1983 YZ125 Build

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2/19/2018 9:04 AM

Since i moved to Michigan, I've been itching for a new project but never had the place to do so.
Well I purchased a house last August and got married end of December. A few weeks ago, i decided a bike would be fun to build. It took me all of 4 seconds to convince the new wife we should rebuild a dirt bike together.

Originally, I was leaning towards doing a replica of the 93 Honda of Troy CR250 but decided if I'm going to go through the effort, having something a bit older with more character would be nice. I quickly zeroed in on the 83-85 YZ125's. Reviews say they were nothing special back in the day, but I liked the older styling while still having dual radiators like what you find on bikes today. Posted a WTB ad on craigslist and a few days later, I'm bringing this home.

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1983 YZ125. Seems to idle decently, forks are blown, brakes are purely for looks and airbox was missing (it did have a filter however). Seller did throw in a few parts, including parts to fix the brakes and forks, and an ebay airbox he picked up. Condition on that may not work for this build, but will take a deeper look at it soon and determine what I'd like to do.

As of now, i'm trying to identify the direction I want to go on this. I've liked the yellow graphics ever since I bought my 06 YZ250F anniversary edition back when they were new. I also am a fan of the white offered in other countries, last 3 bikes have all been white so that will probably be the route I go. It doesn't look like there is an easy way to get a white gas tank, everything else to make it white seems easy to source.

Before I start stripping the bike down, one tab is broken off the frame for the rear number plate. Should be fairly straightforward and easy to fix, so going to have a friend from work help me get that made up since I no longer have a welder. I also need to get the air box the seller supplied bolted in, to make sure all the tabs are still there. From there, strip it down and start powder coating parts if I've found a white gas tank by then.

We decided to set a budget to spend each month and go from there, budget per month is TBD. As of now, i'm thinking between $2-$300. Main priority is getting her student loans paid off, so this will be a bit slower of a build. As of now, i'm not planning on setting a total build budget, but build it how i'd like which may take longer with having a monthly budget in place.





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2/19/2018 10:31 AM

Looks like a solid bike! I have kicked around the idea of doing one of those myself. Check this guys website out if you haven't already. http://yz125k.weebly.com/

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2/19/2018 10:40 AM

My first new bike was a 83 YZ250. The bike did not get very good reviews but lucky for me I did not have time to read them as I was too busy out having fun on the bike!

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When in doubt gas it! It may not cure the problem but it will end the suspense!

2/19/2018 8:10 PM

Looks like a good solid bike, I just picked up the same model to start a 'rider' resto...mine runs great and is mostly intact, but some prior owner decided the 'update' to new Yamaha blue by spray painting all the plastic...with no masking, of course, so there's overspray everywhere! nothing a little elbow grease and some new plastic bits won't fix...good luck and enjoy!
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2/20/2018 5:03 AM

The '83 YZ125 was my favorite bike back in the day. I had YZ125s from 1980-1983, went to CR125 in 1984 which was a mistake, but the YZ125 in '84 was bad too... Should've kept the '83 YZ125 for 1984...

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2019 KTM 350 XC-F
Daytona Dirt Riders (DDR)
Floridatrailriders.org (FTR)

2/20/2018 6:05 AM

A good choice of bike. The K was the bike of choice between the K, L and N, as the latter two had performance and reliability issues. The K was made from old bullets and couldn't be killed.

When your checking over your frame, have a look at the area where the chain passes through. This usually wears thin and a small section of curved plate (a bit from some old steel handle bars) tig welded in works well. Also, the chain tends to grind down the cap on swing arm.

The 84 model 125 L chain guard is a better replacement, as it it went up and over the swing arm cap.
Keep an eye out for a DLS front brake plate. Its the 1 oclock style, not the 3 oclock tab style. This is the best brake upgrade you can do.

If your on a budget, i would keep the yellow plastics. Just really scrub, sand and polish them and i promise you the bike will look fantastic. A set of Wicked Tough tank graphics will set it off.

