Gorr 05 YZ144 project is a success

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#1
Eric,

More detailed reports to come later, but in a nutshell my project bike is done and finally got to practice on an indoor mx track.

-Eric Gorr 144 engine with more better porting. Pipe/shorty silencer.

-187 lbs, all fluids, no gas. I dropped nearly 10 lbs on the lightest bike made. I'll add my findings on DRN later as you'll be surprised on the $ per lb. of every item.

-Quick throttle from Racer's Edge takes the range of the throttle and cuts it in half. I have a wrist injury preventing me from going full throttle.

Ride report: Wow. :) Crisp down low, huge midrange, and screaming top end. Thanks Eric for such a terrific motor. Doubling from the inside line out of a corner is made easy. If you've ever been to a supercross, this bike sounds like a works 125.

Next on the to do list: Pick up my Ult.2 gas, work on jetting and adv. timing and add a delta 3 valve.

Giving credit to where its due here on DRN, Steve125 and Marcusgunby thanks for all the modded 125 work you have done and 144 tidbits. Saved me a ton of time in dialing it in from the start. Rich, thanks for your fuel knowledge. Eric, your motor work rocks! I had 6 riders come up to me at practice and as who did my motor work. Thanks guys. :laugh:

Can't wait to take on 450's in the vet class next season.
 
- a d v e r t i s e m e n t -

marcusgunby

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#2
Im kindof tempted with a yz144 but i need to ge tthis 4 stroke thing out of my system first:(
 

Studboy

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#3
Pray that you get it out quickly Marcus!!! :) :) :)
 

steve125

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#4
147 Leeman,thats just awesome!!! :cool: I can't wait to do mine now!! Ive been all wrapped up in the RM/YZ 250's as of late, but the 05 YZ 144 is my next project.

Funny on the sound of these 144's, when tuned right, they do sound so works like. I always get the :cool: comments from other riders.

Did Eric do the mo-everywhere or mid to top porting? Race fuel spec?

Hey Eric, could you chime in here and give us some background on the new 05 YZ 125 to a 144. Was it pretty much straight forward???

Marcus this info must have you in a twist. ;)
 
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Eric Gorr

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#7
Hi guys,
Thanks for the good words on the 144. Overall I like the new YZ125 engine. That thing is built tighter than a KX65! The extremely short intake enabled Yamaha to keep a straight path to the crankcase. It looks like they are trying to reduce the crankcase volume and the transition from the cases to the transfers is excellent, theres no opportunities to improve the flow with porting, so if some ambitious tuning company tells you that the cases need to be split on a new bike in order to port them, they're just looking to score more of your hard earned money. The cylinder allows for greater overbores because of the increased thickness, but hanging a big heavy piston on the end of the rod is just going to slow this bike down. The stock porting and head design are the most conservative since the 1998 model YZ125. This is the porting that I used for Ben's bike; the exhaust port opens 27.5mm ATDC and the transfers are staggered for more top end with a starting opening of 41.5mm ATDC. That's shifter kart timing!

Are you guys at Max Power writing these specs down? Since you clowns seem to copy everything else I do including my web site, pricing, tech articles, services, and piston designs. You might as well steal this too!

The stock head design seems to be adopted to reduce squish velocity and eliminate the chronic YZ problem of cylinder and head errosion due to o-ring leaks. I first saw this piston design 2 years ago when I bought out a batch of Yamaha of Troy's race team once they switched to YZFs.
I think that Yamaha should've used a shallow conical crown design like my 144 piston, and pinned the head to the cylinder and widened the exhaust bridge if they were really serious about making the engine more reliable.

The set-up for a cross-country ridden engine is much different than Ben's YZ. The port timing is more conservative than stock because when we bore a cylinder 4mm oversize the ports drop in the cylinder wall because of the roof angles. So that enables me to raise the ports to whatever timing works best for the application. Sometimes we'll Tig weld the exhaust bridge then stress relieve it to give the ring more support. Of course the exhaust port area is reduced but thats exactly what you need for an off-road engine that might peak at only 9,500 rpm.

If I had more resources I'd make special pipes for 144s, but generally speaking a pipe with a larger diameter center section like a FMF Fatty is a good choice. The SST pipe might make the engine run hot because of the constricted convergence cone to stinger transition. When that pipe started to become popular I changed the design of my piston to position 50% of the mass in the piston crown to reduce the chance of melting a hole in the center from use with an SST pipe.

For guys looking for even more displacement I'm stocking stroker cranks of 58.5mm for quick trade-ups. I'm working with TNR Machine in Dowling Michigan. They have the most precise method of locating the new pin holes on the crank. Unlike our competitors Max Power and RPM we don't need to weld the crank pin to the flyweights because TNR can hold precise tolerances on the new pin hole inside diameter and location. So our cranks can be rebuilt repeatedly using traditional technology, Welded cranks are pretty much set in stone. In order to rebuild them you have to mill-down the pin and flyweights past the weldment just to disassemble them.

As far as the stock YZ125 is concerned, my current set-up for expert riders is to reconfigure the head for a flat top Wiseco piston (762MO5400) then raise the exhaust port and stagger the transfers. So far people are pretty happy with that set-up.

Overall I think Yamaha has done a great job at investing in the 125 2-stroke class with a lightweight chassis. With the AMA banning 4-strokes from the schoolboy class and considering a separate 2 & 4 stroke class for the future, the 05YZ125 should be the bike of the class. I'm expecting the American aftermarket to step up to the plate and produce titanium bolt and axle kits for this bike to make it even lighter.

Eric
 

Studboy

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#8
Good stuff Eric! Keep up the good work! I really enjoy reading your posts, it is great that we can correspond with one of the greatest tuners out there.
 
