MKL’s 1987 Yamaha YSR50 (December 2015 – Current)

MKL’s 1987 Yamaha YSR50 (December 2015 – Current)

The 1987 Yamaha YSR50 – How I lusted after this when I was a kid! I found this one purely by accident. It was left covered in a basement for almost 30 years, and had only 71 original miles! The purpose of these chronicles is to document my life and times with this classic two stroke mini-racer.

Photo Gallery

  • The YSR as I picked it up on December 25, 2015.
  • 12-26-15 - Initial teardown reveals the 50cc mill is clean and lightly coated in WD40.
  • 12-26-15 - The Mikuni carburator is fairly dirty, and needs a complete cleaning and rebuild.
  • 12-26-15 - The gas cap is rusted solid, and had to be pried off of the tank by force.
  • 12-26-15 - The gas tank was full of rust. This was the first load shaken out, but the final total was a whopping 7 cups! (Yes, I measured.) Oddly, not much rust is stuck to the inner surface of the tank, which obviously needs to be relined.
  • 12-27-15 - The original Yuasa wetcell. From the date code, it's 30 years old (!!). This will be replaced with a sealed cell.
  • 12-27-15 - Carb, airbox, and both switch control housings removed.
  • 12-27-15 - Intake manifold and engine case cleaned up.
  • 12-27-15 - A little more stripped down than yesterday, and a little cleaner, too.
  • 1-7-16 - NOS kickstand and hardware awaiting installation. Haven't found a spring yet though!
  • 1-7-16 - Draining 29 year old 2-stroke oil from the storage tank. Gooey, and purple!
  • 1-7-16 - The oil pump - looks virgin! I cleared the lines of the old sludge.
  • 1-7-16 - The OEM airbox. It's HUGE! Almost the size of a small car's. Awaiting modification, to allow for easier breathing....
  • 1-8-16 - Airbox rehab mod complete! 12 Air Inlets added for increased breathing capability!
  • 1-8-16 - Side view of airbox mod.
  • 1-11-16 - There are some instances where stock just won't do. The clunky stock clip-ons on the left are going to be replaced with the sexy aluminum models on the right...
  • 1-11-16 - NOS kickstand and gently used OEM spring installed. Now the damn thing can finally stand on its own two wheels.
  • Ace of Dents : Paintless Dent Repair NJ made custom tooling in order to repair the small dent in the YSR's tank without any repainting necessary. I was thrilled, because the stock paint on this tank is original and can now be preserved intact. Dent is shown on the left, and fixed on the right. The exterior of the tank is ready for a good compound and wax, after which it will be perfect - time to deal with the innards now.
  • 1-27-16: As if anyone needed more proof that there is nothing quite like Japanese steel, check out this beauty! The YSR's tank, neglected and left to rust for 30 years, has now been completely cleaned out with Metal Rescue, and relined with clear Caswell epoxy. It looks fantastic! One would never know there were once 7 cups of rusty flakes living in there. The white paint near the filler neck will clean up nicely too with some compounding. I'm wondering how to deal with the small gouges there. Not visible unless one removes the entire gas cap assembly, but I don't want those gouges to rust.
  • 1-28-16: Stock reeds awaiting replacement
  • 1-28-16: Boyesen #620 Dual-Sage Reeds installed with TC high performance reed stops
  • 1-28-16: Another view of the Boyesen Dual-Stage Reeds and TC Hi-Po Reed Stops
  • 1-28-16: Just arrived - the DG expansion chamber hi-po pipe.
  • 1-29-16 - Today's progress included checking fork operation. Everything was within spec and there are no leaks, so I'm keeping it simple and just changing out the 29 year old fork oil. Took a fair bit of research to find out how much and what type, since the service manual has serious errors in this section. For posterity's sake, it's 126cc in the left and 164cc in the right, 10 weight.
  • 1-29-16 - The stock Mikuni carb is now degunked, soaked, and spotlessly cleaned. New fuel line is ready to go on.
  • 1-29-16 - The innards of the Mikuni have been rebuilt, and a Dynojet Stage II kit has been installed. The ultra-thin Dynojet needle has the clip on third rung from the top, and down below the new main jet is a Dynojet #102. New OEM gaskets everywhere.
  • 1-30-16 - rebuilt the brake caliper today using all new OEM seals. The bore and piston weren't too cruddy, but now they're like new!
  • 1-30-16 - new aluminum clip-ons installed.
  • 1-30-16 - The carb is back on the intake manifold, the forks are back on with fresh Bel-Ray 10W fork oil, the D&G pipe is installed, and the 600cc worth of 30 year old trans fluid is changed to fresh 20W/50 Castrol GTX.
  • 2-29-16 - The bad news: Now that she runs, a minor oil leak has turned into a major geyser. The good news: It's a well known problem that is easy and cheap to fix. A flaw in the case manufacturing on 1987-88 models results in this clutch pushrod seal popping out of place over time, resulting in motor oil from the clutch dumping out all over the ground when the motor is in gear. A new seal and a dab of silicone will fix this in under 10 minutes flat. Two stroke simplicity! The YSR is off the road until the new seal arrives later this week.
  • 4-13-16: finishing touch! My new cylinder head temp gauge on my own aluminum brackets. Cool, eh?
  • The restored 1987 YSR50 on the open road in 2016 - GPS reads 53mph on flat ground. Ripper!

1987 Yamaha YSR50 Maintenance Log

November 13, 2021 – 711 Miles: Transmission Oil Change

December 24, 2018 – 481 Miles: Transmission Oil Change

December 25, 2015 – The YSR50 arrives at the stable with 71 original miles. See picture gallery above for restoration details.

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