New Member, 2 stroke gearing/govenor ??

[007SwagBaus]

Hello all... so im building a mini bike. just something out of 3/4 12ga box tube...I have a motor out of a toro snow blower. its an R Tek 2 stroke 141 cc 5hp.

the manual says the engine is governed at 3800 rpm by "air vane"

does this mean there is no internal one in the motor and its limiter is the fixed carb? if i get a cheapo carb that i can throttle i'll be good? i see like chinese type ones for techumsa for like 15 dollars. the two bolt mounting looks to be the right size.


and then i found a gearing calculator what should i put in for the engine RPM? can this little sucker go faster than 3800 safely?

also im gonna go the jack shaft route. does anyone have any suggestions on what gears i could use?

this is mainly gonna be parking lot/ gravel. use so id like top speed. maybe 30 to 35 mph

 

[firemanjim]

The air van be taken off, and then you'll get more rpm. Not sure what these things will safely run to, but I'd say it was safe to assume at least 4500 rpm...
For gearing, we need to know how tall your back tire is. The best starting ratio for a mini bike I THINK is around 7:1, but with the 2 smoke engine, that might be the best bet anyway. The engine has no real power on the bottom of the rpm curve,its mostly in the middle and top.
to diygk....

 

[007SwagBaus]

I was gonna use harbor freight wheels... still cant decide on a size for the back. its either 10in or 13in.

i was thinking instead of doing like a 1 to 1 on the motor to jack shaft. i could gear that a little high to keep the rpms up. like 12t to 15t then like a 15t clutch to the 60t sprocket

 

[firemanjim]

Big no ! On the harbor freight wheels. They're crap! Buy a good wheel and tire. Your safety is riding on them tires. I think your life is worth more than $5..... Once you decide what tire you will use, we can figure out your sprocket numbers.
Let's say you go with a 7:1 ratio on a 12" tall tire..... 12 tooth clutch to 17 j/s in to 12 j/s out to a 60 axle.... That's 7.08:1... And your top speed would be 24mph @ 4800 rpm. That leaves you torque to mess around on dirt trails,small hills, and what not....

 

[007SwagBaus]

Oh wow. I'm not a stranger to HF quality but I assumed the tires would be ok.

Could you recommend a wheel? Well I can just do a search myself. A hub with an integrated brake would be cool. I was thinking about using the rear sprocket at a rotor

 

[firemanjim]

You can use the sprocket as a rotor too, but some people frown upon it..... I'm gonna do it on my sons mini bike.....

 

[landuse]

Here is what an air vane governor looks like. This is the one off my Briggs

 

[007SwagBaus]

ah ok. so it the air vane isnt a part of the carb itself. thats what i was thinking. A quick google search tells me its controlled by the air blowing off those cooling fin thingys lol.

Honestly i havent had the side cover off the motor yet as i was planning on just getting a 212 predator because the crank doesnt have enough shaft exposed to mount a clutch. But! I did see a guy use this very same motor with a jack shaft cause it is big enough so mount a regular sprocket to.

Thanks for all your help so far guys. im sure i'll have a few more questions in the future!

 

[firemanjim]

You can mou t a clutch. Its just gonna hang off of the crank a little bit. I can put a clutch on my 3.5 HP 2 smoke snow blower engine.....

 

[ML-TOYS]

I have a 5hp 2 stroke and it has a 1 inch shaft long enough for a clutch.

 

[007SwagBaus]

oh wow! see i've been doing a lot of forum surfing before i joined here and i was under the impression(from some posts ive read) that the clutch couldnt be hanging off the shaft.

knowing this now i guess im gonna ditch the jack shaft. im so glad i joined. thanks guys!