265 Big Bore Reviews?

[MXR]

I’m looking at getting a 265 big bore for technical trail riding. I like my 03RM 250’s motor, but still want more power especially on the bottom through the midrange without losing a lot of my topend. I don’t like a 300 feeling topend. I feel the 300’s go flat. Anybody have any experience, feedback on the power characteristics of their 265’s??

[highmarker]

what motor?

[MXR]

what motor?

03 RM250

[1.21GW]

If I remember correctly there is a massive thread in Yahama 2 stroke forum on this topic and lots of discussion around the various tuning options to change the power curve.

[OldMechanik]

Tom Morgan of Factory Kawasaki had this to say:

The most economical change that also performers very well is an over-bore to 265cc. This engine gains power and torque at all RPM, especially at part throttle opening and mid range. You would need to send me the cylinder assembly and head. The work perfrormed would be:

    a) Bore cylinder and NSC plate to 265cc

    b) Modify Exhaust valve to clear larger bore

    c) Complete porting work for your type of use and the big bore

    d) Head modification for big bore, your altitude, and the fuel that you prefer to use (pump gas most likely)

    e) oversize piston kit

    f) Complete dissassembly, cleaning and reassembly of the cylinder.

-OR-

The 295cc big bore is the next step. It receives the same modifications as the 265, just bigger bore and it comes with a head gasket. These engines gain considerable power at all RPM but tend to be more of a bottom-mid type of power. The top end power can be increased substantially if I do modifications to the crankcases which would require a bottom end engine rebuild also.

[MXR]

Tom Morgan of Factory Kawasaki had this to say:
The most economical change that also performers very well is an over-bore to 265cc. This engine gains power and torque at all RPM, especially at part throttle opening and mid range. You would need to send me the cylinder assembly and head. The work perfrormed would be:
    a) Bore cylinder and NSC plate to 265cc
     Modify Exhaust valve to clear larger bore
    c) Complete porting work for your type of use and the big bore
    d) Head modification for big bore, your altitude, and the fuel that you prefer to use (pump gas most likely)
    e) oversize piston kit
    f) Complete dissassembly, cleaning and reassembly of the cylinder.
-OR-
The 295cc big bore is the next step. It receives the same modifications as the 265, just bigger bore and it comes with a head gasket. These engines gain considerable power at all RPM but tend to be more of a bottom-mid type of power. The top end power can be increased substantially if I do modifications to the crankcases which would require a bottom end engine rebuild also.

Thanks for the feedback. I’m wanting to just get a little more power especially low and mid, without losing too much topend. I really like 250’s more than 300’s for that reason. I know Tom Morgan is highly respected. You’ve given me some great food for thought. Thanks again.

[MXR]

Update... I just found on Craigslist an 03 RM250 that just got a couple months back the millennium technologies big bore treatment with $1300 worth of new parts with the the receipts to prove it. I got it for $1800 which I think is a steal considering everything was new or rebuilt except the linkage bearings. (New pro circuit pipe, chain, sprockets, brake pads, reeds, tires, tubes, seat cover, wheel bearings, and the list goes on and on). I can testify it’s my favorite two stroke motor I’ve ever ridden and I’ve had a good sampling of bikes. I’ve had 14 different bikes from 125’s, kdx 200,220, a bunch of 250’s, a gasgas300, and a cr500. The only thing I haven’t ridden are the new KTM’s, GasGas, or Betas. I’m afraid I’ll want one, so I avoid them. Lol

The RM265 has more bottom end grunt and midrange than my Eric Gorr built 250 (which I love). It feels almost right in between the power of a 250 vs a 300 but stills has an awesome topend. My friend who used to race super cross in the late 70’s and early 80’s and has had dozens of bikes, said it’s the best motor he’s ever felt. It barks and is strong without having any weird powerband hit, and it revs to the moon.

Millennium bored it to 265, ported and polished it, did some powervalve magic, and I’m assuming the squish band as well. According to the receipt it was just under $600. Anyway. I highly suggest the 265 package. I’m sure Eric Gorr’s would be comparable. They’re amazing. I now have to sell my 14 RMZ450, because although my wife is cool, she won’t understand having three bikes. Lol

 

[OldMechanik]

Awesome deal! I would like to see a video and/or some pics!

[MXR]

Awesome deal! I would like to see a video and/or some pics!

Thanks. I felt like it was a really good deal too. I have some nice cycra handguards, protaper windham bend bars, and bar risers off my RMZ450, plus some other goodies to put on it to set it up like my other RM250. I want them to have the same feel etc. I’m just going to buy a $25 tusk pipe guard, repack the silencer and put a good skid plate on it. ALL IN $2000. Not bad.

[zig06]

That was a steal!!, nice bike!

Had Millennium turn my '99 RM250 into a 295, the power change was VERY dramatic!  It did lose that 250 quick rev, but the power increase was amazing, I highly recommend Millennium based on what they did for me.  I did have to go 2 sizes smaller on the main and pilot, but stayed with the needle at the 2nd clip position (2nd down).  The port work and head work was top notch and (looked very professional). 

With the '96 through 2000 RM250's you do have to split the cases and grind down a small boss on the front of the crankcase otherwise the piston skirt will hit it (found out the hard way), as a 265 you should be safe.  Also, I did not need to convert over to a head gasket, that model was still able to retain the stock dual o-ring head seal.

Personally I'd like to try to find a '04 or newer RM250 and make it a 265, with a Gnarly pipe and Millenniums custom porting - mine was similar to what they use in their "TMR Engines", pretty much a "more power everywhere" kind of porting.  Which is really what everyone wants if your looking for more low end but do not want to lose any of the top end pull.

[MXR]

Thanks for the feedback. I wish I could ride your 295 to see what it feels like. Sounds awesome. I agree with you on the Gnarly. But, can tell you that the Pro Circuit Pipe feels really good too. The 265 feels so much more grunty in the bottom and mid than my already modified 250, but it feels like it almost has the same top end as the 250 does. I’m assuming the porting on the 265 is the broad everywhere porting, because it feels like it. The Gnarly in my opinion would probably give it even more grunt without suffering too much top end loss. If I munch my pipe I’m going to get that one next for either one of my bikes.