Author Topic: Lil Smokey. 1975 Yamaha RS-100 Build  (Read 2444 times)

Offline pitobread

  • Posts: 21
Lil Smokey. 1975 Yamaha RS-100 Build
« on: Dec 10, 2018, 21:32:36 »
Hello All.  Long time lurker first time build thread.

A few years ago I Almost bought a Derbi GPR 50... this started a landslide of me wanting a 2 stroke streetbike that was small bore (I mess around with 2t scooters a lot) 

I found one, then another one of these 1975 RS-100.  Both rough, both non running, both without papers.

So I started a paper search and started tearing them apart.

After tearing them apart I saw a bunch of things I hated, terrible brakes, spindly frames with poor welds, 18 wheels so no real modern sticky rubber.  So I fixed all that, I put on some GSXR750 forks, laced up some modern wide 17" wheels to stock rear hub, and a Suzuki GT550 front hub, used some CBR1100XX rotors and a Suzuki Savage caliper along with a bunch of machining for spacers and bearings.

I also re welded the frame, stripped all the brackets that weren't needed, added new braces in weak areas and prepped it for paint. 

Fabricated a fancy torque arm for the rear brake with the help of Bruce.

Tail light bracket and plate bracket had to be fabricated out of aluminum for lightweights and also because the OEM one bolted to the now gone rear fender

Added a spacer yoke to the Aliexpress rear gas shocks.   Also around this time, went full ham and had every nut and bolt Zinc plated.

So up next was building an engine.   

I started with a set of RS-100 cases, and thanks to a 2strokeworld user had the port map for a 74 MX100 Cylinder.  They were tuned to 16HP from the factory where as this was only 12HP.

As it turns out the port timing is damn near exactly the same.

Now that's all and well but I want a little monster, so I started my battle plan.

I knew I wanted to use a modern piston to lower the crazy compression height of the stock piston...  I found that a KX100 Piston is .5mm bigger which was great because the cylinder needed an overbore.

I also added a DT175 Reed block and inlet boot with reed stuffer and a machined reed spacer.

The one difference Is though that the RS100 uses a way smaller reed block, so I had to extensively modify the inlet to get the DT175 reed block in it's home.

Next problem was though that the rod was too short, however Pro-X makes a KTM150SX rod that added 10mm to the total length.. which gave me this.

Durations after longer rod and removing 1mm from base of cylinder.

Some port work

Kx100 Piston in it's hole and after cylinder decking...

Cue up part 2....

« Last Edit: Dec 10, 2018, 22:38:35 by pitobread »

Offline pitobread

  • Posts: 21
Re: Lil Smokey. 1975 Yamaha RS-100 Build
« Reply #1 on: Dec 10, 2018, 22:02:13 »
I then needed an iggy and 12v lighting, as this was points and 6v. 

Started with a Honda Dio Stator, I have tons of these.  I turned the OD Down 1.5mm

Then I cut out a backing plate for the MX ignition pickup and the Dio backing.  I also cut one of the poles off the plate to make room for the pickup.

Then I had to rewind the stator.  Magnet wire and make sure you have the poles reversed every second one N/S/N/S in my case.  This achieved by reversing the winding direction every pole.  I have to tap in between two of the pairs of poles for my Regulator/Rectifier(Also off a Dio)

This upgraded me to a nice 12v ignition and the MX100 CDI, so I didn't have to use a points iggy.

Lighting got a full LED upgrade with cheapie bar end amazon indicators front and rear
Unfortunately I cannot get the direct link to my Instagram working...  but here is my main account.

at this point it was pipe building time.  I first made a mock up pipe out of paper.. I made a video about the formula I used to make this pipe.  It's from the ESE thread on Kiwibiker.

After some hammering and welding I ended up with this.

I did also go over it with oxy after because I like the gas welded seam look...  I'm a sucker for cosmetics.

Then we moved up to paint time.  Hit the frame with some Dupont 2k fleet gloss black

Fresh headtube stickers.

« Last Edit: Dec 11, 2018, 11:40:51 by pitobread »

Offline stroker crazy

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  • crazy as a fox
Re: Lil Smokey. 1975 Yamaha RS-100 Build
« Reply #2 on: Dec 10, 2018, 22:32:37 »
I'm in!

“Ride like the Wind” W.H.

Offline pitobread

  • Posts: 21
Re: Lil Smokey. 1975 Yamaha RS-100 Build
« Reply #3 on: Dec 11, 2018, 02:12:24 »
Well I had a long weekend.  Had a friend come and help me get the tins in color.  Still waiting for the first clearcoat to set and the decals to arrive. 

The clear isn't fully set but I couldn't help myself.

It's basically the factory color.  It will have the factory decals on there as well...

Offline JustinLonghorn

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  • Posts: 6651
  • No Purple Hearts, No Blue Ribbons
Re: Lil Smokey. 1975 Yamaha RS-100 Build
« Reply #4 on: Dec 11, 2018, 09:46:06 »
That's a righteous little scoot, man. I can dig it.
I'm going to eat your brains and gain your knowledge.

Into The Sunset, CB750 build

TT500 the Animal

Offline Hurco550

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  • Posts: 3917
  • Keep er' Between the ditches
Re: Lil Smokey. 1975 Yamaha RS-100 Build
« Reply #6 on: Dec 11, 2018, 11:19:03 »
this is awesome. Watching.
"If you just picked up a drug habbit instead of a kawasaki triple at least you could get high while you waste money"
~ bradj
1988 tw200, the swamp donkey:
2006 Suzuki DR650 Adventure monowheel trailer build:
1976 BMW R90/6 farkilitious:
1975 RD350 Road Racer:
1976 GT250 Rebuild:
Full Custom Pit Bike:
1971 Yamaha 90cc twin HS1:
"much ingenuity with a little money is more profitable and amusing than much money without ingenuity" - Arnold Bennet

Offline pitobread

  • Posts: 21
Re: Lil Smokey. 1975 Yamaha RS-100 Build
« Reply #7 on: Dec 11, 2018, 11:37:58 »
Thanks.  I have owned it for almost 5 years and these past few months I finally got my ass in gear to finish it.

I left out one of the best parts .

Nice audio clip of the exhaust and testing my home made ignition

Offline SF

  • Posts: 62
Re: Lil Smokey. 1975 Yamaha RS-100 Build
« Reply #9 on: Dec 11, 2018, 17:52:57 »
Sounds good man!

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72 R5
72/73 S2 RACE BIKE