The $25 Bike, a 1974 Kawasaki MC1M 90cc motocross
Watch the video "Getting an old neglected bike running again" to see this bike up and running with some simple tips and tricks. Please leave a comment if you liked this video. Scroll to see pictures and descriptions and information about the restoration of this bike
Check out the bike I bought for $25. A 1974 Kawasaki MC1M 90cc. The MC1M is basically a stripped down MC1 for dirt and mini motocross racing only. The MC1M 90cc model was only made for 2 years making it somewhat of a rare model, however the bike shares a lot in common with its dual purpose MC1 (street legal) as well as some common engine parts with the earlier G3, G4, G5, and even the G31M Green Streak. Unlike the G31M Green Streak this was a lower horsepower more entry level racer for younger riders. Claimed h.p. is 6.5 where as the 10cc bigger Green Streak with its expansion chamber, cylinder porting and radical rotary valve timing made a whopping (claimed) 18 h.p. However some of that potential lives within the MC1M 90cc with some modifications. As stated before the model was only made for 2 years before being superseded by the KD80 and 100 motorcycles which built off the same platform. Most notably the model came with plastic fenders somewhat still a new concept for dirt bikes in the early 70's. Check out the "Getting an old bike running again" to see this bike run!
Here are the performance modifications specific to the MC1 (M) 90cc (from the Clymer service manual M350 seventh edition 1966-1980 rotary valve singles)
Check out the bike I bought for $25. A 1974 Kawasaki MC1M 90cc. The MC1M is basically a stripped down MC1 for dirt and mini motocross racing only. The MC1M 90cc model was only made for 2 years making it somewhat of a rare model, however the bike shares a lot in common with its dual purpose MC1 (street legal) as well as some common engine parts with the earlier G3, G4, G5, and even the G31M Green Streak. Unlike the G31M Green Streak this was a lower horsepower more entry level racer for younger riders. Claimed h.p. is 6.5 where as the 10cc bigger Green Streak with its expansion chamber, cylinder porting and radical rotary valve timing made a whopping (claimed) 18 h.p. However some of that potential lives within the MC1M 90cc with some modifications. As stated before the model was only made for 2 years before being superseded by the KD80 and 100 motorcycles which built off the same platform. Most notably the model came with plastic fenders somewhat still a new concept for dirt bikes in the early 70's. Check out the "Getting an old bike running again" to see this bike run!
Here are the performance modifications specific to the MC1 (M) 90cc (from the Clymer service manual M350 seventh edition 1966-1980 rotary valve singles)
What fits and what doesn't?
What follows are some general statements and information about what parts and bikes have compatible engines and parts. Kawasaki shared a lot of engine designs across many models and displacements. Some bikes all the change is the cylinder and head displacement. However there are some notable differences between the MC1 / MC1M (90cc) engines versus other Kawasaki models that are the same general displacement (90cc-100cc). The G1, G3, G3SS, G3M, G3TR, G4TR, G5, GA5A, KV100, G7, KE100 and MC1/MC1M all used virtually the same engine cases and most of the internal parts are similar (save for the parts that make a 90cc unique from a 100cc engine) with only minor porting differences, compression ratios, and carburetors. However that said most parts will interchange back and forth for example a G4TR (100cc) cylinder can be bolted on to a G3 (90cc) bottom end as dimensionally in how they mount are identical. The main difference with the MC1/MC1M bike is the fact that the exhaust port is offset to clear the single down tube frame, versus the other "G" and KE100 bikes having a double down tube frame where the cylinder has a centered exhaust port. So while an MC1 cylinder will fit a "G" and KE100 bike bottom end it cannot be used in those bikes frames as the tube will be in front of the exhaust port, this also works in reverse as a "G" cylinder will not work in an MC1 frame for the same reason. 
1974 Kawasaki MC1 M (before)
Below are various pictures from the restoration of the tank. First off here is what the tank started out looking like. Some dents, rust and obvious faded paint.
This step is sanding with a dual action (DA) type pneumatic sander after the first coat of filler is applied to get the shape back into the tank. This step will be repeated often until the surface is straight and has the correct contour.
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Common specifications for the MC1 and M models from the factory service manual (may apply to other models, check your specific model first)
Spark Plug NGK B7HS gap 7-8mm Breaker point gap 0.3-0.4mm Carburetor specifications Carb size 19mm Main jet 75 Pilot jet TBA Float height 24mm Idle mixture screw (turns out) 1 1/2 turns Fork oil qty 95cc No spark? Check your magneto coils (behind the flywheel) Magneto coil resistance values (for diagnosis) Coil/wire color/ ohm reading +/- 10% the MC1 has lights and battery the MC1M model does not Exciter red/white 220 Signal blue 75 Charging (MC1) blue/white .23 Lighting (MC1) Yellow .23 
1974 Kawasaki MC1M (after)
Restored Kawasaki MC1 M 90cc dirt bike
1974 Kawasaki MC1 M
This step is removing the vinyl graphics and rust with a stripping disc. Also identifying all the little dents and imperfections.
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