Whats In the Shop

Evan’s 1975 Yamaha RS100 Project

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Evan’s 1975 Yamaha RS100 Project

Hi guys, Evan here.  If you haven’t noticed, I’m a bad writer. Horrible really. I’m an Engineer, and I’m very good at technical writing, instructions, etc. However, I’m embarrassingly bad at writing anything else, especially my own commentary on things. At least it feels that way. Anyways, I’m going to give it a try, and attempt to blog on here my low budget 1975 Yamaha RS100 project.  This will mostly be me rambling and making notes on what I’m doing, so don’t expect anything impressive. However, the pictures should be interesting!  Lets start off with some pics of the bike as I found her:

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The bike is a 1975 Yamaha RS100. It’s a small 100cc 2 stroke street bike. There’s not a whole lot of info on them online. I assume they made them through most of the 70’s, but honestly I’ve never seen one before. I picked this bike up at the Big 3 swap meet 2 weeks ago, while wondering around with my Brother Ian, Brady, and good friends Jordan & Katie.  I completely missed the bike on my first pass through the show. Katie found it, and was considering buying it, however she was very interested in the 1971 CL350 I had at the shop.  After a little negotiation with Katie, and the owner, and $600 poorer, I was the owner of a running RS100 with bad tires, no title, and 8 year old tags.

This bike is going to be a birthday present for my beautiful girlfriend (soon to be Fiance if I can ever get enough money saved up), Whitney. It’s not much of a surprise, she already knows I picked it up, but she doesn’t know how it will end up!  She got her license last year, and has a Virago 535. However she just doesn’t ride much on the street, she’s still very scared of the Virago. I think getting her on a much smaller and less powerful bike should get her comfortable around town quickly.  I think I’m pretty safe mentioning that here, as I doubt she will ever read this blog. If you are reading this, Happy Birthday babe….you just ruined your present! haha

After getting the paperwork sorted out, current registration and title on the way, I got started looking over the bike.  I haven’t even started planning the build yet, but first things first gotta see what kind of condition it’s really in.  It definitely needed tires (ancient dry-rotted Cheng Shin’s were falling off the rim) and tubes. It ran, but poorely (carb clean should take care of that). It may need a new top end (piston/rings easily available for these). I need to check the oil injection pump to make sure it works well. It needs a new battery (6V system, battery is shot, but charging system is strong).  Front brake lever perch is destroyed (wired together on the bars).

I went ahead and ordered new tires & tubes (Shinko SR241 dual sports)0000_shinko_sr241_front_rear_dual_sport_tire_--

They are super cheap and awesome tires. I’ve run them on my KLR650 and am really stoked on them for the price. I went with 2.75-18 size from Motorcycle Superstore, which is where I always buy Shinko tires.  I used standard BikeMaster 2.75/3.00-18 tubes.  I knew these tires were going to be too wide for the front at least, and probably the rear too. I’ll have to figure out what to do about that coming up.

 I also picked up a new brake lever mount on ebay:


So now I need to track down a 6V battery, get the tires on and ride the bike a little, and determine if I need to do a top end rebuild or not.

I got the tires on last week. I really appreciate small tires, swapping them & the tubes by hand with 3 tire irons was cake. Especially compared to doing a rear knobby on my KLR….ugh.  I had to remove the front fender to mount the tire, which I was planning on doing anyways. I may chop it up, or just build a new one. Not sure yet. The front fender definitely acted as a fork brace, so I think I will need something tying the forks together, especially with my fat ass tearing this thing around.  I’ll work on ideas for that later. I’m also going to start figuring out what bars I’m going to run. Jarred suggested low tracker bars, and I think that’s probably the right way to go.  Then on to the rear fender, deciding what to do with the airbox, seat, etc. Anyways, here she is now with new shoes:

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If you read this, comment on it! Give me some ideas, comments, questions, advice. Remember, I’m not the bike builder here, I’m the electrical guy! haha


  1. michael

    hey very cool post I bought a 1975 rs 100 a little over a year ago and have been looking for them online, with the same luck your having. im registering mine next week

  2. Chris Jackson

    I have a 78 cm185t with a bill of sale. The Oregon DMV says bring them a license plate. Last plate (CA) was lost in 1984. VIN is useless but I thought maybe you might have an idea on how to get this street legal. At 70 I am ready to get back on a bike. Thanks, from Chris.

    1. Evan

      Hey Chris, you can get it plated again. I didn’t have a title, just a bill of sale, and I got it plated . Is the bike last registered in your name? As long as you know the name the bike is registered to in the computer, you just need to file a duplicate/transfer title form with DMV and they will reissue a title.

  3. Guy Shields

    Hi…I have a 1975 RS100 purchased it certified in 2010 too many toys no time to enjoy….1573 original miles mint mint mint ..not sure the value “OR” if their is a market for this bike HELP !!! I live in Chatham Ont Canada

  4. Evan

    Hey Guy, from what I’ve seen there is not a huge market specifically for this bike. However, small old street bikes will always sell, especially 2-strokes…at least around here. Do you have some pictures of it?

  5. Leslie

    Hi Evan, ran across this site while trying to find some info about my 1975 Yamaha RS100. I bought it last autumn off eBay. I took it out for a short spin just up and down the street a few times (I’m a new rider) and accidentally ran it out of gas. Got new gas in it and rode it a few more blocks, then heard two loud POPS and it died. Haven’t been able get it started since. It seems like a pretty clean bike, and it started right up and ran well before I ran it dry. The battery is new. Can you offer any advice about what I might try next? Thanks! — Leslie

  6. Amee Abel

    I owned one of these, new, from the dealer. It was the most fun I could afford. And with me on it, it could hit 75 MPH on the highway (I was @125 lbs.) With a friend on the back, we kept to the back roads. I didn’t dare ride it from Long Island,NY to Boston, MA when I left home to go to college, so we folded down the handle bars and stuck it in the back of a Barracuda to transport it to school. My sweet bike was stolen from in front of my home in Jamaica Plain, MA–treat your beauty well and enjoy!

  7. Derek Nichols

    Hey Evan! I’ve been following the podcast since you started and never noticed this build thread. I have the exact same bike that I’ve been tinkering with on the side. It’s coming out to be a pretty neat little ripper.
    How’s this one coming, now that it has been a few months?

  8. Max

    Hey Evan, I`ve just recently started listening to your podcasts and it is just too interesting to listen to. Nice little project you found for yourself. I`m in Canada and I`m starting to repair my father in law`s motorcycle. It`s an old Honda CB175 from 1975. I was stored in a shed for 30 years and I took it out not too long ago looking forward to repair it and put it back on the road. Everything seems fine but I think the pistons are jammed. Any idea what I could do to fix that? Do I need to buy new ones or can they be cleaned and re-used? Please let me know!


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