Centrifugal clutch won't let go

Hey All. I am new here. I am 90% done with my rebuild. I have a cart with a Ironton 208cc engine, 10 tooth centrifugal clutch, big Nobby rear tires, and smaller front tires. Here is my problem. When I pull the cord to start, the cart wants to go. I put it on jack stands to make my adjustments. I started it and turned the idle adjustment screw counter-clockwise till it stalled and the wheels were still turning. The throttle cable is not pulling when not pressing the pedal. I took the clutch off and tore it down, greased the spring and six curved pieces, snipped three coils off the spring put it all back together and there is no change. The clutch cover spins freely when the engine is not running. There is nothing rubbing inside. I am mechanically inclined. I would rather not take it to a shop unless I have to. So Please any suggestions are welcome. I will answer back to let you know if suggestions work or don’t. Thank you all.

Is it a new clutch? If not, my suspicion would be that the springs were overheated at some point and anealed, causing them to lose tension and lower the engagement point.

Cutting the springs might not be enough if that’s the case.

Sounds good to me. What measurements to I have to have as to buy the right clutch?

Chances are the engine is a 3/4” shaft. Can you nab a couple of pictures?

You can also get replacement springs for more clutches.

it is a 3/4" shaft and ten teeth. There is no brand name on the clutch, so I think getting a new clutch would be best. Also, there is a bluish hue.

Thats a max torque six shoe aka SS. Loads of guys race with those clutches especially for lower power 4 stroke classes. It’s a relatively affordable clutch, works fine and when I run them on my kid’s race kart, I put a stiffer spring in them for around $10.


Here is the setup I have. What rpm would you suggest?

Is the engine stock? If so I’d try the one around 2500 rpm.

I run the black springs at 3100 RPM but our race engines Rev to 6100, a stock engine like that governs around 3500.

Dumb question from a non wrench… aren’t wheels that big in the back needlessly eating power? That’s way more surface area than the engine needs, I would think.

Awesome, Thanks Jim, I will order the 2500 spring. Dom, Not taking this to the track, I am out in the stix and need off-road. No neighborhood, streets are backroads so people drive fast, but lots of fields to ride.

One more thing, get some sandpaper and sand the face of the shoes and the inside of the drum.

Not really. Like Charles said, this kind of kart is made for the dirt. You can overcome the gearing, but need the surface area to get bite on the unprepared surface which in most cases is loose dirt or grass. The taller tires also act like suspension to some extent sucking up the bumps.

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Gotcha. I suspect off-road karting would be a blast.

Did you know that in New Zealand, they combine off-road with sprint karting?

Here you go:

Note the mudflaps on orange suit guy kart.
I want in. This looks fabulous.

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No Doubt! I have so many questions. What engines do the run? Do they break up classes based on engines like we do? What kind of tires are they running? Do they use spiked tires like in Ice Karting? Going to need tear-off strips with all that mud flying!

Road trip when we retire? Maybe call up @Bobby and see if him and the missus wanna race. He’s close by.

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For Sure! I love the sound they make. Four Stroke Shifters! I am guessing they are off a MX Bike. Thought I heard the sound of a Two Stroke engine firing off when he got back to the pit area too. After backing the video up, I was able to get a better look at the other karts and their setup. Doesn’t look that different from a standard Sprint Kart. I would figure a taller ride height would be required or you run the risk of getting caught in the mud when the course gets rutted.

Because I’m curious, on the site it said this:

“By properly oiling your clutch you can avoid heat damage. When heat damage occurs, the clutch will never disengage and the machine will start taking off by itself as soon as you start the engine. You can see heat damage inside the clutch drum, the metal turns from black to a blue color. The clutch must be replaced if it has heat damage and won’t disengage.”

Having never had a centrifugal clutch, what usually gets damaged? Does the spring overheat and relax?

Update: I bought a 2550 spring and it still takes off. My question now is on my Ironton 208cc what is the rpm range? I have been searching all over and I can’t find the numbers. I replaced the spring, and the clutch spun free. oiled and greased everything. Installed it on the motor. Put the chain back on. Now it takes off on starting. I don’t want to keep buying parts that aren’t correct. Thanks for all your input so far.

How tight is your chain? I’d expect the engine to idle around 1100 rpm or so.

It is not tight tight, there is a slight bit of slack.