Yamaha RX125 - Tracker


New Member
So I sold my CB250n Cafe bike about a month ago and bought a new project the next day. A 1979 Yamaha RX125 2 stroke.

Out with the old

In with the new.

The Plan with the RX is to build a practical and fun tracker bike with road/trail tyres.
I also wanted to build/make more parts for this bike than I have with previous bikes so the plan is for a custom stainless oil bag and stainless expansion chamber. I am still using a bought seat however.

I haven't had a lot of time to spend on the bike between having just moved house (Garage is an absolute shambles and currently doesn't have power connected), working away 2 weeks at a time and fitting in a weekend holiday however I managed to get a bit of a mock-up done.

This used to be a 20mm Stainless Bolt and Nut. Now it is an oil filler neck. (Can't take credit for this, a machinist mate turn it down for me on his lath)

I basically have a plan for the following:

- Stainless Oil bag (have the stainless stock ready and filler cap made)
- Cut back front fender
- Modified rear fender
- Tail light (Need to fab the mount)
- Seat Mount (Mount made, just need to weld to sub frame)
- Bars (Fitted)
- Tacho delete and running 2.5inch Speedo
- Dual stage foam filter (Fitted)
- Stainless Expansion chamber following the dimensions for a 1979 Yamaha DT 125 which effectively uses the same engine
- Longer rear shocks (Ordered 3cm longer)
- De tab frame

I am doing a complete assembly of the bike before stripping it back down to paint and powder coat.

Biggest dilemma I have now is with the electrical system. The stock bike is 6v and I would prefer 12v for the convenience of bulbs etc. I also have a speedo which contains 12v LED's for the check lights and back light. I can run a 12v step up for the back light but not the check lights. The bike runs a CDI for ignition.

Can anyone help with what will be involved for a 12v conversion or a way to run the 12v LEDs in the speedo on 6v electrics? I have a nice 12v lithium battery which would be easy to hide if it can be made to work.



New Member
These are the bars I used.



New Member
Did a bit of work on the RX in the last couple of days.

Built a work bench on Wednesday to make things a little easier.

- Fitted the new rear shocks
- Fitted the knobbies
- removed the centre stand
- Welded the seat mount bracket
- Welded the tail light bracket
- fitted the indicators and tail light

I need to trim the front fender before re-fitting it. Then time to start working on the oil tank


New Member
The headlight ring and plastic bucket were a bit damaged but I found a NOS set on ebay.
They went on yesterday as well as some new headlight brackets.



New Member
Hey, nice looking build.

Where did you grab the seat from? Was it much wider than the existing top rails? Ive finally got my shitty rx going and am weighing up the seat options..



New Member
Hi Chris

The seat is from Dime City Cycles. It sits pretty perfectly on the rails. I had to modify the front tongue sections to make them fit the rx and welded the rear mounting brackets on. I also used a little closed cell foam to support the seat on the rails.

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