YZ 125 Big Bore Help Needed

[Nillian]

Hello everyone, I stumbled into this forum while searching for big bore information. I am seriously considering doing a 139 and I'm not sure where to go, any help would be great!

I have an '02 and will probably want to stick with 93 octance.

I was looking at RPM but it seems to me that with his price increases over the last few years you are paying for the name and the magazine reviews... I've heard great things about the kits but I'm still not jumping up and down to drop $800!

I read some info on Eric Gorr, and I'm very curious to know how his 139 stacks up to RPM's. I also saw Eric does a 144 but I've heard that the larger piston takes away from overrev (anyone know if that's true).

Any personal experience the readers of this forum could share with me would be greatly appreciated. Any other companies, good stuff, bad stuff, any info at all!

Thanks alot!

[OLDMXRACER 393]

BUMP! Welcome to ATM Nillian. You'll have an opinion soon I'm sure.

[madcow393]

look up Fast Forward Racing. One of the members on here is part of them. FFRacing11x(gues where the FFRacing is from) he replated my cylinder and head. they came out great. and if you get Eric Gorr's book about working on bikes. FFRacing's hands are in some of the shots.

[Dirtrydar]

just put a maico 490 in it and ull have no worries

[MotoMan]

A word to the wise.

Stay away from RPM. I had a run in with Rick and a 285cc kit for my 99 yz250. Let's just say some of his business practices leave a little to be desired for my tastes.

If it where me I would go with Eric Gorr. I have heard nothing but good things about Mr. Gorr.

BTW, welcome to ATM!!

[Nillian]

I appreciate the comments. I'm leaning towards Eric Gorr. I used to race 250B and after a couple bad hospital visits I stayed away for whle. The bike I'm trying to build is just a more powerful 125 until I heal up a bit more and start racing again.

What I am really looking for here testimonials from actual 125 big bore owners... Should I go with a 139 or a 144. What are the characteristics of each?

Thanks again!

[Dell30rb]

If you really want to build a race machine, start by getting your suspension setup and revalved for you. These days, the stock motors on all of the big 5 bikes are plenty strong for anyone up to a B or A rider.

In racing, suspension comes first. Bigger power does help however, but if it were my personal bike I wouldnt touch the motor until the suspension worked flawlessly!

Just my 2 cents.

However, I will still answer your question (or at least try too). I have heard some terrible stuff about RPM's kits. I wouldnt buy one. I have also heard some bad stuff about eric gorr. One of my buddies was getting a 133 bore and plate, however eric accdientally had his cylinder bored to 144. The particurlar bike needed bottom end work to run a 144 bore, and eric said he would do it for free, but my buddy wanted a 133. So eric had another customer who wanted a 144 with the same bike (but 1 year newer) and he swapped their cylinders and all was good. He fixed his mistake, however it took 2 months . Also, some fella at DRN got totally screwed by gorr. He seized an old RMX and the powervalve was completely screwed up. Eric said he would replate and bore the cylinder oversize, and fix the powervalve. However the cylinder came back with the same screwed up powervalve, and with the wrong cylinder studs. Eric let him send it back, but he had to pay shipping and it took an extra month.

These are just stories i've heard. I am not offering my opinion on gorr's work. Just repeating what i've heard.

[ossagp]

I will try to answer the question you actually asked rather than do something akin to philisophy:

I currently own a 139 kitted yz done by Rick Peterson. It works super well. I have owned it for three years. I have nothing but good to say about him, and he has always been available to chat with, not that I needed anymore help on the YZ than the work mentioned.

My son had a CR125 done by Eric Gorr. Same story. The machine worked flawlessly as a 144. In all it was used by my son and nephew for 4 seasons. My nephew didnt have as good a luck with it, but actually has had more difficulty with a 2003 KX this year than he did in two years with the "old CR".

The yz is set to run 50/50 race/pump gas. It is noticeably better in acceleration and low end compared to the CR. It was also about twice the money to do the yz. Both have had numerous piston changes and are on the same plating. The Honda from Gorr likely has 3 times as much time on it, and by now could use replating. Way better than what Honda sent though.

If you want to run the 144 kit on the yamaha you will have to mill or grind away the front of the case where the cylinder extends into the case. The piston skirt will hit it otherwise. The 139 should clear, but check, as a casting flaw had to be filed off of mine before it would clear.

Email me if you want more, as I was not on this forum to answer sooner. [Only registered and activated users can see links. ]

[Faded]

I've worked with Eric Gorr on my current bike. I can say that the work was top notch and I plan on sending him the parts off of my future bikes down the road. After I got my junk back I refered five other people in my area that sent in thier cylinders. Eric Gorr's experience speaks volumes, they guy has hand ported well over 40,000 cylinders by now. He is the only one that does the work, not some monkey with a set of files being told what and what not to do. He will even tell you what he's going to do if you ask, it's not some 'secret' like a bunch of the other companies. The guy is only human though and will make mistakes. If you'll notice even in Dell's stories the guy is more than happy to do what it takes to make things right. He offers a satisfaction guarantee, if you're not happy he'll do what it takes.

Don't worry about the 144 lacking in over-rev, it's all in the porting. Be aware that if you do choose to have it ported for more mid to top ring life is comprimised and requires more frequent changes. Good luck, let us know what route you choose and what becomes of it.

[Keith 455]

If you are serious about a big bore, their is only one man I would trust with my motor besides me. Wes Gilbert from boyesen precision porting . He has an extensive engineering background that goes along with his excellent work!!!!! Here is the number you can thank me later. 1888-269-3736

[Nillian]

Hey everyone, thanks for your comments. (And don't worry about my suspension, it was setup a while before I posted).

Now that the snow is on the ground I've decided to send my motor to Eric Gorr for a 144 kit. My decision was largely decided by price, but Eric is also located closer to me then the other shops mentioned and has been courteous on the phone as well.

In doing some research through older magazines I was humored by the incredible price increases RPM has had from just a few years ago... and since I will probably buy a 4 stroke next year I just can't justify paying $900 something for a 139, even though I like the idea of an extra ring in the piston...

Again, thanks for the comments and I'll let you all know how well it runs!

[atreyu]

gorr is the man. RPM has too many rider complaints for my taste.

[Faded]

Nillian,

I thought you were dead...

Congrats on the decision, sounds like you'll be having some fun in the upcoming year. What porting specs and fuel requirements did you choose? Just curious... Good luck!

[MotoMan]

Can't go wrong with Gorr.

[FFRacing11x]

For what it is worth...I have worked elbow to elbow with Eric...he has taught me loads of what I claim to know. he stands behind his work as mishaps do occassionally occur. Eric is THE MAN!! Wes at Boyesen is also top notch...but I know for a fact that both rick and Wes have sent jobs to eric that they could not handle. Besides, eric sponsors this site, and should be supported.

[ossagp]

If you told Eric Gorr you wanted the two ring piston he would probably do that too. I have some, in 57mm from RPM and he would sell a piston to anyone. The 57 is easier to install on your bike because the case will not have to be modified to clear the skirt in most cases. Mine actually required it on the 57 even. Not hard,,but splitting the cases is really the best way if it is needed. You can also align the insanely off rear boost port too.

I like my 139, but for the price difference Gorr is the place to go. I am about to send him another cr250 cylinder (2001).