Forks seals are cheap and easy to fix. Race tech springs and emulators are a good upgrade and really stiffen up the front forks, but cost a bit. Rear shock can be a pain, as the body was not hard anodized and wears inside. Hopefully yours is OK.

The only upgrade to the motor i would suggest as a bang for your buck, is a power pipe. Jemco made a great cone pipe, but i dont think Jon makes them now. I have not heard good reports on the DG. I think Vintage Iron can still source them. Keep an eye on the power valve connecting rod and governor and make sure you get the correct adjustment using the notch in the linkage and hole in cylinder body. (check the online manual).

Your back tire looks flat. Check the rim under the tire for corrosion. Hopefully its OK. Looks like you need some bars and levers and grips which are a cheap upgrade.

Front number plate and mounts can be had from DC. If you want to dig into your budget, you can get white side covers that fit quite well from DC and if you ask them, they will custom make you some white radiator shrouds at no extra cost and only a few extra days wait.

I would just check, clean and re grease most bearings, linkages and the like. Save money where you can and spend it on stuff that is really needed. That rubber band that holds the shock reservoir on is rare. Add a tie wire on to it, so if it does get knocked, you wont loose it. If your tank fuel petcock is leaking, search Ebay as there are aftermarket identical ones with the tank o'ring that go for around $20. The carb should just need a clean, and you can get the spare genuine Mikuni jets and needles no problems.

Your radiators and hoses should be fine, but if one is fucked, then replace with Ebay genuine Yamaha parts, or the Chinese silicone hoses and aluminium radiators are good. Be aware that the K was the only model that had the cap on the left. The L and N swapped sides, so the radiators and hoses for those are no good.

Depending on what compression you have, you may need a rebore. Hopefully you are OK, and just a ring may need replacing. You can go up to 58mm with a Wiseco kit. Make sure the powervalve is ground to suit. Also, make sure you get a 58mm head gasket, which Wiseco does, but i dont think comes in the kit.

A lot of parts are still available from Partzilla and the like. These types of stores generally have all the parts diagrams. Just be aware that sometimes they show diagrams for the L or N and sometimes these parts are different. Also Ebay sellers tend to get some of the parts from the J mixed up. Some of these parts are different as well. Some parts that you may encounter that are advertised for the K, but wont quite fit are clutch baskets, water pump covers and that sort of thing.

Good luck with the build. Keep your budget in check by just scrubbing, lubricating, sanding, painting, polishing, checking, oiling and fixing most stuff. You have a great foundation to start with and when finished, you will have an awesome 125 vmx bike. The brochures advertised them at 88kg, and when you lift one on to a stand, it feels like a feather....

Cheers,

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2/20/2018 7:03 AM

jsks2 wrote:

Looks like a good solid bike, I just picked up the same model to start a 'rider' resto...mine runs great and is mostly intact, but some prior owner decided the 'update' to new Yamaha blue by spray painting all the plastic...with no masking, of course, so there's overspray everywhere! nothing a little elbow grease and some new plastic bits won't fix...good luck and enjoy!
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Not making any assumptions in your case, but in my experience, when bikes are hastily painted overall such as this, they were likely stolen.

Thieves would blast paint all over the bike to hide it's actual color so anyone looking for a stolen "Yellow Yamaha" wouldn't care to take a second look at a "Blue Yamaha" if they saw it running around out in a field.

A VIN check would set you at ease.

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2/20/2018 9:22 AM
Edited Date/Time: 2/20/2018 3:04 PM

I believe I found a white gas tank that is restorable.

Problem is, you have to be in NZ or Australia to purchase. Is anyone on here willing to help me out? I'll gladly pay pal you friends and family so you don't have to worry about losing money on your end from a stranger (or we can do another method you're more comfortable with), if someone can purchase and ship this to me in the US. Gladly will pay for your time involved with doing this for me.

Auction ends in a few days. There is a buy it now, so no bidding war.

Edit: White tank is on it's way! Found someone from another forum i frequent who volunteered to buy it and ship it my way.

