i have an 88 trx250r, found out it was bored 80 over. ordered a new 80 over piston and rings, cylinder is good just needs honed. question is should i bite the bullet and put a thinner head gasket (cr 250)? i have a feeling comp ratio is already spiked due to piston size, but i must go faster. anyone think i should decide against it? also i must buy a new carb, im thinking about a pwk air stryker 38mm. will motor perform better than the 34mm or not? i forgot to mention there is some port work done to the head. please give me some input........................thanks

 

i would go with the thinner head gasket it shouldnt hert at all just run the premium gas with octain booster in it and your motor should run great also with the high proformance 2 stroke oil like the maxis or something


about the carb i would go with a mikuni or something like that i like the flatslide carbs they work great no problems out of mine since your bored and everything like that you might would want to go with the 38mm sounds good to me!! and since its ported and all but just call carb parts warehouse or some place like that and they will hook you up wth everything you need jetting and all well they send extra jets just incase there alittle off!! i dont have there# but they are in dirtwheeles! they are located in the ohio area i think

well that should solve everything

 

Here my advice..

Run the Cr head gasket. I have had MUCH thinner (like a piece of paper) for a head gasket on my stock cylinder. Before you start it take a compression test. If its over 188-190 you will need to add some octang. Dont be cheap and buy octang booster! Buy some strait "race" fuel, (something like vp-red, or anything over 102 octang) and mix it with strait pump gas 60/40 or 50/50, and you will be safe. This might sound complicated but you will get the hang of it. Remember, you only have to do this if the compression is over 190# on the guage, and honestly it probly wont be but test it anyway. The PWK A/S 38mm carb is an excellent carb. Far better than any mikuni IMO. Easy to tune and is a good overall design. The diffrence from the stock carb is unreal.... By the way, your porting wont effect compression much.

.... Also, if you ever want to get a LITTLE bit more power out of it, AND it has 190# or over you can buy an adjustable timing plate and advance your timing 2 or 3 degrees. I have never baught one for my stock bike, but it would help some, because higher octang fuel will acually burn slower than pump gas, retarding your timing, and thats why its good to advance it.

 

thanks guys any suggestions is appreciated

 

I would try the thinner head gasket. You might try seperating the stock head gasket and running just one of the three layers, with sealer of course. The 38 mm A/S carb is easily the best 38 mm for open riding, the TMX might be a little better for woods, but I have no complaints with the airstryker. The stocker 34 belongs in the backup parts bin... I would also either get a Boyeson Rad Valve or V-Force reeds. The bumped compression, larger carb, CR intake and reeds will really wake up a 250cc motor. I also don't recommend adding octane booster. If you have to, mix it with the gas only and consider the amount mixed in when adding oil. If you add booster to a 40:1 mix it can easily become 38 or 39:1 and really screw with your jetting... Keep in mind that bumping the compression may not make you faster. The extra compression will add bottom end snap, but may slow down actual top-end speed. I know of several 250-330 engines running lower compression to reduce wheelspin and increase trap speed.

 

EXACTLY what nicname says depending on where you ride. i run an oring head where i can ajust my compession ratio. small dome on a short race track and big dome in the sand dunes.