2002 YZ125 Engine Mod's

[Combat767]

I'm looking for anyone who has information on modified 2002 YZ125's. My bike is stock, and I'm looking to get a little more oomph from the motor. I run the +30B class and motor size is of no concern. I am leaning towards a Pro Circuit port job, with pipe, silencer, and V-Force Reed valves. Pro Circuit has done quite a bit of work on YZ's for Yamaha of Troy, so they should have a pretty good setup worked out. I have also read of Eric's overbore kits. I am wondering if there are any 02 YZ125 owners out there that have done either of these engine mods. I am planning my mod's either this fall, or over the Winter. I love the wide smooth power band, but I need a little more for this 175 lb. small bore driver. I'm coming off of a 99 KX250 that was just to much motor when I got tired. I like to hold the throttle wide open, and you just can't do that on a 250 when you're tired and expect to stay in one piece :)

Thanks All!! :) :)

P.S. I'm curious to see how the KTM 200SX turns out. Maybe some of the Japanese manufacturers will consider a similar bike for all of us Vet Riders. :aj:

 

[MXP1MP]

I haven't had it done personally but so far everyone I've asked about it has said keep it stock. The general feeling was yes it was faster but it was harder to ride over stock. I hear from friends that carbon tech high tension reeds will shift the power band around alittle bit. Takes away alittle bit of the bottom adds alittle more top and allows for more over rev. this combo mated to a PC pipe/shorty silencer works great.

 

[RJH]

Your up early! They say a stock YZ with a pipe is like a modified anything else. Maybe add V-Force reeds for something to do. Also - I understand one of the Euro needles will give better flow than stock. In my opinion - the pipe and carb are what makes HP gains on todays engines. However - they say all the top pros run mod engines - they say. There is no end to jetting -drive around at medium speeds - for along time and get a feel of whats going on. Things happen in sand or clay or hills or ??? Bob hogg :D

 

[Combat767]

I plan to put in Delta V-Force valves first, and then a pipe and silencer before the snow flies. I'm curious what gains I will get in each of these two stages. If I find the power I'm looking for, I probably won't go the route of porting. I run an extra 2 teeth on my rear sprocket at this time. I read two articles in MXA a couple of months ago. Granted it was MXA and both bikes were YZ125's... but..... The Pro Circuit modified bike was able to run stock gearing. That's a pretty good power impovement. I wouldn't be able to afford all that motor work, but I think it would be perfect to get enough power to run one less tooth on my rear sprocket. The other article was a stroked YZ125, and I think it ended up being around a 133. It sounded like both bikes ran great, but if I can get the ponies with the least amount of metal removal (stroking, or overboring), I think I'd be happier. :) Thanks for the help so far.

 

[duner]

I had Eric Gorr bore my 02YZ125 to 134cc and port it. I asked him to give the bike more power everywhere, which he did. It pulls better from lower rpms, offers more over-rev, and is way, way easier to keep on the pipe. His prices are very competitive as well. Eric will work with you on getting you the most effective set-up to meet your needs. I wanted to keep my bike AMA 125 class legal, but having it bored further wouldn't have cost much more. I'm running the stock pipe. I've experimented with the FMF Fatty and Pro Circuit pipes, both of which gave questionable improvements to power before the porting, are significantly less effective after I had it ported. The stock pipe seems to be the way to go on this bike.

Before the porting I switched to the European spec needle; really cleaned up the jetting. A friend installed V-Force reeds ion his 02YZ125, which helped his bike a little, but nothing like the porting/bore.

 

[644]

Eric did a 144 motor :eek: for me and I run stock gearing and pretty close to stock jetting...depending on the weather/track. It didn't need any case work or grinding either! I run a fmf rev pipe and a shorty silencer and the thing rips :aj: Don't worry...I don't race in the 125 class, I am an 'old guy' ;)

 

[cr-man]

DEP pipe is the best pipe for the YZ 125 they work with a lot of yamaha teams in europe and everyone I talk to that has tried one loves it. FMF is the sponsor for yamaha of troy. I think if you get the pro-circuit pipe you are going to be unhappy unless you get all their engine mods. Good luck!

 

[whyzee]

Combat,
Eric did the 133 on mine as well as the mo-better porting, really gave an impressive low to mid with still plenty of top end power. Running stock pipe, 4 main sizes leaner and 1 richer on the pj. was running a 12 front but have gone back to the 13 sproket. Good luck.