Posts
209
Joined
4/11/2013
Location
MA
US
Edited Date/Time
11/29/2021 2:11pm
I picked up a YZ125 a couple months ago and started the cleaning and inspecting process. I also started collecting parts and researching forums for tips and ideas.
Here's what I brought home for $400
Among all the interesting things I found that PO had done to keep this thing running was an addition that may or may not have been a mistake. See the black dot on the tank? That's a .22 slug. Yep, it's 1/2 way embedded in the tank and the PO thought it was JB weld from the owner before him.
So-Far I've replaced all bearings and most seals. levers, grips, decals, airbox, side panel, Stator, Rotor, coil, and a ton of little detail things that were very wrong.
I'm almost satisfied witht he bike now. She still heeds the bars straightened and the DG silencer mounted. Sounds like a machine gun firing through a tin can...
One thing I may need help with is suspension: I can bottom the rear by jumping on / leaning back. And it seems to hit a hard stop sooner than I'd expext it to bottom. Has anyone here rebuilt these? I've got a 1979 IT250 for spares, so maybe I can build a better boinger from what I've got?
Any help / suggestions and hot setups from back in the day would be great!
Here's what I brought home for $400
Among all the interesting things I found that PO had done to keep this thing running was an addition that may or may not have been a mistake. See the black dot on the tank? That's a .22 slug. Yep, it's 1/2 way embedded in the tank and the PO thought it was JB weld from the owner before him.
So-Far I've replaced all bearings and most seals. levers, grips, decals, airbox, side panel, Stator, Rotor, coil, and a ton of little detail things that were very wrong.
I'm almost satisfied witht he bike now. She still heeds the bars straightened and the DG silencer mounted. Sounds like a machine gun firing through a tin can...
One thing I may need help with is suspension: I can bottom the rear by jumping on / leaning back. And it seems to hit a hard stop sooner than I'd expext it to bottom. Has anyone here rebuilt these? I've got a 1979 IT250 for spares, so maybe I can build a better boinger from what I've got?
Any help / suggestions and hot setups from back in the day would be great!
Oh, and the IT250 has taller suspension and a reservoir on the shock. Also has solid handlebars with no crossbar! Should I swap suspension????
I'm not a fast rider anymore, middle 40-C class racing my 1987 YZ490 against modern bikes. And I weigh 190 instead of the 145 that the bike was built to carry around.
OK, I think I just convinced myself on the suspension swap. Stay tuned. The 250 forks are good but need rebuilt. The shock is a big mystery: Supposedly it won't fit in the frame without some modifications to the frame. It needs a full rebuild as well.
MOTOR: The bike runs well, but seems to have low compression. I'm used to kicking over a 490, so I'm a little biased. I popped the pipe off and took a look into the EXH port. There's a brandy new piston in there! The PO told me it had a new top end before the ignition died, but that's what they all say.... So, it's either not even broken in or it was done wrong, or maybe the loose sparkplug has something to do with it... Like I said, everything was wrong with this one, but at least it was almost complete. The ports look bone stock too, which is great news. I can't wait to get in there and bring the porting up to modern specs.
I think the RM has 10-11 inches of suspension travel. My YZ has 9 I think, and I can bottom it with my arse.
The Shop
I think you will find the rear shock from the IT is longer than the 125 shock, and if it is you will not get it in there. I tried a slightly longer shock in mine, and it just would not work. Here is a pic of mine as it was sold with the 38 mm forks installed. You can see how far down I had them set in the yokes. This was as low as I dare take them and yes, the wheel did just touch the underside of the guard at full travel.
I've heard of guys installing 250 shocks, but having to modify the frame a little at the opening since the spring is larger in diameter. This is something that I'll be investigating. The shock on my parts bike is very rough.
What pipe is that on your bike? and more importantly, did you like it? And even more importantly, did you measure it?
Nice Hannah lightening stripes haha
I think you're right about the YZ turning capabilities. It always felt a bit reluctant to turn tight, unless it was just me.
The pipe is a Retro Rocket from Vintage Iron. Nicely made and good fit. Had to tweak the jetting a bit, the bike ran a bit richer with this pipe. Definitely a good pipe though.
I keep reading about the rear suspension, that it's weak and short. But also that the shock body is the same as the 250 and 400, but that it has a larger spacer in it that limits travel. I hope these shocks are rebuildable, or at least take-apart-able without too much hassle. Hopefully I can lengthen the travel and get a stronger spring to fit in the frame...
The previous owner has HD clutch springs installed and even with a new cable the pull was very heavy: unacceptable! I opted for the MOOSE RACING EZ-Clutch. It took a little work to get it right, but I do like the feel of the clutch now. It's about as easy as my YZ60.
Question: Has anyone here rebuilt the shock? The parts fiche doesn't ever show the shock exploded view for shocks. But All Balls Racing offers a seal head for this bike: P/N: 37-1116.
But hey, at least it won't sound like a chainsaw anymore...
Hopefully it has ignition timing specs, which is one of the things I need. I also reference the pictures in the manuals for wiring, cable routing and numerous other little details which have been messed up over the years of abuse. There's just so much on these old bikes that has been molested and done incorrectly. I'm amazed how some of these bikes even ran.
I think AllBalls offers a seal head and RT can set me up with modern valving.
I don't know where I'll find a piston or seal though. Any ideas?
Pit Row
I need an EVO bike.
I'll pick away at the rest of the bike over the winter, even though it's pretty close to being track-worthy. I'm even contemplating looking for a spare top end to modify, and a pipe or course.
Keep an eye out for me up there.
Mike
This build is being featured in the BikeBuilds.net directory here: Tdub13's 1979 YZ125 Race Bike
We're currently displaying only a reduced-size photo (similar to what you'd find in Google Images). We'd like to ask for your permission to publish the original full-size image with your build listing.
If anyone would like to have a build of their own listed, just send me a message with a link to the build thread and we'll take care of the rest.
Ken
The bike came out great. I'm very happy with the handling and suspension. The YZ250 forks with RT emulators gave some more travel and are perfect for MX. The rebuilt RT shock with the old school Luft reservoir works great as well.
The motor has good top end, but is lacking on mid and low end somewhat. I have a spare cylinder that I'm modifying doing some heavy work to, to bring it a little closer to modern specs.
Here's what it looked like at the beginning of this season. I raced it at Winchester MX, Wareham MX and even rode an enduro on it. The suspension was definitely NOT set up for the Enduro though. That was a rough one!
I'll post some pics of the cylinder in case anyone is interested. I'm not done yet and don't want to post ugly ports though! So you're going to have to wait a little while for those.
This picture is all I really had to go on when I found the reservoir. I think this was an LOP bike and there appears to be a White Bro's sticker on the reservoir.
This is my shock after rebuilding.
The Enduro's I raced were both Vintage. One was a "short course" which had 1 lap on a sandy MX track and maybe 3 miles of single track in the woods. It was a good hour long race each moto and it was grueling. I got 3rd in that one I think. I also raced a true vintage enduro that I placed well in. There were no trophies in that one so I forget if it was 2nd or 3rd.
Since then I've decided to run this YZ125 on MX only and let my YZ490 take me through the woods.
It's been a great bike so-far and it will be better for next season.
I also used RT Springs, spring adapter and bumper.
I imagine since it sits a little low stock its a really good turning bike.
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