Anyone ever work a 250X engine

[DTRAIN]

Well my 88 250x has seen better days. It is currently in the shop ready to be torn apart. I am hoping that the problem is in the top end, but if it isn't, that means an overhaul of sorts for me. If I have to break into the bottom end I would like to add a high compression piston and and possibly bore out the sleeve to .040 or .060. If I do this must I change the cam, and or harden the rockers? As always money is a factor. I would like to make some power gains but nothing that is going to empty out the bank account. Anyone out there ever work over a 250x engine. What should I go with and what knid of power gains would I receive? Thanks ahead of time.

[badass400ex]

you dont need to get into the bottom end for the piston thats part of the top end i had a 12-1 in my old 250x and it would get hot in the woods and start pinging on 94 octane gas i would reccament getting a full exhaust that woulg be the biggest thing you could do but to put the piston in you do not have to hardin anything the cam would help alot and would take advantage of the high compression i think that had a big part om mine overheating it had a stock cam!

[DTRAIN]

What kind of power gains did you get from the high compression piston as compared to the stock piston? Also , how would boring out the sleeve affect how hot the engine runs?

[Scott]

Bumping the compression ratio up makes it run hotter. If you stay at 11:1 or lower, you should be able to run on high octane pump gas. Check out the Q&A session with Mickey Dunlap on the EX Tech page of this site, he talks in one of the posts about the 250X/300EX head and how large gains can be made in the performance by a port/polish and larger valves. He also discusses how the compression ratio you think you're getting can be higher than what you actually have.

I have a K&N and a pipe on a 300EX, with the jet bumped to 125. If you haven't done the filter and pipe to your 250X yet, that would be one place to start. If it needs bored, you have no choice, you have to rebuild it. I would go only as large as needed to remove any scratches and make the cylinder round again(if it's egg-shaped from wear). That leaves as much metal as possible in the cylinder walls and allows for additional rebuilds without replacing the jug.

I would check and see what the price of port/polish, valves/springs are compared to cam/hardened rockers. With money an issue, I'd go with whichever is cheaper.

Good Luck.

[DTRAIN]

I have thought about getting a pipe and jet kit but I cannot have a loud quad. My buddy has a warrior with a pipe on it and it sounds like a train coming through the woods. On more than one occassion it has gotten him caught for being somewhere where he is not supposed to be. Will porting and polishing still increase performance with a stock pipe, air filter, and jets? Also if I port and polish will I have to re-jet to get the right mixture of air and fuel? Or am I just confused as to what porting actually is? Thanks... Eric

[Scott]

I understand about the noise. To try to let it flow better, you HAVE to change the head pipe at least. Until last week, my 300 was running a modified DG headpipe into the factory muffler with the baffle removed. The factory muffler is still restrictive enough that you don't need to re-jet, so you're not getting massive gains, but it was a little better than stock. I think someone posted that FST has a headpipe that fits into the stock mufler so you can stay quiet. That might be easier than modifying an existing headpipe. 1.5" pipe from the cylinder back is what the 250/300 aftermarket pipes are.

Forget the port/polish/valves/springs if you're not changing the muffler. It would be a waste of money. Get a K&N or Uni filter and a larger headpipe. If you keep that factory muffler on the bike, you shouldn't need to re-jet, even if you take the baffle out. Just having a fresh rebuild will give you better power and response compared to how it ran before you took it in the shop.

[TRX250XFIRE]

i have a 88 250x and i love it, it is ported and polished, and bored 80 over,i also have a DG pipe on it. it is not jetted nor do i have a KN air filter, im getting one this friday though. i have found that my 250x runs better in the cold? i do not know y though. i have noticed major power gains from the boring and the pipe. does anyone have a gess as to y it runs better in the cold???
thanks

[Scott]

put a better flowing air filter on it and richen up the carb so you take advantage of the bore and port/polish job and you'll probably be very surprised how much power you had but were not using.

[DTRAIN]

Did you port/polish/bore and pipe at the same time or did you do it separatly? If separately than how much of a power gain did you get from each? Also, when you bored over.080 did you get a high compreession piston? If so than did you have to mix pump gas and race gas, or pump gas worked just fine. Also did you replace the cam when you had the engine bored?

[TRX250XFIRE]

after i got done wrighting my first post in this topic i was thinking about the air filter. i think that is a pretty good idea. As to weather or not i ported polished piped and bored it at the same time. yes. i bought it about 3 years ago, from a older friend that had alot of money and alot of free time. while he had it the motor was blown. he took the motor to some place in Syrucuse. He tells me that they ported and polished it. and bored it 80 over. after he got it back and put everything back togeather a friend of his had a dg pipe for sale so he bought that off him. as to weather they changed the cam or not i do not know. but i would belive that they would of because it was blown up and they might of went through the hole thing, but im not for certin. he told me that after everything was accomplished there was a major power gain in every thing. i run the high test gas that u get at a gas station but i do not buy any of that serious race gas. i do think that it runs a bit better with the higher octain then the lower. i think that it is pretty fast, i can pretty much beat any stock 300 in a drag race unless i screw up or something. at a local fair they had a drag racing event and i beat 2 300's and a warrior. but then lost to anouther warrior in the finals and took 2nd. but i dont know, it was probly just luck...

[R-Crazy]

a sprocket is also a nice cheap investment. i raised it a tooth. it gave me okay power gains for 20 bucks.

dave