Go kart clutch/engine help

[lewikenzie1]

Helloo all, first time posting

I have a 13hp(gx390 clone) and have just mounted it on my go kart to find out that the centrifugal clutch i bought is useless(its ment for upto 13hp engines but when trying to pull away it just smokes then aventually works) so im wondering what to do, i want about 50mph out of it and acceleration needs to be quite good. What should i use : a different centrifugal clutch, a torque convetor or an actual clutch or is there something else?
Im in the UK
Thanks in advance

 

[Russ2251]

Ratio and tire diameter?

 

[lewikenzie1]

thanks for the quick reply right now the clutch is 10 or 12 tooth, the back wheel diameter is 45cm and the axle sprocket is 52 or 55 tooth

 

[anderkart]

You really should count those teeth so we can give you better advice.
Also, will you be leaving your engines governor all hooked up?
And finally what brand/model clutch do you have?

 

[redsox985]

With tires that large and a cent. clutch, you will need a steep ratio (8:1 or so) as not to smoke it. To achieve the acceleration, you will also need a low ratio. To achieve 50 MPH, you will need a very high ratio (say 3:1) which will smoke your clutch in no time flat. The only way I would say you could do this would be with a snowmobile, street bike, or quad/dirtbike style engine which would have a gearbox (quad/bikes) or a large CVT and both will boast higher RPMs than the GX. A street bike, quad/dirtbike, or snowmobile engine will allow for both good acceleration and top speed, unlike a GX with cent. clutch.

 

[Doc Sprocket]

I have to agree with the above. Your tires work out to about 16 1/2". I can give you personal experience here. I have a GX340 11hp, with tires that measure 17 1/2". I have a Comet 40 CVT, and a fairly heavy kart. I am geared with 4.8:1 final ratio, and I top out at 45MPH, with a decent stretch of road. When I was geared higher (4:1) my top speed was actually LOWER due to HP limitations, and I know I was pushing my luck. Gearing down made my belt last longer and my top speed improve a bit.

So you can get a CVT and safely expect 40, maybe 45 MPH (My engine maxes at about 4200 RPM), or you can get one of the above-suggested engine/tranny combos.

You WON'T get 50MPH with a centrifugal clutch combined with everything else you have.

 

[anderkart]

Man you guys sure aren't very optimistic today

My 10hp flathead Honda ran 50 with a Centrifugal, and still had fairly decent acceleration. I just had to use a $150 clutch and get my engine to spin up to 5000rpm.

You guys just dont realise how much better a 1" race clutch is compared to those bargain-bin 3/4" models. Quite a few guys over on the heymow forum run my same 1" Star clutch model with 40/50hp engines, and report they've been holding up great.

As long as the OP and his kart aren't super heavy, I think 50 is doable even with his tall tires. Those GX390-clones have a lot more torque than a 6.5. They can pull a higher ratio and still wind out.

With a:
13T clutch (I recommend using a Noram Star clutch, smallest driver size available is 13T)
68T axle sprocket
17.7" tires
As long as you could get that engine spinning at 5000rpm = 50mph.

To do this you'd probably just have to remove the governor, install a good race header/air cleaner and re-jet the carb. But If that wouldnt wind out to 5000rpm, there's all kinds of speed parts available for your engine that would make it pull strong up to 6500rpm.

 

[Doc Sprocket]

Okay- you're right. BUT I was working with him having a stock engine...

 

[redsox985]

I could find a dirtbike engine with gearbox and rev limiter ~9,000 RPM for the cost of that clutch, not to mention if the GX was sold too.

 

[lewikenzie1]

Cheers for the help guys what do you mean by the governor (I'm 14 btw) and I've had the engine at about 9700 rpm

 

[lewikenzie1]

Btw engine is a stock (kinda tuned) gx390 clone

 

[Russ2251]

and I've had the engine at about 9700 rpm

How did you accomplish this? What tach was used to determine this reading?

 

[lewikenzie1]

How did I measure it? My dads mate owns an engineering firm and hooked up the shaft to a machine then started it and left it for a couple of mins then revved it up full and it got about 9700 rpm

 

[Russ2251]

9700 rpm is extremely high. What mods have been done?

 

[Doc Sprocket]

Hold on. A "stock, (kinda tuned)" gx390 clone spinning just shy of 10k?
I really would like to know what has been done to this engine.
You all will forgive me if I'm a wee bit skeptical about this one.

 

[Russ2251]

I'm a wee bit skeptical about this one.

I have another word for it...

 

[redsox985]

There would be nothing "kinda tuned" about getting a GX up to 9700RPM. I have a feeling that it should be more like 3700. If you don't even know what a governor is, this thing isn't hitting 9700RPM.

Have you ever opened up the block and done any work on the motor's guts? What mods have you done to it?

 

[Russ2251]

Tach was set wrong.

 

[lewikenzie1]

There would be nothing "kinda tuned" about getting a GX up to 9700RPM. I have a feeling that it should be more like 3700. If you don't even know what a governor is, this thing isn't hitting 9700RPM.

Have you ever opened up the block and done any work on the motor's guts? What mods have you done to it?

Yes the air intake has been modded to take a bit more air in, apart from that the idle speed is the only other thing that iv changed.


Btw thanks for the help guys you's are helpful and quick at responding


EDIT: it gets to 2100 rpm with a tap on the throttle so does that mean itshighly tuned, and I'm only 14 what does the governor do is it like a limiter?

 

[lewikenzie1]

Good news ppl found a honda superdream 400 comes with clutch and gearbox all for £100