Sprocket tooth count?

[That One Guy]

I'm still trying to decide what gear ratio to use on my go kart... I have an old 5hp Tecumseh, with a one inch shaft. Sadly the only clutch Azusa offers for the one inch is $124 bucks after tax and shipping, and only comes with one choice for tooth count-10 teeth. So, the only thing I need to figure out now that that has been decided for me, is the rear tooth count. It will mostly be in gravel, so wheelspin is an okay sacrifice for speed to me. Azusa offers from 53 to 114 teeth, so the deciding is tough. i figured I'd try for the happy medium, 73. Would that be alright?

 

[1992suburban]

why use a Azusa?
what size is your tires?
you runnin a jackshaft?

 

[That One Guy]

Because Azusa is kind of the only place I've been able to find solid drawings on what I'm going to get. My tires are lawnmower rear tires and wheels, I suppose that they're about 16". And what's a jackshaft?

 

[Russ2251]

With that size tire, a bigger driven sprocket is necessary...maybe in the 100-115 range.

 

[That One Guy]

Really? does it NEED to be that big?

 

[Russ2251]

Too small of a driven sprocket and the loads on clutch (especially) and engine will be too high. Somethings gonna burn or, (at the very least) have a shortened lifespan.
With an ungoverned engine should get close to 30mph with the larger sprocket.

 

[Kaptain Krunch]

Russ, with my old 5.5 tecumseh, and 15" tires i was running a 6:1 ratio, no problem at all, even with the crappy clutch and sloppy chain. 7:1 would be just fine with 16" tires as long as the kart isnt too big.

 

[Russ2251]

Not saying it won't work, but watch performance jump with the larger sprocket...especially on gravel.
Trial and error will prove out the large sprocket scenario.
Ever notice how much larger the driven sprocket is on a dedicated dirt bike than it is on it's equivalently powered street counterpart?
It's done that way for a reason...Torque.
If torque and performance is a non-issue, then by all means use the smaller sprocket.
Smaller sprockets eat HP.

 

[That One Guy]

I went out and measured, and they are 19". And I assume that a jackshaft is a solid axle, if so, then yes, I have a 1" solid axle.

 

[motor_head]

jackshaft is a separate shaft with 2 sprokets on it

 

[That One Guy]

Oh, nope. I do not have one of those.