OK....heres the plan

mdlee1958

mdlee1958

Member
Ok heres the plan, Yamaha RX50 engine on a Schwinn OCC chopper frame. Yamaha RX50 with 19mm reed block intake, Mikuni VM19mm carb, oil injection, with 22mm exhaust port and a 5 speed trans.
 

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Well .... somewhere along the way this build took a very odd turn. Somehow the Schwinn Chopper frame turned into a 1972 Schwinn Speedster. And then .... it really got out of hand. Just finished it's maiden voyage a few minutes ago and Holy Crap is it scary. The Yamaha RX 50 engine has more torque than the bike knows what to do with. May have to drop the rear sprocket from a 44 to a 36 just to keep the front wheel on the ground. Haven't even attempted to find out it's top end yet ????
 

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Wow I just saw your bike for the first time.
That little Yamaha engine is quite an a$$ kicking motor.
Rated at 7 1/2 horsepower and redlines over 10,000 rpm.
You've got your hands full.
Hope you are having a blast with your bike and don't get crazy.
Better beef that bike up before you rip it to shreds with that engine.
Now I want one, screw the Morini.
TiM
 
One nice part about the Schwinn Racer/Speedster framesis that the bottom bracket and head tubes are investment cast with the tubes welded to the stubs so they are a little bit stronger at those two points.
 
So far the only problem I've had is, with the weather being all over the place, daytime highs rangeing from 48 deg to 20 deg, the Mikuni carb has been a pain in the butt to keep dialed in.
 
mdlee1958,
WOW Looks great....
Cruiser bike handlebars create a very upright riding position.
Might need a lower riding position with that powerplant, putting more weight over the front end & improving high speed handling.
-Lowracer-
 
Already learned that on the hard way the first time I rode it. Dumped the clutch in 1st and wound up wheelie-ing the beast. Since the plan of this animal is to do LONG distance riding and not racing (those days long since left the dock, with my legs in hostage) I am just a little more "judicious" with the clutch and let her wind out slower. 40's are very obtainable with this bike and if you stay in the upper powerband have little doubt that the 50's are as well.
 
Thanks Tim, I used that one and the Mikuni manual to tune it in early November and she ran great for the week that it stayed in the 50's and then ....... "Frostbite Falls" hit Colo and the tuning went all over the map. Have been finding that any more than 10 deg change in either direction really messes with the carb settings. So the new habit is to stick a small screwdriver in my pocket every time I staddle the bike......LOL.
 
That bike looks amazing! Must be quite a kick to ride it places. If you ever get a chance you should put up a video of the beast
 
Hahaha that'd certainly be fun. I saw a dark green bike with a black motor on it today. Maybe some kind of flyer I'm not to sure, it was parked outside of cheba hut. Wouldn't happen to be one of yours was it?
 
Oh ok. I really liked it, should have gotten out to take a picture of it to figure out what kind of bike it is.
I wonder if the police around here are gonna be a little more on your butt now that it looks much more like a motor cycle with that yamaha :P
 
Well I've put over 300mi on it since November and they haven't given me any more notice than the other bikes. Also one nice part about the Yamaha engine is that it has 49cc stamped on the cylinder, so f they question it's displacement then I've got that covered.
 
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