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40 hp 250...

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In the first place, that's 39 horsepower, not 40. In the second, a stone stock '04 produced 36. (See Chart) Big Gun, the pipe people, has come up with port modifications that chart out at 40 with just the porting and a pipe...stock cams, compression, and everything. It's quite believeable, yes.

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sheesh Gray...I mostly thought it was interesting...not unbelieveable and the stock bike started out with lots less than 36

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40 horse isnt that great i hope to get 45 out of mine. Yosh TR 290 big bore and cams. Then maybe head work. I know a guy who is getting 48 horse it feels faster than a cr 250

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40 horse isnt that great i hope to get 45 out of mine. Yosh TR 290 big bore and cams. Then maybe head work. I know a guy who is getting 48 horse it feels faster than a cr 250

A 40 horsepower 250F is more than you think. Good luck getting 45.

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sheesh Gray...I mostly thought it was interesting...not unbelieveable and the stock bike started out with lots less than 36
Yamaha hasn't altered the engine in any significant way since it came out, especially not in the last 2 years ending in '05. I don't see why a stock 250F would ever have much less than the 36 that the FMF tuners got out of this one when prepping it for the shootout this chart was taken from.

What very often happens when an engine or equipment builder takes a baseline reading on a project for his "before" numbers is that the reading that results is of the bike just as it is, with an engine that is often far from optimized. Unless the bike is jetted and tuned to run as well as it can in stock form, a builder has no idea how much he really added to the bike with whatever modifications were made. Such comparisons are out of context, and not really very useful.

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Whats the stock horses on an '05? And how much could i get out of it

36.

How much do you want to get out of it? 315cc is maxed bore and stroke.

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you may jump all over that, and ur dealer will jump all over ur wallet. Truely how reliable would a 315cc bore comin from a 249cc?? That a big jump!!

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I came across this thread rather by accident, but I thought I'd jump in and answer a few questions. 40hp? Almost. Haven't had a true 250 make 40 yet but I've had them in the 39-39.5 range. As for a stocker making 36hp, not on my dyno they don't. Pre-'06 make around 32hp on pump gas, that's with the proper jetting. (leaned out a bit) Add 1 hp for 2006 models from what I've seen, the head is slightly better. So as someone said, that's around +7hp over stock, which is the correct way of interpreting dyno charts. I don't get into "numbers wars" I prefer to look at the delta instead. Squeezing 7hp more out of a YZ250F isn't all that easy, it takes a certain combination of parts and a lot of tuning to make it all work as intended. There is a lot of hype out there, so you have to take everything with a grain of salt that you read.

Reliability: Pretty good. In expert hands they will run a full season, but it takes a mid-season cam chain swap, rings, and new valve springs. I have had a smidgen of trouble with camshaft journal wear on the exhaust side but I should have billet cams available sometime soon to rectify that. You have to watch the valves closely. (I use OEM) After 1 season it is time for a total rebuild from the crank up.

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What cams are you using on the 06 262?

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45 is possible, but unlikely for an average person, you iwll be sending the motor out to someone big and they will most likely have to go completely threw the motor to get the best of everything

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id say it is feesable.. i dont know if or how much better the kxf 250 is than the yami motor but grant langstons ama legal 250f pumps out 44 hp....

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Man does anybody make a 315 kit because i would jump all over that!

Rick Peterson designed it. It's a bore and stroke job, not just a bore...ATAZ.

Very reliable from what I've heard. Rick is the man. He is also a member of TT, so ask him all the techno questions you want...he'll be more than glad to answer them for you.

Http://www.maxpower-engines.com

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id say it is feesable.. i dont know if or how much better the kxf 250 is than the yami motor but grant langstons ama legal 250f pumps out 44 hp....

What? 44hp?

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