Improving my YZ125-HELP, PLEASE...

[Sam Simons]

I recently purchased a very nice '04 YZ 125,and IF I can modify it to produce more torque at lower RPM's for my trail riding,I'll keep it instead of having to opt for one of the gut-less 4 strokers(TTR 125,etc).
Presently,the bike has the FMF pipe & silencer,V Force reed ass'y,and 4 more teeth on the rear sprocket;it needs more help,possibly with a Stealthy flywheel weight and one of the
big bore conversions as a last resort. Altering the P-valve springs has been suggested-how?
So,I want to hear from any other YZ125 owners that have tried the flywheel weight and / or the big bore conversion.
Also,which big bore did they use and where to obtain it.

Finally-seat height- too high for my tastes- are there commercially made spacer kits available for both the rear shock and forks?

Thanks in advance,

Sam in Indiana

 

[robwbright]

You're never going to get serious low end out of a small bore.

My 144 was a very significant improvement. It didn't really increase the low end in relation to the rest of the power - but the bike now has approximately 20% more power everywhere.

I have a Steahley Flywheel weight on the bike now - 11 oz. Didn't make a lot of difference, but it is noticable. I don't like it because it smoothed out the hit too much for my taste in MX - but that may be exactly what you need for woods.

Eric Gorr did the work - About $500 for the whole kit including piston, ring, bore, plating, port polish, case mods.

3 teeth added to the back sprocket or 1 tooth off the front will help.

 

[Sam Simons]

Re:yz125

Thanks,Rob for the info...yes,I can't expect much from less than 9 cu.in.,I know.....But,I don't like the 4 strokers,after 4
decades of riding 'smokers', I'll stick with this bike for a while longer(had it less than two weeks...)before giving it a new Zipcode. That,or yank the 125 mill and transplant a larger vintage piston port unit....I've done that before.
I've heard of Eric Gorr,I'll check for a website.

Any other 125 big bore users ???

Sam in Indiana

 

[robwbright]

http://www.ericgorr.com

The site is still down because he is moving shop locations. He is still doing work. He was Dr. Dirt in Dirt Rider Mag for like 20 years and if I recall, he's done about 40,000 cylinders. . .

Eric Gorr
Forward Motion
P.O. Box 69
Streamwood, IL, 60107
Tel.1-630-825-5645
ericgorr@hotmail.com

Try early in the morning.

There are several other guys with 144s here. Eric once built a 2002 RM 155 stroker.

 

[CRazy250]

just buy a 250 if you want more power

 

[robwbright]

just buy a 250 if you want more power

That depends on whether you want to race in the 125 class or 250.

Also depends on how big you are. I'm pretty small (5'4", 145 lbs) and I don't like the extra weight. My 125/144 corners a lot better than any 250 I've ridden - 2 stroke or 4.

A well tuned 144 will run 38-39 HP. A stock 250 2 stroke is normally in the mid 40s.

The peak power to weight ratio is pretty close.

 

[booneyscb]

check to see if you have the knarly pipe and short silencer. if not go back to stock. check the gearing final drive ratio of the sprockets. i usually go down 1 on the drive sprocket from stock. if yamaha had optional power valve springs they would be listed in the owners manuel. check with your dealer also.
renegade suspension can revalve your suspension for your weight and ability and woods usage. cutting down the seat could help also. erig gorr does the best job of big bore. and the best job of big bore for the money. the 144cc kit is the most economical. adds a lot of low and midrange. don't spend the money for anything bigger (stroking). to expense. would be better to buy a used ktm 200 instead. use kenda millville sticky tires for the best overall performance. kenda has a new 3:50 sized wider front tire that really helps in the woods. attend a riding school in your area too. learn how to make the 125 go faster in the woods is better than trying to tame a big bike without getting hurt. need more help, just post!

 

[Nevada Sixx]

i did alot to my 125, but best mod that actually mattered was dropping a tooth on the front sprocket. IF your bike is nothing like you want now, sounds like its time for a 250f or 200xc. Thing about low gearing, you cant go very fast down fire roads. but i can climb any hill on my 125 just about.