DIY Go Kart Forum

DIY Go Kart Forum (
-   Engines & Clutches (
-   -   Help...need to slow down. (

Toby from MO 05-19-2010 10:25 AM

Help...need to slow down.
Hey guys,

New to carting and I have a question about sprocket size…top speed. I bought my kid a used go Kart and it is way to fast for him…he’s 6yrs old.

The cart has a Tecumseh 6 horse (OHH60). Clutch is 12T and sprocket 80T (10” diameter)…15x6.00x6 tires. When I say to fast…I’m not exactly sure how fast it will go but I’m 240lbs and it takes me faster than I want to go…hitting top speed within a very short distance (maybe 15-20ft)…steering gets squirrelly quick…at top speed.

I’ve found several speed calculators and it appears the smaller I go with the sprocket the faster it will get. That said, I have not found a replacement sprocket bigger than mine…to attempt slowing it down.

How can I slow this kart down?

Thanks, Toby

Blazkowiez 05-19-2010 10:29 AM

Jack-Shaft gearing, you need to basically implement a 2:1 gear ratio reduction.

Toby from MO 05-19-2010 10:42 AM

Are there calculators available for figuring jack shaft gearing?

Is there anyway to govern the motor for less RPM's

Thanks for your help.

(His cart looks very similar to one in your avatar.)

robbie 05-19-2010 12:07 PM

You don't really need a calculator for a jackshaft. If you you use an 18 tooth gear to take the power from the engine and a 9 tooth gear to send it to the wheel, that would cut your speed in half. You could use any other 2:1 arrangement, or get close to it. I think I used a 17:11 on the kart I fixed up for my kids.

Toby from MO 05-19-2010 12:45 PM

Got it...Thanks. Simple enough.

You guys have any tips for the easiest install. I'm thinking space is limited with current configuration.

Current configuration includes:
Live axle…sprocket and brake drum mounted on keyed, double hub, just inside driver side rear tire. Engine sits just inside left side frame rail.

Is there an easy fit/install that allows motor/clutch & sprocket locations to remain in the same location?

Alternative options…
- move motor/mount towards center of kart…leave sprocket & brake drum in existing location.
- Leave motor in current location, leave brake drum in current location, relocate sprocket to right rear.

You got any pics of your setup you could post?

Thanks again, Toby

Toby from MO 05-19-2010 12:56 PM

Forgot to mention...the axle is not exposed. Axle runs width of Kart in square tubing...bearing on each end of tubing.

Looking for least amount of changes to current config. My kid is dying to drive this thing.

In the mean time I think I'm going to limit throttle travel and let him go.

anderkart 05-19-2010 01:05 PM


Originally Posted by Toby from MO (Post 98194)
Are there calculators available for figuring jack shaft gearing?

Here's one:

Fast Eddie 05-19-2010 01:28 PM

I think you may need to limit the throttle, not reduce gearing. You already have a pretty short gear ratio. What's the RPM of a OHH Tek, maybe 5K? With your gearing and a 15" tire at 5K RPM, you're only doin' 33 MPH. Limit the RPM to 1500, that'll get ya a solid 10 MPH. Then as your kid grows/gets more experience, you can increase RPM/speed. Plus you won't have nearly the fabrication of a jackshaft.

Besides, you think it takes off quick now, wait til you reduce the gear ratio 2 to 1. You could quite possibly pull the front wheels off the ground.

PS-If the kart is "dancing" around at higher speeds, check your alignment. Neutral or toe-out alignment can sometimes cause that. See pic.

devino246 05-19-2010 01:40 PM

1500 isnt enough to engage the clutch. Isnt idle around 1500?

Toby from MO 05-19-2010 02:18 PM

Not sure on engine rpm's...actually a question I was going to ask. Does anyone know? I typically punch in 4000 rpm on the speed calculators.

The Hillliard and/or Max Torque clutches I've looked at on line typically advertise 1800-2200 rpm angagement.

You this point I may attempt to limit trottle travel before I go fabricating. I've read in a few different places limiting throttle travel is not desired due to premature clutch wear...not allowing the motor to rotate at full RPM. That said, if so, I'd rather replace a clutch from time to time before spending a bunch of time changing something then change it back.

At this point I'm happy to have some options because last night I was left shaking my head when it carried me down the street at 25+ mph.

Keep the ideas rolling...I'll let you guys know what I come up with.

Thanks again, Toby

Blazkowiez 05-19-2010 02:28 PM

Most small engines are idled to 1800 rpm. These smaller centrifugal clutches begin lock-up around 2000 rpm and reducing the rpms with a pedal limiter will simply burn your clutch, this is why we suggest a jack-shaft.

robbie 05-19-2010 03:25 PM

I agree that you should install a jack shaft. It's not that hard to put together. You'll need some pillow block bearings, preferably the type that attach to the shaft with set screws. If you decide to move your engine, bolt the engine to the new mounting plate and THEN put it in place after your chains and gears are in place. In other words, build from the wheel, to the jackshaft, to the engine. That way you'll be less likely to have alignment problems.

Another point in favor of the jackshaft, you won't be likely to pop up the front end. The rear end will peel out before it ever lifts the front.

Eddie is right about checking your wheel toe-in if your kart is squirrelly. If it's set up right it should feel solid. But I think 30mph is way too fast for a little kid. I'm pretty sure our cart does about 12 mph top speed, and that's what it looks like when I'm watching somebody else drive. But when I'm the one riding it, it feels like 40. It will peel out and do donuts, and with no suspension it's a pretty exciting ride. A 6 year old at 20 mph sounds dangerous, or at least nerve wracking for the adult responsible for his safety.

You can order your jack shaft and parts from MFG Supply, or check ebay for sprockets. Typical jackshaft size is 5/8", and make sure you get the right size chain.

All times are GMT -6. The time now is 03:47 AM.

Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.