Another new guy with possible centrifugal clutch issues

[digitalsdc]

Hi All,

I just purchased a used (about 3 years old) Smart Kart with a 6.5hp clone engine. This was formy son's 12th birthday. I believe it has a centrifugal clutch with chain drive. I could post some pictures later if that would help.

I've already cleaned the carburetor and the engine seems to run fairly strong now. The problem now appears to be in the clutch. I'm just guessing that it's somehow stuck in a high range because when I try to accelerate, the kart barely moves but it will eventually speed up on a flat surface. Once going, it will pick up speed, but there is almost no low-end torque. Trying to go up a hill just kills the engine.

If I raise the back end off the ground and run it at idle, the wheels quickly accelerate to a pretty good clip and I can accelerate up to full rpm.

I haven't investigated anything about the clutch yet and was hoping to get some helpful tips here before digging into it.

Does anything stand out as an obvious clue?

 

[OzFab]

It sounds like your gearing might be off. Count the teeth on both the clutch & the axle sprocket & get back to us. Go ahead & post some pics as well...

 

[r_chez_08]

May be gearing issues. Post pics along with rear tire diameter, rear sprocket teeth number and number of teeth on the clutch. And if there is a jackshaft, post the teeth numbers on that too.
Edit: balls, fabroman beat me to it!

 

[dmaznic]

yes, gearing. if it was a clutch problem, you would hear the engine revving up without the kart actually going anywhere

how about the engine size? driver weight? passengers?

 

[OzFab]

Edit: balls, fabroman beat me to it!

Lol, close but no cigar

 

[r_chez_08]

Lol, close but no cigar

Atleast I still got a 'thanks' for writing pretty much the same thing

 

[Doc Sprocket]

If the clutch were stuck partially engaged, you would not be able to stop the kart without stalling, or start the engine without moving.

One thing worth looking into- oftentimes, we see people who have purchased a used kart with poor gearing. A leading cause of this is when the original owner does not maintain the CVT and it stops working. Instead of repairing the CVT or a costly replacement, they just bolt on a much cheaper centrifugal clutch and call it done. The problem is that they don't alter the reduction ratio to suit the new circumstances. This may not be your problem, but you might want to research the model you bought to find out if it originally shipped with a CVT.

 

[mlear92]

my cart is having similar problems. i even replaced the engine and got a brand new clutch. but now when i accelerate, my clutch gets real hot real fast and starts to smoke some.
any ideas? i havnt put any oil on it but its brand new. does it need to still be oiled? my axle sprocket has 60 teeth and my clutch has 10 teeth. both motors were 5hp.

What is a CVT?

 

[digitalsdc]

OK. Thanks to everyone for all the responses. I'm sorry it's taken me so long to get back with some details.

Here is what I've done so far:
1. I took apart and cleaned the carburetor and other accessible parts
2. I removed and cleaned the fuel filter in the gas tank
3. I cleaned the air filter
4. I replaced the fuel with fresh gas
5. I changed all the oil.

Results - the engine runs strong, though I've still got to make some adjustment to the linkages. By the way, does anyone have a photo of how the linkages SHOULD look on a GX200 clone?

Now, to the clutch and gearing. The small sprocket has 10 teeth and the large (on the axle) has 50 teeth. The rear wheel has about a 16" diameter.

When I take the clutch off, it seems to spin freely, but you can see from the pictures (hopefully) that it's very rusty.

Here is some symptom-type information:
1. When I run the engine with the back end off the ground and the brake released, even at idle the wheels are turning fairly quickly. I try to adjust the idle downward but it starts to sputter so I feel that's as low as it will go. The wheels never do stop turning.
2. At idle (as above) if I brake the rear wheels, the engine will die. However, if I start the engine with the brake locked, the engine will run, but it chugs quite a bit and when I try to accelerate it often sputters and dies (particularly if my acceleration isn't very gradual). This may be due to an old, rusted out clutch (see pics). If so, and I need to replace it, does anyone know what I should replace it with and where to get it?

3. Unrelated to the clutch, when the back wheels are allowed to turn freely, if I accelerate via the standard throttle cable (connected to the long silver rod), I get very little acceleration and even then it starts to vary RPM. I assume that's the governor doing that? If I accelerate via the direct throttle arm on the carburetor, it accelerates nicely and stays at a constant RPM. Is this all due to the governor, and if so, is it recommended that I remove it?

Again, thanks to any and all with insights. I'm sure this is basic stuff, but it's still a challenge for a Newb.

