Anybody Build Go Karts?
Been working on a go cart project and need advice on gear ratio.Running a 10 tooth sprocket on the engine torque converter that I am pretty well stuck with,a 48 tooth on the axle and about 20 inch tall rear tires.It is geared way too high and struggles to get moving.I cant remember if I need a larger or smaller axle sprocket to lower the gear ratio.Somebody on here knows this. Thanks
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You will need a larger sprocket on your axle(the driven gear)to get a greater gear reduction(lower gear ratio). 0 -
Not knowing what size chain you are running, yes a larger axle sprocket will help. If you could possibly drop down to a 9 tooth on your clutch, it would help a lot more. Having trouble with getting it going will wear that clutch out. 0 -
As CBX said, a smaller diameter at the clutch will help a bunch.
A buddy of mine in high school built one using the variable speed running gear out of a snowmobile. That thing would flat MOVE! We paced him up to 80 mph one time before he chickened out and backed off.0 -
youtube...search grindhardpplumbing they build some bad ass go carts (barbie car) with sport bike motors etc...
https://www.youtube.com/watch?v=X1EHhgwA7SY
https://www.youtube.com/watch?v=5OPkZXUTNfo0 -
Aren't 20" tires a bit tall? 0 -
That's a nice ride FCD!
I used to go to some pretty nice Go-cart tracks in Miami back in the 70's. Good times. We used to stay when the modified class would come out and race. Screaming tuned two strokes. Just awesome.
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With such a tall tire, you will need a second shaft set up (jackshaft) if you have room. The second shaft will give you more options for gearing. You won't find much help on the clutch end of the gearing, so you are limited to making the change with the rear sprocket. I have included a calculator link below. Right now you are geared to run 171 mph at 3600 rpm.
https://www.bmikarts.com/Go-Kart-Gear-Ratio-Speed-Calculator
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Jack shaft setup would cost way too much for a fun kart. With a 20 inch tire you can run a pretty tall axle gear. Check American Power Sports. They used to have a fun kart section in their catalog.
www.apskarting.com
Eta: what size chain are you using? I can send you gear ratio charts for #35, 219, 428 & 503 -
I had a go-kart back in the 50s. It had a Clinton 5 hp engine, chain drive with a centrifugal clutch. I must have put a few thousand miles on it before the engine blew. Those were fun times back before you had to worry about cops taking you in for being on the road with a go-kart. 
My friend Jerry on the right in the photo had one just like mine except his had a belt drive. We raced everywhere we went.
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As said, a larger 'rear' sprocket is what you are after. A smaller engine sprocket will do the trick too, but with the output shaft being the size it is, smaller might not be able to be done.
Rule of thumb for sprockets is 3 teeth on the back is equal to 1 on the front.
On another note: I run a 4 cylinder 40 cu in racing outboard (water cooled) that will turn 9,000 rpm (depending on the propeller) @ a fuel/oil ratio of 8:1 (2 quarts oil per 4 gal of fuel). No one, and I mean NO ONE runs a two stroke (especially one that is air cooled) engine @ 12, 000 RPM on 60:1 fuel/oil mix. Or if it is done, it only for a short while. Racers that do that are automatically entered in the 'Bat out of Hell' club. As in - 'it ran like a bat out of Hell, for a little while'. BDTD.
Back when my dad raced Karts, 1960s, he ran an exhaust gas temperature sensor to keep an eye on combustion temp to see of the top of the piston was going to come out the exhaust. Today it is common to run a thermal couple under the spark plug as well as a gas temp sensor. But today's Karters are constantly 'tuning' the carb while racing.
Water cooling has been around for quite a long time. Back in the 60's water cooled outboard motors were adapted to some Karts for a specific class.0 -
I like this one. https://www.youtube.com/watch?v=IlRKTVGE_zg0 -
Figured you would check in Iceracerx. Good to see you posting. I know you have extensive two stroke experience.
Hope you are doing well.
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I'm using 420 chain. 0 -
FCD: According to McCulloch, the ratio for a straight 40 wt non-detergent oil for the 101A/B and earlier racing engines is 16:1, which works out to one pint of oil per 2 gals of fuel. 40-50 years on, one can imagine it would be easy to transpose 16:1 into 60:1. I hope you don't mistake these for 'fighting words'. It's just information.
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