Service Honda Yamaha YZ300

I noticed this post by AJ from Service Honda on the CR500 riders forum, it looks like he is building a 2009 YZ300....should be a nice bike...

"I'm doing an open class YZ, but it is a 300 (bored out 09 YZ250)"

"yes it will be availible, and i will post some photos when i get some !

(but as it is simply engine work, it will look exactly like a 09 YZ250 but with service yamaha graphics)

as far as time frame, i'm waiting on particular items for it,

some to be manufactuered still, so it may be a month or two..

My best guess is i wil hacve i tdone soon, and test a bit,,

and plan for a january or febuary release, of the model..


service honda bought out a multiline dealership in their area so now they are able to work on kawis, yams and suzukis as well as hondas.

there was talk of a RMZ250 alum frame with an late model RM250 motor in.

ive been biting my tongue on the rm/yz295 for a while.

Interesting. I wonder what frame he's putting it in???

The perimeter frame idea never made good sense on a two stroke. The Yamaha 4 stroke frame is not a perimeter design, its just made to look like one. Notice how the frame connects to a single backbone as it goes under the tank. Other than the angle of the side members, its basically the same frame as the 2005 yz 250...

I just dont see any gain in dropping the yz 250 engine into the 4t frame. The new tank and shrouds is bound to look better (hell, anything would), but as far as a handling gain...There may be a handling loss.

read it again-they arent doing a frame swap on the YZs, just a regular YZ250 with an irregular cylinder.

Oh crap....being associated with service honda, I hoped for a frame swap. I saw a service Honda once and it was beautiful. Really, I suppose the cool part was how normal it looked. The sticker was the only giveaway that work had been done. The s/h frame pieces were far nicer than stock. The highlight of this post is the 300cc's. that I would upgrade to now. I find my bike lacking in power for my ability.....You know, ripping fast 43 year old with house and bills. Also a granddaughter that cries when she cannot ride with me....

They would have the technology to build a kit to accept modern plastic......That might be the best of both worlds.

The rmz machine sounds plenty fun, however.

He is also doing a kx300 into a kx250f frame.Keeping the 2 strokes alive!:thumbsup:

sounds like fun! Over-quadratic? yes yes! :moon:

Though it sounds great, I've read several times that the experts found the 285 to be the biggest displacement that will work well on the 250 motor. However, SH may have a stroker crank or hi-comp setup of some kind :thumbsup:

its just a 295 big bore, and i am sure it will run well.

there is a piston people have used on the old KX250s to make them a 310 and they ran well if done right.

Yes, the KX310 runs well. Mine has about the same topend as the stock 250 did... but the low to mid power is greatly improved!

Don't get me wrong- I'm sure it's lovely :moon:

I have no doubt it'll run well also... My point was just that you don't gain much power after you exceed 285cc based on what i've read several times... that is just according to pro tuners though :thumbsup:

I would have no trouble owning, hammering, and loving a 300yz... don't worry:applause:

I'll bet that peak HP is not improved after a certain point (you are limited by available port area/time) but low/mid power can be increased.

Agitator,its not a matter of it running well or how much power will be gained going larger than a 285,the fact is that from what Ive been told if you go larger than 285 you will run into over heating problems.You were correct in saying that it might be some type of stroker kit that service honda is going to use.Its going to be a stroker kit or a completely new cylinder such as an Athena or there own cylinder with a larger bore.

you guys crack me up!

If they did a new cylinder with 300 cc's in mind from the start, it will probably be great. I imagine there is somethign different about what they are doing or AJ woudl have never posted.

300 kit!! wow, now if they just get it perfected and sell us the kits for under 400.00 That would be sweet!!! ok maybe 450.00 with the gasket kit:thumbsup:

The trouble with boring too much is you get too over square and farther away from the "magical" bore /stroke combination that every manufacturer has found perfect in the 250cc class.

Maybe the 285 bore with a bit of stroking wound be the go:thumbsup:

The trouble with boring too much is you get too over square and farther away from the "majical" bore /stroke combination that every manufacturer has found perfect in the 250cc class.

Maybe the 285 bore with a bit of stroking wound be the go:thumbsup:

I agree with BeRM.. The "magical ratio" is very important to the 2t design.. Slightly longer stroke with a 285 would be :thumbsup: I bet

what happen to the old spacer plate style stroker kits??? Like honda use to have the 5mm plate then the piston with the 5mm off set?? Maybe they called it a long rod or something like that.

I know a guy that just bought a KX500AF from Sevice Honda he went with the KX over the CR because the KX motor has the power valve.

Here's a link with pics:

I'll wait for the WR300 two stroke please

The trouble with boring too much is you get too over square and farther away from the "magical" bore /stroke combination that every manufacturer has found perfect in the 250cc class.

Maybe the 285 bore with a bit of stroking wound be the go:thumbsup:

I agree with you and bikedude

There's a magic balance for the motor. Once you go over-quadratic (more bore than stroke) by a large amount, the engine will build revs faster and have a more erratic power band no matter how you port it. Of course, building a new stroker crank may make bore and stroke pretty close again. If you combine that with "making" a new cylinder that is ported for the size and also has adequate cooling passages... hey- a machinist can do anything.

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