 

[Jcotz]

"Now, to the clutch and gearing. The small sprocket has 10 teeth and the large (on the axle) has 50 teeth. The rear wheel has about a 16" diameter."

Totally aside from the clutch, this could be a problem. This may be overworking the clutch and leading to further clutch problems. I would recommend either getting a bigger axle sprocket or smaller tires.

 

[Doc Sprocket]

my cart is having similar problems. i even replaced the engine and got a brand new clutch. but now when i accelerate, my clutch gets real hot real fast and starts to smoke some.
any ideas? i havnt put any oil on it but its brand new. does it need to still be oiled? my axle sprocket has 60 teeth and my clutch has 10 teeth. both motors were 5hp.

What is a CVT?

Continuously Variable Transmission, also known (somewhat improperly) as a TC or Torque Converter.

Clutches should NEVER smoke! Either you have excessive drag like a seized brake or bearing, or your gearing is too high.

 

[OzFab]

First things first: gearing is way off. 5:1 with 16" tyres is way too high; you need to change your axle sprocket to at least 60t, maybe even 72t (with tyres that big I would go for the latter or somewhere close).

Accelerator: you don't have enough leverage from your cable. See if you can figure out a way to move it further along the arm.

Now to the clutch: when mounted, the outer drum should spin freely; is it? If not, clean the bush with light emery & coat it with oil, that should free it up.

Do all that (in reverse order if you like) & let us know what happens

 

[digitalsdc]

Reverse order then...

Clutch: the outer drum does spin freely while engine is not running, but only occasionally while it is. I haven't taken it apart, but I'm thinking maybe the spring is shot or something?

Accelerator: thanks for the suggestion. I'll play with that one a bit.

Gearing: thanks for this suggestion also. Do you know where I can get such a sprocket? Would it be the same as any dirt-bike sprocket I could pick up at a dealership or are they completely different?

 

[digitalsdc]

I just had another thought regarding the clutch. I read somewhere that if a chain is too tight it could have a similar effect - the kart moving when idling. The chain really is tight, but I'm not sure how that would cause it. Any thoughts there?

 

[Doc Sprocket]

Yes- too much sideload on the bushing. Loosen the chain so it will deflect maybe 1/2" with your finger.

 

[Bluethunder3320]

it most likely had a CVT, i would get one for it anyways. it would change both take off and top speed by a lot.

 

[landuse]

Gearing: thanks for this suggestion also. Do you know where I can get such a sprocket? Would it be the same as any dirt-bike sprocket I could pick up at a dealership or are they completely different?

You need the same pitch sprocket as the one that you have on your clutch. You need to measure the distance between 2 teeth. This will give you your pitch. Have a look here then

http://en.wikipedia.org/wiki/Roller_chain#Chain_strength

You then go out and buy a sprocket with the same pitch

 

[digitalsdc]

Ok, I loosened the chain as prescribed and the result is the same. The engine is now running and accelerating strong so I've pretty much determined I need to replace the clutch, sprocket and potentially chain (to get a better ratio).

With that said, I'm wondering if a CVT really is the best option or of a centrifugal clutch is adequate for a 12 year old and friends. There's a pretty significant cost difference but I don't know if the performance difference merits the cost.

Any opinions on that? And thanks again to all for your responses.

 

[landuse]

Ok, I loosened the chain as prescribed and the result is the same. The engine is now running and accelerating strong so I've pretty much determined I need to replace the clutch, sprocket and potentially chain (to get a better ratio).

With that said, I'm wondering if a CVT really is the best option or of a centrifugal clutch is adequate for a 12 year old and friends. There's a pretty significant cost difference but I don't know if the performance difference merits the cost.

Any opinions on that? And thanks again to all for your responses.

The first thing you need to do is change your gearing. If you have a 72T sprocket, then I do not think that you will need a CVT. Even though a CVT will make a huge difference, the centrifugal clutch should work fine (and its cheaper). You need to change your gearing though. You will need a longer chain if you get a 72T sprocket.

The clutch you have at the moment might just need new springs. The ones in there at the moment might be stretched, meaning that the clutch engages too soon. This might be cheaper than a new clutch

 

[digitalsdc]

Thank you again for your responses. Last night I ordered a new Max-Torque 10T clutch, a new #40 chain, and a 60T sprocket. I also re-measured my rear tires and they're 15", not 16". Hopefully this will be a good combination to get us up and running and I can fine-tune the gearing with additional sprockets as I assess my son's driving.

I'll come back here and post the results whatever they are.