building a motorized bicycle, need help deciding on which motor should I buy?

6 horse, that's 3-4 times what a stock China girl makes.

The HP numbers I've seen for the stock 66cc china girl is between 2.5 and 3 hp... which sounds about right for a 66cc low output 2 stroker. A 40 to 50CC chainsaw motor puts out 3 hp and I have a Stihl and a Partner concrete saw: 66cc and 4.4hp for the Stihl and Partner is 71cc and 4.8 hp. At least one of these saws is going to donate it's motor to either a mini go kart or bike project.

For your info... Zenoah's are traditionally used in hobby applications like large scale airplanes and larger R/C boats, but it was/is the main engine supplier for go-peds which launched the gas power scooter genre. The basic goped for 23cc for 1.2hp but later uprated models appeared with same displacement and 2+ horsepower. 1 horsepower per 10cc is now semi-common place while maintaining nearly reasonable reliability.

My version of a Cadillac build might use a 62cc Zenoah which is around 5hp@ 7500rpm stock and weighs 5 pounds (however it's a $400 motor). Same motor can make 10+hp with aggressive porting at cost of ring/piston life.
 
The HP numbers I've seen for the stock 66cc china girl is between 2.5 and 3 hp... which sounds about right for a 66cc low output 2 stroker. A 40 to 50CC chainsaw motor puts out 3 hp and I have a Stihl and a Partner concrete saw: 66cc and 4.4hp for the Stihl and Partner is 71cc and 4.8 hp. At least one of these saws is going to donate it's motor to either a mini go kart or bike project.

For your info... Zenoah's are traditionally used in hobby applications like large scale airplanes and larger R/C boats, but it was/is the main engine supplier for go-peds which launched the gas power scooter genre. The basic goped for 23cc for 1.2hp but later uprated models appeared with same displacement and 2+ horsepower. 1 horsepower per 10cc is now semi-common place while maintaining nearly reasonable reliability.

My version of a Cadillac build might use a 62cc Zenoah which is around 5hp@ 7500rpm stock and weighs 5 pounds (however it's a $400 motor). Same motor can make 10+hp with aggressive porting at cost of ring/piston life.

newer ones might hit 2.5, yeah, but when I got into this stuff you were lucky to hit 2 with a stocker.

my money no object build would use a 50cc water cooled KTM. they make 9 horses at around 13 grand, 10+ is nothing with a good expansion chamber and some mild port work
 
5 pounds? Wow. Like to get my next one a little hotter . I was taking a survey. Another guy said he builds a China doll for $350. I'm trying to quests what a chiba doll weighs? 20 lbs?
 
Just buy a motoped

I think motopeds are really cool idea, but I won't ever have one for 3 reasons.

1. They are pretty expensive and for the same money, you can have a nice used motorcycle or streetable dirt bike.

2. In my state, Texas, or my previous home, Alabama, there is no regulatory advantage to a moped or motorized bike. If it has a motor and you ride it on the street, you must have a license... it sucks but don't see it changing anytime soon.

3. I don't want be seen pedaling something that really looks just like a dirt bike. Can't put my finger on it, but to me there is something different about a dirt bike that can be pedaled vs. a mountain bike with a motor.... maybe it's the old joke... two things you don't want to be seen riding.... mopeds and fat girls...
 
newer ones might hit 2.5, yeah, but when I got into this stuff you were lucky to hit 2 with a stocker.

my money no object build would use a 50cc water cooled KTM. they make 9 horses at around 13 grand, 10+ is nothing with a good expansion chamber and some mild port work

engine out of any 2 stroke ktm would be a great donor motor for a money no object project, but my ultimate off the hook motor idea would be this:

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXZRE9

weighs 12 pounds but has 21 horsepower... that's nearly turbine power to weight ratio.... doing a 30mph wheelie on a road or mountain bike is sure to surprise a few folks.
 
my money no object build would use a 50cc water cooled KTM. they make 9 horses at around 13 grand, 10+ is nothing with a good expansion chamber and some mild port work
Lance only paid $200 for the motor and he will be racing it
on Sat Oct 17th at Socal Motor Bicycle Racing.

10924623_10153019071128016_7598272462997500715_o.jpg
 
That bike is too cool...

...and is pretty close to what I've been kicking around in my mind... just been looking for the motor...

Is that a 4 or 5 cog gearbox?
It's a single speed centrifugal clutch motor.

Socal Motor Bicycle Racing does not allow multi-speed motorcycle engines to race
although Wolf Creative Customs built a 5 speed KTM.
 
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