Clutch problems on 4 stroke 49cc engine kit

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DanielMaia

New Member
Jun 24, 2009
309
0
0
Portugal
Hi there guys,

Im having some problems on a 4 stroke engine kit.

The first problem was burn completely the clutch, after 5 miles of use.

It uses a 11T front sprocket. I thought it was because the 40T sprocket, changed for 44T sprocket, bought a new clutch kit on a local store, went for a ride, and it seems the clutch is spinning a lot..in a little hill, even with max throttle, the clutch doesnt "stick" on at all..

Im not heavy (around 150 pounds), the bicycle has about 60 pounds...

I was thinking in the carburetor...if the carb is not tuned properly, it may not accelerate as it should, and the clutch springs does not expand..

What you guys think?
 

GasX

New Member
Oct 7, 2011
277
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0
Florida
You should be able to tell if the engine is revving up by the noise. If the revs increase and nothing engages, then it's the clutch.
 

DanielMaia

New Member
Jun 24, 2009
309
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0
Portugal
At no load (on stand) it is revving good. It revs until it reaches a mid rpm (up hill) but down a hill it does 60km/h..at striaght road, does 45km/h
 

Fugi93

New Member
Dec 30, 2011
144
0
0
illinois
Hi there guys,

Im having some problems on a 4 stroke engine kit.

The first problem was burn completely the clutch, after 5 miles of use.

It uses a 11T front sprocket. I thought it was because the 40T sprocket, changed for 44T sprocket, bought a new clutch kit on a local store, went for a ride, and it seems the clutch is spinning a lot..in a little hill, even with max throttle, the clutch doesnt "stick" on at all..

Im not heavy (around 150 pounds), the bicycle has about 60 pounds...

I was thinking in the carburetor...if the carb is not tuned properly, it may not accelerate as it should, and the clutch springs does not expand..

What you guys think?
What kind of gearbox do you have?
 

ocho ninja

Member
Jan 14, 2012
564
2
16
San Jose, CA
Those gear boxes only have a 3:1 reduction I believe.

So it needs a rear sprocket that has something like 50t to get good reduction for it to accelerate properly
 

DanielMaia

New Member
Jun 24, 2009
309
0
0
Portugal
Yes it is. 9 tooth sprocket just after the centrifugal clutch, 27T on big wheel; 11T front sprocket, 44T on the wheel
 

DanielMaia

New Member
Jun 24, 2009
309
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0
Portugal
thank you guys,

i will also do some sanding on the clutch drum, it is completely sleek and polished, and may not be good to attach on the clutch pad
 

GasX

New Member
Oct 7, 2011
277
0
0
Florida
That picture is not the Dax gear box. That one has a freewheel sprocket which fails VERY quickly. Mine lasted 50 yards into my maiden voyage The dax gear box, which I now have, has a fixed sprocket. I ran mine with a 44 tooth rear sprocket just fine, but switched to a 56T for the ability to start from a near dead stop. Top speed is about 32-35mph.
 

The_Aleman

Active Member
Jul 31, 2008
2,653
4
38
el People's Republik de Kalifornistan
OP should definitely redo the gearing. 9->27, 11->44 is a 12:1 overall ratio, which works out to about 13MPH at engine idle with 26" wheel. No take-off power.

Should work on getting at least 15:1 or better. I have a 3-speed setup with a similar engine and my 3rd gear is about 15:1. That is still too tall off the line.

A 56T on rear wheel would get you about 15.27:1. With a 26" wheel that is 35-36MPH @ 7000RPM, your horsepower peak.
That is the tallest ratio I would recommend with your engine, as with 2HP, that's about as fast as you'll be able to go, anyway - without any wind.
If you want better off the line power, you'll need to move closer to 18:1 - a 66T. With a 66T, idle is 8.6MPH and HP peak comes at 30MPH.

That little bit makes a big difference in lower-speed capability. Shorten that ratio up or think about gears lol :D
 

locutus_1

New Member
Oct 31, 2010
196
0
0
california
here is what you need to do.. the stock clutches are made for running water pumps and things like small generators when you put a 200 lbs man on the stock clutch springs will not fully engage the outter ring this is on purpose ... what you need to do is get a spring thats half the tension.. and bend it to the stock spring.. my clutch fully engaged just after throttle..... next you need to take apart your clutch there is 3 bolts where the springs are sometimes from the factory they dont lube tbe bolts that the shoes ride on

so pull these out and scuff them up with 100 grit sand paper.. then wipe them off a dab and i say dab of green bearing grease aka high temp on your finger and super thing layer of grease other wise it will fling off onto the shoes and slip.. after you lubed them put it back togehther

thake your sand paper and scuff up the pads scuff up the clutch bell where they ride.. then use gas or carb cleaner and clean off the shoes and bell.. then reasemble with your new springs etc..

i got my springs from home depot trial and error to light and its always engaged to strpong and it wont engage you might have to make multiple trips its a pain to bend them in the right position

after its all done you will have a clutch that engages just after 1.4 throttle or 2500 rpm.. and bring your rpm down to 1500 -2000 other wise it will be partially engaged and burn out..

hope that helps..

and oh thread lock on every part of your bike from your fenders to handlebars.. will save you falling off from a bolt