Yz 125 head Upgrade?

[Guest]

Have an older bike I like to ride for woods racing. Rebuilding it! Is there any companies that make a head Upgrade for an 03 yz?

[mlatour]

Bud Racing: https://www.budracing-usa.com/us/dirt-bike-parts/engine/engine-parts/head-insert/cylinder-head-bud-racing.html

VHM: http://www.vhm.nl/?navi=cylinderheads

 

Have you ever measured & corrected the squish band on your stock cylinder ?

I reduced it a modest 0.20mm on my 2010 YZ125 without correcting the dome cc's.

it gained about 5psi of compression, from 180psi to now 185psi on a fresh top end

and made a noticeable difference on how clean & crisp it runs at lower rpms.

[Guest]

Dang I'll give that a try

[mlatour]

As mentioned I modestly left the squish at 1.17mm (minus 0.20mm from the stock 1.37mm) for future experiments

but 125's can run as little as 0.7 to 0.8mm, but likely requiring race fuel by then even with a corrected dome.

[Guest]

As mentioned I modestly left the squish at 1.17mm (minus 0.20mm from the stock 1.37mm) for future experiments
but 125's can run as little as 0.7 to 0.8mm, but likely requiring race fuel by then even with a corrected dome.

Well I don't run race fuel I just run 100% gas and mix it 32:1

[Guest]

As mentioned I modestly left the squish at 1.17mm (minus 0.20mm from the stock 1.37mm) for future experiments
but 125's can run as little as 0.7 to 0.8mm, but likely requiring race fuel by then even with a corrected dome.

It's time to do all that stuff tho because I've rebuild everything from the frame up it just needs a top end, to be adjusted a little here and there, and waiting on some clutch parts. It put my buddies 15 ktm 450 to shame a few weeks back, but it's geared really well for off-road and I'd say it's not the bikes lol!

[mlatour]

For woods racing I'm guessing you prefer low-to-mid power versus top end / over-rev?

 

I had tried some of the earlier all-fiberglass Boyesen Dual-Stage Reeds (not carbon) which did improve throttle response

but fell flat at higher rpms (not well suited for MX style riding), a shorty silencer will have the same characteristics.

[Guest]

For woods racing I'm guessing you prefer low-to-mid power versus top end / over-rev?
 
I had tried some of the earlier all-fiberglass Boyesen Dual-Stage Reeds (not carbon) which did improve throttle response
but fell flat at higher rpms (not well suited for MX style riding), a shorty silencer will have the same characteristics.

Yep. Bike has needed a top end forever, but it really hasnt lost much power and the bottom end on my bike is actually just scary powerful. I have a bunch of buddies with 250s and they are afraid to ride my bike! Haha but I really like how I adapted my riding style and how much faster I am than everybody, I have the carbon reeds and a fmf shorty as well! They add a bit of pep, the gold series fatty is pretty good but is more for top end, it helps bottom end too!