Vintage Dirt Bike Q & A

I have a chance to buy a complete 72 SL100 really cheap. Any thoughts on how this bike would do in the 100 class?

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Terry Moody #48f
3x 74 Honda CR250M Elsinore
74 Honda XR75
73 Honda QA50
78 Yamaha YZ125E
78 Yamaha YZ250E
78 Yamaha YZ400E
79 Kawasaki KX250
79 Honda CR250R
79 Suzuki RM400
80 Honda CR125
2x 83 Honda CR480R
98 Kawasaki KX250

I had one, many moons ago, but I think mine was a '71? Reaching into the recesses of my foggy memory, I recall that it was a pretty smooth, bulletproof little ride on trails and the road. On the track, it wasn't real big on top end, not real quick off the line, and was only adequate in turns. The suspension left a lot to be desired. I was about 150 lbs when I had it, and even at my tender age at the time, it beat me up on any whoops, and bottomed out severely on anything but the smaller jumps. Never seriously raced it (just against some buddies on the practice track), and it was all stock. Didn't run it against any other 100's (other than it held its own against a Hodaka Road Toad once), but it wasn't any competition for the 2 stroke 125's that my buddies were riding.

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Steve Amling

1976 CR 250M
1980 Yamaha DT100G
1980 XR 200
1981 CSR650

I'll echo Steve's comments. I have bikes with both SL100 and SL125 engines and they sacrificed performance for reliability.

I've put ~$1,000 into one to make it fun but it now has a 200cc engine which would make it illegal for your intended use. I kitted an 85cc XR75 for my grandson that would leave the stock SL in the dust.

The stock SL engine only puts out maybe 5-6 hp, top speed maybe 45 mph, they are sprung really lightly. Unless you weigh less then 100 lbs, all this has to be fixed just to be safe. Stock suspension would bottom and buck you off first bump you hit.

So if you are just wanting something reliable to play with, congrats, you got what you wanted. If you are looking to play hard with it then you will need to change out most of the suspension and see if you can pump the engine up to 9-12 hp with porting, cam, carburetor, that kind of stuff.

The trick back in the day was the SL 100 bottom end close ratio with a 125 top end. The 150 kits had more low end, but cause the top end to suffer, so if it's a hilly track use the 150. If it's flat use the 125 top end. The 125 had a 21/18 wheel set up The SL 100 had a 19/17... yuk!
Lengthening the swing arm 2 inches helped, but you have to do major frame mods beyond that to get it to turn better.
Yosh engines had more power than Powroll, but both worked great!
Your gonna spend lot's of money if your serious!
Here at the shop we have a 1974 CR 125 with an SL 125 engine It wasn't cheep to build, but it is a hoot to ride!

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Proformance Cycle
c/o Lee Curry
58 Wyoming Ave.
Wyoming, PA. 18644
570-693-5811
mailto:proformance58@cs.com