Eric Gorr YZ144 -- 2 Strokes ain't dead!

For all of you that think the 2 stroke can't be competitive in modern MX..........

My 19 year old son has been racing for the past 6 years. he started out on 80's, moved to a 125, then like everyone else, a 250F. At 15, the awful parent that I am, turned all of his racing expenses over to him. He paid for bikes, maintenance, practice and race fees. I got him to the track and back, but he handled the rest. (I did provide the lawn mowers for his grass cutting business just so you won't think too bad of me). He bought the 250F in August of '03 right before the '04's were released. He bought a Yamaha and for the most part, it held up to it's reputation as being reliable. He broke 4th gear twice in the 2 1/2 years he owned it, replaced the valves w/ Kibblewhite stainless, plus three top ends --$2400 to $2600 in engine maintenance.

January of this year, he decided it was time to return to the 2 stroke. Weary of $1k a year maintenance and trouble getting it re-lit in the heat of battle, he bought an '05 YZ125. Stock, it's a great 125. But in the world of 4 strokes, a less capable rider can turn faster laps. One slight lapse of concentration and the guy behind you is now in front. He was just about ready to go buy a 450 (forget skill, gimme horsepower!) I convinced him to look at the 144 big bore. For what it would cost by the time he sold the 125 and bought the 4 stroke, he would be out $1500. The big bore was $500. $1000 will buy a lot of stuff.

I pulled the motor and sent it to Eric. Ten days later, I had it back. UPS got a little rambunctious in shipping, so we had to order a couple of parts.

I finally got the motor put back in this past weekend. I rode it around the yard and thought the power was noticeably better right off of idle. But the back yard and track are in no way alike. Friday after Thanksgiving we went to the track and - Wow! What a difference! The acceleration out of turns is unbelievable. My son was able to clear a 70' triple out of a turn from the inside with no problem. He tried a few second gear starts and had to work to keep the front wheel on the ground. And I haven't even touched the jetting yet. It's a little fat in the middle, so I'm going to drop the needle. It can only get better! We're also going to go back to stock gearing (currently one up on the rear) so he can hold third a little longer. We lost some over-rev, but that was expected. The next gear will pull with no problem anyway. This thing pulled my 190lbs. around like a 250F. You don't fan the clutch, just flick it. I can't ride 125's worth a flip, but I could ride this one! It was much more than I ever imagined it would be. We went with mid to top porting, but this thing still pulls from the basement. No more excuses!!!

Excellent Work! If you have a 125, this is the best $500.00 you could ever spend. Thank You Eric!

Maybe I go mid to top since I dont want to loose much top end , as you have said you have better off idle power and response.I figured it out that your midrange power is incredible with longer over rev.By the way was it set up to run on pump or race gas?

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If you want to maintain the top end, go with mid to top porting. The overbore gives you more bottom. However, it did lose some over-rev. The bore to stroke ratio is higher than the stock motor so the extreme upper end of the rev range is affected (I'm guessing that's why Eric stroked his). But the pull of the motor is so strong, it is very obvious when you should shift - and when you do, it just starts pulling again.

We decided to stay with pump gas -- Eric said we could see even more gains had we chosen to go race gas, but we did not want to be stuck having to run race gas. If we were attempting to hit all of the big nationals with it, we might have thought differently. But we play as much as we race these days.

Eric's contact info - ericgorr@hotmail.com

The question concerning the "stock" class is a good one. The rule states that the bike must start as a 125 and the increase in displacement can only be achieved by boring -- no stroking allowed. So, it really isn't stock anymore, but the only bike that comes stock as a 144, the KTM 144SX is not legal in this class because it didn't start life as a 125. If it were me, I'd make a call to MX Sports and get them to clarify it for you -- and send you a letter so you will have in writing what they told you.

My carb is the same. It seems a little rich in the middle but I think I can fix that with just the needle.

We are running a a PC pipe w/ shorty silencer and a V-Force 3. It seems to have really good snap off the bottom even though it's ported for mid to top. It would probably have more over-rev if we went with the standard length silencer. That snap off of the bottom really gives it a strong pull out of the turns though.

The 144 will not pull as long as the 250F. In third gear roll-on's, a 250F is virtually equal with a 250T. But the 144 makes it a much more level playing field. If a 250F rider complains about competing with a 144, he ought to go practice more.....

We only have about 3 hours on our YZ144, so I don't know yet. I think Eric recommends rings @ 15hrs.

The current jetting is exactly the same as it was when we bought the bike. However, I don't know if it's stock or not. We bought used and the bike had a PC pipe and silencer and a V-Force 3. We are at sea level and the bike was perfect when we got it. After Eric did the 144 conversion, it seems a little rich in the middle, but probably just 1 clip position - not enough that I've even messed with it yet. When I pull it apart to move the clip, I'll check what's installed and post here - maybe before the weekend?!

Okay, here is my jetting ---

40 Pilot
420 Main
Needle 3rd Clip position (Was in the 4th)

The bike has a PC pipe, shorty silencer, V Force 3, and Power Now (air box side only). We ride roughly @ sea level and relatively high humidity. Bike is set up for pump gas. Hope this helps!