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2/21/2018 2:18 AM

1983YZ125 wrote:

I believe I found a white gas tank that is restorable.

Problem is, you have to be in NZ or Australia to purchase. Is anyone on here willing to help me out? I'll gladly pay pal you friends and family so you don't have to worry about losing money on your end from a stranger (or we can do another method you're more comfortable with), if someone can purchase and ship this to me in the US. Gladly will pay for your time involved with doing this for me.

Auction ends in a few days. There is a buy it now, so no bidding war.

Edit: White tank is on it's way! Found someone from another forum i frequent who volunteered to buy it and ship it my way.

Glad you found someone to help, otherwise I could do it for you.

There's a whole bike for sale over here if you need a spares bike wink

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2/23/2018 2:55 PM

Tank is on it's way. cool Should be here between 3-10 days. Ended up being a way smoother transaction than I suspected.
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Bike is down to a frame, motor, radiators and triple clamps. Hoping we have time to get it the rest of the way torn down this weekend. Overall, the bike came apart extremely easy. Few bolts were a pain to get out, but we were able to figure it out and get it down to this within a couple hours.

Sorry for the dark photo, took it on my way in last night.
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I shot Eric Gorr a text message earlier today about rebuilding the motor for me. Waiting to hear back from here to see if this will be an option. He seems like a go to on these bikes from reading through threads.

I'm leaning towards powder coating the frame, swing arm, and lower fork tubes black. With the white plastics and red, I think this will turn out pretty good.

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3/4/2018 3:46 PM
Edited Date/Time: 3/4/2018 4:10 PM

Project 1 of the bike is complete.
Carburetor Rebuild. I used the Keyster kit from Ebay. Seller accidentally had the auction listed for 2 so he refunded half of my money. 2 parts did not fit my bike, guessing it was for the earlier model bikes (kit was for 78?-83), jets were slightly different but I knew this before ordering. Carb is very straight forward to take apart and rebuild, must less of a daunting task than the Aisin on my FJ40 i had rebuilt.

After a little research, i decided to pick up a little ultrasonic parts washer to see how well it would work to clean the carburetor. Overall i'm impressed with it. Parts need to be pretty decent, and you still need to at least knock off the thick grease/dirt caked onto parts but it does a pretty good job.

Have a new throttle cable on it's way to re-install and this will get buttoned up and stored until the build is ready for it.

Comparison Before/After
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Complete
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I've been trying to find a shop for the engine rebuild. So far, only 1 place had enough customer service to actually quote me... Price was a little higher than I want to spend so I'm going to continue looking. I'll probably have this shop rebuild my suspension, or at least anodize the lower fork tubes. I have not torn down forks/shocks before, so i'm a bit hesitant with my limited tools at my house right now, so I certainly need to research a bit more to make a decision.

Frame should get repaired this week if schedules line up with me and a friend.

Just realized my tire spoons are at my dad's a 1000 miles away. Accidentally left them in his truck I guess while we were riding in Moab. Need to get the tires popped off to break down the wheels for powder coat. Have decided, as of now, to tackle re-truing the wheels. Haven't attempted this before, but seems like a good learning experience opportunity and straight forward enough.

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3/4/2018 4:47 PM

Nice! My brother just picked up a 84 today...

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3/4/2018 5:47 PM

Redoing the motor shouldn't give you that hard of a time, just don't lose anything - take pictures especially of the shift star area, and take the transmission out in one peice. Paying a shop to split cases is going to kill you financially no matter what

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3/4/2018 5:54 PM

Only special tools you will need is a flywheel puller (like 20 bucks) and a 3/8ths impact gun. Pull the crank and have a shop replace the rod, unless you have a lathe a press a copper hammer and 2 dial indicators- and a need to learn to do it. I usually get charged about 200 when I drop a crank off. Heat the cases a little with a propane torch and pull the crank bearings out of the freezer and they will fall right into the cases, once you get the crank back heat the inner of the crank bearings and tap the crank in with a rubber hammer

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3/5/2018 7:02 AM

I sent my shock to Noleen for rebuild, valve kit, and hard anodize. Satisfied with the price, work and results. Turnaround - not so much. Check you shock body carefully before sending as they wear bad. Budget for fork and shock springs.
Check rims for cracks. Motor rebuild is simple. Should be able to find a local shop or local racer who would do it.
I race mine. It runs great and has been dependable. Mine is a white Canadian model - looks cool.

