Used Kart 4 kids is to FAST

[boyscout]

My neighbor bought a kart used home built kart for his 8 yr old and my 7 yr old. The issue is he bought it from the guy that runs our local "Lube Shop" that is into dirt track racing. It appears this cart was his sons introduction into racing. It's not a gear-box car or even legal for any track, but it is fast. My neighbor was under the impression it would only do around 20mph. Driving it home his oldest kid had it doing 35mph @ half throttle. He went back and asked the seller and was told they had it up to 58mph.

So, my issue is I have to slow it down. I haven't gone to talk to the builder/seller yet. I'm told it's a 3 speed automatic. You can "feel" what appears to be a shift along with a increase in speed when driving it. There are no size markings on the motor, but based on size I would guess 8-10hp. I can not find anything that resembles a tranny. There's no visible torque converter or jack shaft. It does have what appears to be a differential on the drive axle.

I know y'all need some pics to help. So, pics to follow today.

 

[boyscout]

Here's the pics. I'm open to all opinions and info you guys in the know might have.

 

[ramairgtz]

I call BS on the 58mph top speed from the looks it probably does 30 maybe 35 tops. Easiest way to slow it down would be put some kind of stop on the throttle cable to limit how far it can be pushed down

 

[boyscout]

I know for a fact w/ a 140lb (I'm guessing) person in the seat it did 35mph on pavement not at full throttle.

I drove it again today (and I look like a 200lb trained bear in that tiny thing) and I didn't feel any shifts just a build in speed. It doesn't spin the tires, but once it's rolling it takes off. Compared to my 4-wheeler I was doing around 25-30mph. I'll use my gps to find out next time.

Found the governor pin and think the builder removed the internal gears.

 

[slideways]

That is the weirdest clutch setup i've seen. Has a brake band on it? So slowing down essentially is trying to stall the motor?

I agree that slowing it down is going to be tough. Gearing it down would be a better idea but gears are hard to find to fit those diff boxes. So unfortunately throttle limiters would be my choice. The only problem with them is that they can kill clutches since they dont allow the motor to rev up and engage in.

 

[redsox985]

A band brake one the motor isn't the safest idea. If the chain snaps or pops off, you have no brakes.

 

[porsche930dude]

looks liek a briggs 8hp with a centifical clutch so yeah theres no gears. I wouldnt doubt that that thing scoots i have a similar cart. lower gearing wont really help slow it down it may even make it faster. I know that makes no sence but its true. The only good ways to slow it down is to limit the throttle movement or get a smaller engine like a 4 or 5hp and put the big one on the shelf till they get bigger. thats what i would do if i were you

 

[Doc Sprocket]

I'm gonna jump in and disagree with Porsche. Lower gearing WILL slow it down, but you're going to require a jackshaft setup. You need to gear quite a bit lower, not just a few teeth. Furthermore, I do not agree that limiting the throttle significantly is a good idea. Unless you adjust the throttle stop using a tachometer, you run the risk of limiting the RPM to lower than the clutch lock-up speed. This will result in the clutch always slipping, and burning out prematurely.

Unless somebody knows something I don't, then no- that's not a three-speed.
Look towards regearing, and even smaller diameter rear tires. As a starting point please provide us with the tire diameter in inches, the number of teeth on the clutch sprocket, and the number of teeth on the axle sprocket.

Also- I do believe the "projected" top speed you currently expect is either a mistake, or the governor has been defeated, and it's running well past 3600 rpm. Got a GPS? A tach would do you a world of good, too.

PS- That differential looks exactly identical to the one I put in my kids' kart- came off an old lawn tractor. I believe the original sprocket was 60T.

 

[slideways]

I can see that the tires look like 15x6 lawn mower. Appears to be a 10t driver. Those diff pattern gears only come in like a 40t and a rough count of around half looks like 18 teeth i can see... assuming that the differential is geared 1:1 which most are the speed calculator looks like:

3500rpm=15.8mph
4500rpm-20.32
5500-24.83

If the thing is tweaked to run more than 6000rpm i'd put it in a bulletproof lexan box before my kids rode it again lol.

 

[boyscout]

clutch sprocket - 10
axle sprocket - 54

After reading the "5hp governor removal" thread on the forum I do believe it's been defeated. Now I wish I had grabbed my gps because for mine and all your sakes I have to know how fast I can get it.

 

[slideways]

18.4 @ 5500
15.05@4500
11.71@3600

I'll be the first to say that these calculators are off a tad. According to the tires and gear on my race car it says it goes 40mph on a track where they are certainly over 70mph on the straights

 

[Doc Sprocket]

Don't go by rated tire size, measure the tire's radius from the ground, and double that number for diameter. Slideways, I have that exact diff and the factory gear was 60T, I just checked it.
With an assumed 14" tire diameter, 5.4:1 ratio, and 5000 RPM, I'm calulating 38.5 MPH. Let's not forget that "half throttle" according to your foot does not mean it actually has the potential to double the speed. Horsepower, weight, drag, gearing, etc all play a part, too.

 

[slideways]

Yea they just don't make every size in that funky pattern

 

[Doc Sprocket]

No. When I regeared, I had to grind the diff webbing down a little, then take a standard weld-on sprocket and drill that particular 2-and-2 pattern in it.

 

[slideways]

Fab skillz lol. What kind of motor is on that thing? Don't recall seeing a muffler like that before.

 

[Doc Sprocket]

My pic, or boyscouts? The engine in my pic is a clone of a Kohler (I believe).

 

[boyscout]

I have no clue about the motor make, model, or size. There are no badges or plates to get any info from. I didn't snap a pic of the electric starter on the motor. It looks like a car starter with a pulley adapted to it.

 

[slideways]

No i was talking about Toystorys.. i didnt know it wasnt your kart.


Boyscout i think you have an 8hp Briggs. Model number should be on the tinwork either on top next to the spark plug or toward the seat.

 

[Doc Sprocket]

It is the kart I built for my kids.

 

[theo]

Seeing it has a roll cage, I would install a 4 point harness.