Jackshaft ratio help, please

[fodhunter]

Here's what I have so far:
10" dia. wheel (4.10/3.50x4 tire) with 22 tooth freewheel sprocket;
9 tooth jackshaft out sprocket, WELDED on; 19 tooth centrif. clutch sprocket which was WELDED to the clutch drum (...I didn't do that!).

So what I need is the JACKSHAFT "IN" sprocket.
This push trailer will be driven by a 1989 B&S 4 cycle one cylinder 2HP engine operating between 2500 and 3000 RPM for a nominal road speed of 20 MPH. I really don't want to go much faster...25, MAYBE! I'm really looking for maximum torque to climb these bloody hills! I'm just shy of 76 years young and don't think these old bones will take much asphalt, so speed is not an issue.

According to various charts, graphs and tables it seems I need a 4:1 ratio OVERALL to accomplish
my goals. Therefore, I THINK I need a 31 or 32 tooth jackshaft IN sprocket .

Can anyone verify - or "poo poo"- these calc's for me?

I plan on using KMC Z410 chain throughout the system.

Best regards and thank you for any help or advice you might have.

Dave Hunter (AKA, fodhunter)
Prescott Valley, AZ

ps:
I've already built two friction drive bikes but want to try something different this time.

 

[keatonx]

If you arent already using this, google search "go cart speed calculator". Then you can be sure of your speed.
Also your engine will have a maximum governed speed of 3600 rpm, so that is the rpm you should put into the calculator. good luck!

 

[fodhunter]

Thank you, Kiatonx. Your input is well received . I have removed the governer so I guess I'll need to buy a tachometer. I wonder what RPM delivers the most torque?
fodhunter.

 

[Sidewinder Jerry]

Look your engine up online to get the specs on it.

 

[fodhunter]

Thank, "LR". It appears that 3060 RPM is the number I was looking for.
Do you know of a low-cost tachometer?
Fodhunter.

 

[Sidewinder Jerry]

I've got a tachometer/hour counter on my bike. I got it from Staton Inc.