Good luck.

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3/14/2018 11:27 AM

Dropped off the frame & upper triple clamp at powder coating during my lunch break today. The coater estimated it would be ready for pick up in the next 2 weeks.

I think I decided against the white tank after all I went through to get it laughing
To go with the white, i wanted to do a few more things that would quickly add $1000+ to the already rapidly growing build. Hopefully selling the white tank for what I have in it won't be too much of a problem.

While the frame is getting coated, i've tasked my wife to get the swing arm cleaned & polished as well as the lower triple clamp.

I've found a place that can get me black excels. Wheels are going to have to go out to get built. Bit disappointed in that, but they have to drill them and need to do it all to make it work. They will also be powder coating the hubs and provided new SS spokes & nipples.

I still need to figure out what I want my next project to be. Forks need to get done, as well as getting all the bearings put back into the rear linkage so we can get that all ready to bolt up once we have the frame back.

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3/14/2018 5:28 PM

Did you send out your motor yet ?

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Yeah, I have no clue !!!

3/15/2018 3:59 AM

nicko-31 wrote:

Did you send out your motor yet ?

I have not. I have given up trying to find some one to rebuild the motor at the moment. Communication out of engine builders is absolutely terrible, not a clue how any of them stay in business with such poor customer service.

As of now, i think i'm going to shoot for getting the suspension done and a rolling chassis again, and then start looking for a builder while i work on the plastics/graphics.

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3/15/2018 6:45 AM

http://www.mxrestoration.com/1979CR250R.html give this guy a ring, Brian. He has done a 85 YZ 125 for me and I'm pleased with it. He also is working on a few of the same model one being his personal race bike.

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Yeah, I have no clue !!!

3/15/2018 7:16 AM

I did get pricing from him.
I completely forgot i ran across him somewhere else and shot him an email last week.

Labor is a bit high, he didn't give me pricing on parts. My other quote i received had about $650-$700 in parts, which puts both quotes around $1500-$1600 each if he's the same on parts pricing.

For a bike that will most likely not be ridden much if any, it's a good chunk of money but it's going to have to get done to finish the bike.

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3/15/2018 12:15 PM

1983YZ125 wrote:

I did get pricing from him.
I completely forgot i ran across him somewhere else and shot him an email last week.

Labor is a bit high, he didn't give me pricing on parts. My other quote i received had about $650-$700 in parts, which puts both quotes around $1500-$1600 each if he's the same on parts pricing.

For a bike that will most likely not be ridden much if any, it's a good chunk of money but it's going to have to get done to finish the bike.

$1500- $1600 ,Just for an engine rebuild?

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3/15/2018 1:00 PM

Brett Campbell wrote:

$1500- $1600 ,Just for an engine rebuild?

Correct. Which seems a bit high, but i've also never torn deep into these motors before either to know whats involved & costs associated.
That is part of the reason i'm holding off on building it until i can dedicate time to see if this is any where close to accurate or just way out in left field.

Price did include all new gaskets, seals, bearings, piston, rings, blasting cases, etc.

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3/15/2018 2:30 PM

Not cheap.When you factor in all the parts that will most likely need to be replaced it adds up really quick especially on hard to find parts.I did everything that needed to be done and some just for piece of mind. OEM crank ,all bearings,OEM complete clutch,Porting,bore,Piston ,Rings,Gaskets, on and on it goes. I have yet to even really ride the bike that much but when I do It's with complete confidence that it will hold together.

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Yeah, I have no clue !!!

