Pwk 38mm in 2006 yz125?

CaveMike get new to him 2006 yz125.  Carb be Mikuni tmx 38mm.  It be leaking and need rebuild.  Maybe float problems, maybe needle jet.  CaveMike going rebuild it, keep fingers crossed.  CaveMike have extra Keihin pwk 38mm from 2005 yz250 laying around.  Him thinking about use pwk in 125.  Anyone do this?  

Hi Cave Mike,
I have not seen any of your posts in a while, but I'm glad you are back! I have also recently acquired an 06 YZ 125 (last May). The bike is so much fun that I have only ridden my 250 twice since acquiring the 125. If I remember correctly, you are more of an off road guy than one of those fancy MX guys. A few tips you might find useful for your new mount:

1. Don't screw up the stock carb. I bet your problem is that ethanol has damaged the tip on the float needle. Replace it and see if that solves the problem.


2. My advice would be to do whatever it takes to run the stock carb with the YZ, as it has the best throttle response of any 125 I have ever owned, and I've owned plenty.  Stock jetting is a little rich on mine for my elevation and woods riding.  I found the best combination was the accessory needle (1/2 step leaner) with otherwise stock jetting, and an "8" (NGK BR8ES) heat range plug.  Leaner pilot and main jets ruined the initial throttle response.  I just put a "9" plug back in when I ride with the fancy boys on an MX track.  


3. Wiseco piston at 32:1 works well.  I just replaced the current Wiseco piston at 95.5 hours (crazy, right), but it looks great.  Hours 93 to 95 on that piston included winning my class at a regional hare scramble.


4. The stock suspension, after being sprung for my weight, was atrocious on eastern single track. I had an off - road revalve done (SoPro in Tennessee) and now it is sweet!  Best money you can spend in my opinion.


5. A Twin Air filter fits better in the airbox, giving you a little more room to operate.  


6.  Budget for parts, and check the bike very carefully after each ride.  Maybe it's just my particular bike, but it seems like every time I ride it, I break something.  Water pump seals, cable guides, pipe springs and mounts, spokes coming loose.  Nothing major, but this bike seems to break more little things than any bike I've owned in recent memory.


7. If you change the gearing, confirm with lap times.  The conventional wisdom is to "gear down" but I actually found my lap times were faster with stock gearing on single track, screaming the snot out of the bike in first gear a lot.  I guess it just depends on local conditions.


8. Repack all bearings.  The yamaha factory must have a grease shortage.


Enjoy the new ride!

Edited by rpt50

No it's not a grease shortage it's about shipping rules so they use assembly lube. Part of the dealer setup fee for a new bike is supposed to have the bearings greased after they receive the bike. But 99% of buyers don't do anything about it and the dealer hoses you and pockets that fee.

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