 310 big bore kit and go to the oregon dune (Horsfall) it ran awesome over in medford and then when I got to the coast I blew it up in an hour and a half. I am pretty sure it was a jet problem. I am running a bigger than stock jet but apparently it was not big enough. I ended up melting the front of the piston.

Anybody with experience on 250r's and the coast can you please tell me what jet size you are running? and not have any problems on the coast?

 

wow, nobody wants to reply? or nobody knows??

 

Is this a resleaved stock cylinder? Was the motor fresh? Did they not chamfer the exhaust bridge properly? What jetting in what carb? Did you go down in elevation without rejetting? There probably another 50 questions I could ask, why don't you just list the specs on the motor and riding conditions when it siezed

 

Sorry, I guess that does need to be said.

Ok, I bought a big bore kit from a guy back east. He said the piston was ran once, for maybe an hour. The jug is brand new, never used, from ESR (Eddie Sanders Racing) and the piston had a couple of hours on it. New cool head and new TRX6 pipe from ESR. The Keihin carb is a 38mm with a .176 jet in it. This jet has worked great for me in the past but on my 25mm carb. Not knowing any better I used the same jet. I mix the fuel at 50:1 with MC-1 synthetic. Conditions were warm, say high/mid 60's. I was in 3rd gear going up a dune when it went out. Only was out on the sand for about an half hour. The top is end is primarily new, the bottom end was done 4 years ago. When I had it all running here in medford it sounded fine, ran great. but when I got over to the coast and started it up it was ideling but when you gas it it sounded like it was starving for gas. but once it was at high rpm is was fine. Medford is about 1200 feet above sea level.

That is all I know about the top end. I have been looking things over and I also believe my plug is too hot for what I have now. I run a bre-8 plug. in my last setup I was always fowling plugs so I went up a plug.

I was just curious as to what everybody else was running and how big of a jet I needed to go to. I know what my problem was.

 

Your jetting maybe slightly lean, maybe spot on, you really should have checked it especially since you went down 1200' in elevation. Did cut out while riding? If it did what was the throttle position. Could have been numerous things, Lean , air leak, Stuck float causing the bowl to run dry. Did it rev up before it seized? The BR8E should be fine.

 

thats just it, it ran fine when I was moving. it just bogged down when you first apply gas from idle until you gave it throttle like it was trying to run out of gas. then the rpm's went up and it sounded fine. How was I to check it before hand? When I was getting on it it did not cut out, it ran/sounded perfect. as I was going and it died, it just died, no high idle besides what I was appling. actually I was coming down from the high idle cause I was turning on the hill. it just quit. it never seized as I was able to kick it over when it died. I know it was lean cause it was not blowing white smoke any time I was over there, just the very first 3 minutes of starting it up when I first got over there. It didn't hit me until it was too late. like I said, it happened fast. Being the novice I am to 2 cycle engines I did not know the signs of it going south. but I have been riding for 10 years on it. never had a problem like this though.

 

so know body has a 250r and run a big bore kit???

 

well I have found the problem since nobody is willing to help on this forum.

ESR suggested my pilot jet be at least 50. the one I got from the kit is a 35. problem fixed.

 

A 50-1 mixture is very lean.. Try 32-1 or 40-1 at the leanest. You will lose some performance but enhance the reliability by 10 fold..

 

so you are saying instead of 1 12oz oil per five gallons I should do like 16oz? the oil I mix it with says right on the bottle 50:1 is best, 1 12oz bottle to five gallons.