3/15/2018 3:27 PM

1983YZ125 wrote:

I did get pricing from him.
I completely forgot i ran across him somewhere else and shot him an email last week.

Labor is a bit high, he didn't give me pricing on parts. My other quote i received had about $650-$700 in parts, which puts both quotes around $1500-$1600 each if he's the same on parts pricing.

For a bike that will most likely not be ridden much if any, it's a good chunk of money but it's going to have to get done to finish the bike.


You're getting pronged.

All my parts came to $490 (seals, Wossner piston kit, gaskets, rod, bottom bearings, reeds, clutch springs/plates, plug). $200 for a bore and crank rebuilt puts it at $690. I did the labor of pulling bottom end apart and assembly.
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3/21/2018 4:50 PM
Edited Date/Time: 3/21/2018 4:56 PM

Dropped my frame & triple clamps off for powder coat last week. Thought i would have a week or two before I got them back, took 2 days on the frame & upper triple clamp, and less than a day on the other triple clamp i had to do some work on first. You can see the new tab we had to fab up for the rear side number plate bolt.
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Over the weekend, starting cleaning up the linkage and the wife worked on the swing arm. linkage came out really good, swing arm is overall good, just needs a few touch ups where the mono-x sticker were.
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I gave Noleen's a call today. Very good prices compared to other 2 quotes i received, guy on the phone seemed very knowledgable & helpful, so i'm going to throw my forks & rear suspension in a pelican and ship them their way in the next few days for a rebuild. They will also be hard anodizing the front lower fork tubes, rear shock body & reservoir.

All of the suspension & steering bearings came in today. Ended up with All Balls kits. Seemed the easiest route to go to get everything I needed.

Ended up deciding on a color. Doing yellow tank & fenders, white number plates & black shrouds. I think the color combo is going to come out looking awesome with what i'm planning as long as my graphic guy doesn't flake on me.

Next projects are to clean up the gas tank and ship off all the plastics & tank to have the graphics made. Also want to start getting the swing arm ready to be re-installed, but trying to decide if i'm going to zinc plate a couple parts. Still trying to track down a place to do plating for me.

And if anyone hasn't noticed, the "monthly budget" plan has been thrown out the window. Don't tell my wife laughing

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3/22/2018 5:01 AM

Looking good!

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3/28/2018 4:07 PM

Headed to start my honeymoon tomorrow after work!

In preparation for 8 days away from work & home:
- Suspension is at Noleens for a rebuild and some hard anodizing
- Engine is at Tom Morgan Racing for a rebuild
- Gas tank is off at JSD racing for restoration

Still contemplating on upgrading to a DLS front brake. Will see if i can find a decent deal on one, have a couple ads posted. Probably will cave if it's going any thing like the rest of the build laughing

Waiting to hear back from my graphics guy. Leaning towards a copy of this but making it work for the yellow plastics & bringing back a bit more of a vintage vibe on logos/sponsors/etc.
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3/28/2018 5:52 PM

I'm interested in the bike shown here that has a Pro Circuit baffle. I didn't think that they ever made anything for that year and model. Also even though the radiators have opposite fill from my 85 weather the hoses are the same from 83-85.

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Yeah, I have no clue !!!

3/29/2018 3:40 AM

Exhaust took work to get them on the bikes.
Article on the 2 bikes (Same guy has a nice matching YZ100):
https://www.dirtrider.com/1983-yamaha-yz100-yz125-restored

Hoses and radiators are these which a few guys on here looked to have run. They have a set for the 85 i believe as well. I'll be ordering a set at some point in the near future. Sold an old remington model 32 i had picked up to play with so have some extra paypal funds to blow cool
https://www.ebay.com/itm/GPI-Aluminum-Radiator-hose-Yamaha-YZ125K-YZ125L-1983-1984-84-83-2-STROKE-new/253215068903?fits=Year%3A1983%7CModel%3AYZ125&hash=item3af4cb52e7:g:IAwAAOSwGIRXbOXB

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3/29/2018 5:28 AM

I have a brand new DG pipe for that bike if you need one.

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