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#9
While we're on the subject of the 144, has anybody had and tried Eric's 133 of the 05 YZ125 yet? I sent my cylinder over to him the other day, just curious how people have found it, can't wait to get it back :).
Eric - You probably don't want to give the competition any more help, but are you using similar specs for the 133 as the 144?

Thanks
 
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#10
I see on your site that ring replacement should be every 5 hours with the 144 kit. Why such a short service interval?
 
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DEX

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#11
On the stock 2005 YZ 125 for Junior/Intermeadiate MX, what do you reccomend? I dont want a big bore kit and would like to stay on pump gas if possible. (Actually I have a whole barrel of Sunoco Supreme 114 octane left over so I was thinking of mixing it with Supreme pump gas a 90PG:10RG ratio. Even if it is still stock just to play it safe with detonation)
 

jake949

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#12
any chance of a update, the whole project. how you took the weight off your bike and the costs? how is the motor treating you. would you run it against a 250f?

eric what is the biggest you can go with the new yz125? stroker cranks?

i am a practice rider, just wanting a really fun bike.
 
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#13
Sorry for the delay on the updates,

The motor is still more than I expected. I've advanced the timing 1.5mm. Jetting stayed the same as it was a tad rich but now I'm running Ultimate2 oxy. gas and it cleaned up. Eric did make this engine to run on pump gas. FMF Factory Fatty exhaust is used and a shorty silencer. Delta III valve hasn't came in yet, that's my last engine mod. as it's about perfect right now.

As for if it will run against the 250f's, I've only been indoors on a tight SX track, so outdoors will be the true test.

Here are some findings when I went to make this thing light.


Removed rr. brake disc guard - 2 bolts, rr. caliper guard - 2 bolts, cut tabs to the corresponding bolts off, countershaft plastic guard and replaced metal guard with shorter bolts, cut carb. drain tubes to be flush with linkage on stand, removed lower fr. brake line holder steel piece and replaced w/ zip tie (not the piece on the fork guard but the 2nd lower guide), removed tank strap, cut backside of airbox to be flush with the rear fender (causes turbulence of the air entering from the rear so I've read), removed the rubber cover off of throttle assembly.
Total of 16 ounces removed.

In no particular order:
Michelin M12 front tire + Michelin S12 rear tire -41 ounces
Cryo Aluminum clutch plates -8 ounces
FMF Factory Fatty -2 ounces (all aftermarket others were more weight)
FMF shorty silencer - 14 ounces
EK MRDL chain -4 ounces
Factory Connection alum. shock preload rings -2 ounces
RCS titanium shock spring - 10 ounces !!! I heard 2-3 lbs.???
GYTR titanium subframe on ****- 13 ounces
4 Ride Engineering Alum. Banjo Bolts - 2 ounces
Renthal ultralight fr. sprocket (the one w/ drilled holes) - 1 ounce
Renthal ultralight rr. sprocket 46 tooth (stock was 48 but the motor flew through the stock gearing) - 2 ounces
Tusk gas vent valve with shortest connecting tube to the gas cap as possible - 2 ounces over stock length tubing
04 Honda CRF450 Aluminum front brake line clamp assembly (two pieces) + 04 Honda CRF450 Alum. front axle nut - 3 ounces
Hammerhead designs alum. shift lever tip - 1 ounce
Made my own alum. brake lever tip - 1 ounce
Made my own alum. spacer (huge steel spacer is stock) inside of upper chain roller - 1 ounce
Lightspeed C/F chain guide - 2 ounces
Lightspeed C/F fork guards - 2 ounces
Racebolts titanium swingarm bolt - 6 ounces
Mettec titanium fr. + rr. axles - 12 ounces
Lockhart Phillips alum. bolt kit for misc. plastic bodywork steel bolts - 4 ounces (14 bolts used total)
GYTR titanium rear sprocket bolts/nuts - 2 ounces
GYTR alum. drain bolt - 2 ounces

Total lost off the bike 9.5 lbs.

The surprises of no weight loss:
Cycralite FFender + 1 ounce (may be less for other models though, color didn't quite match the yamaha blue)
MotoMaster front disc was supposedly 40% lighter but with the relocating bracket came out to be + 1 ounce
SDG seat was exactly the same weight (this seat is lighter for CRF450's though)

Some additional weight lost off of riding gear:
Tech 4 boots -8 ounces from Tech6 (- 18 ounces from Tech 8)
M2R Rev. X Helmet 2lbs. 13 ounces - 8 ounces from most others like VFXR, Thor SVR, HJC models
Thor Phase jersey/pants/gloves - 8 ounces over Thor Core5 combo
Under Roost Deflector - 10 ounces over outer chest protector
 
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#14
Important note-

This project bike was made to be a project...that's all. The weight loss doesn't mean to go out and scrap all of your disc guards because you'll end up with bent rotors sooner than you think, and it doesn't mean throw your chest protector away or pick a helmet because of it's light weight over protection capabilities. I have my own practice track and will test these findings out on it only as this bike is illegal in the 125 class for weight reasons and it's a 144 now.

Figured this post would help some of the big 4strokes to shed some weight in areas to which you choose, not to make bikes go below the legal weight limits. :yeehaw:
 

steve125

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#15
Sounds like that bike flys, all you need are wings :)

Pete just sent my 144 cylinder out for plating, with port timing specs real close to yours. We will be running more compression and both the piston and head will be ceramic coated by Swain Tech.

How much do you weigh? I agree the std. gearing is right on for the stock bike, so 2 down in the rear sounds real close for the 144 kit.

I will be running the VP U-2 also and a timing advance along with a leaner main jet setting.

When weather and time allows I'll tune it in on the track and dyno. I will then post the final specs.
 
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