4 stroke engine runs, but won't engage when rev'd

[ONCBOY]

My 49cc 4 stroke Storm has been running fine, until recently. While cruising the neighborhood I noticed the engine would jump abit with a noticeble clank, too. Now, although the engine starts up and runs, the chain will not engage when the throttle is revved. I checked inside the gearbox to see if its chain was off track or broken, but not the case. I'd like to fix this rather than start from scratch with a new kit. Hopefully, this is a minor fix I can handle.

If need be, is there a reasonably cost better grade engine replacement out there to recommend or have any of you ever switched out your original setup with a cheaper 2 stroke? This is something I'm considering.

 

[ocscully]

I wonder if you have sheared one of the keys?, either on the output shaft of the motor?, or the output shaft of the primary reduction box?

ocscully

 

[MotorBicycleRacing]

How many miles do you have on it?

I thought the Storm kits used the infamous JL HOOT gearbox which have gears not a chain?

What gearbox do you have? A pic would help.
Does your motor have the centrifugal clutch built into the side
instead of a shaft?

Maybe the spring is broken on your centrifugal clutch or the shaft broke off the drum.

If it is the chain driven pocketbike gearbox then just run the bike with the cover removed
and the back wheel off the ground. It should be obvious what is broken.

My 49cc 4 stroke Storm has been running fine, until recently. While cruising the neighborhood I noticed the engine would jump abit with a noticeble clank, too. Now, although the engine starts up and runs, the chain will not engage when the throttle is revved. I checked inside the gearbox to see if its chain was off track or broken, but not the case. I'd like to fix this rather than start from scratch with a new kit. Hopefully, this is a minor fix I can handle.

If need be, is there a reasonably cost better grade engine replacement out there to recommend or have any of you ever switched out your original setup with a cheaper 2 stroke? This is something I'm considering.

 

[ONCBOY]

I took off the gearbox coverplate & the whole gearbox assembly and ran the engine both ways to see if I could troubleshoot the misconnection. Without the gearbox, their was no jumping or clanks from the engine & all was fine with accelarating the throttle. With the coverplate off & the chain from the gearbox to the tire sprocket reconnected, I found no clank but I did see that the gearbox chain wouldn't drive once the throttle was revved. I didn't see the purpose to further disassemble the engine past the gearbox and am assuming at this point it must be the culprit.

I'm not sure if the gearbox I have is a Hoot, but hopefully this is a simple replacement. If there are any other brands that are recommended (if that is all I need to fix this) that will fit this engine I'd love to hear them. I wonder if this is a common problem or if any of you have encountered such a dilemma. The engine itself runs well. I've only put about 30 miles of neighborhood riding on it and I'm hoping this replacement is all I need to get back on the saddle. Attached are some pics of my ride.

 

[Quenton Guenther]

Hi ONCBOY,

Looks like a "Hoot" chain drive to me. The clutch is mounted behind the front chain sprocket. When you rev the motor the cent. clutch is supposed to enguage, then spin the chain which is supposed to turn the output shaft via a freewheel.

Problems reported to us so far is the clutch spring has snapped and stopped the clutch from working. The clutch is attached to a tappered shaft a few have had the clutch spin on the tapper. Several have had issues with the freewheel [mounted as part of the larger chain sprocket], and it didn't enguage in either direction.

If the motor revs and the internal chain doesn't move, look into the cent. clutch [loose clutch or defective spring]. If the chain turns and the rear output doesn't turn, suspect the large freewheel assembly.

Have fun,

 

[ONCBOY]

What would be the recommended fix on this? Replace the Hoot?

 

[MotorBicycleRacing]

What would be the recommended fix on this? Replace the Hoot?

Remove your gearbox and see what is broken on your centrifigal clutch.
Just need to remove 4 bolts.
Probably just the spring...

If you want to replace it you could use the Grubee G4 gearbox.

Even if you upgrade the gearbox you will still need to repair the
clutch that is built into the motor.

 

[ONCBOY]

I am suspecting the freewheel. Then again, I learn as I go.

When I removed the gearbox assembly, I didn't notice any of the springs missing or broken from the centrifugal clutch. When I ran it without the gearbox -it ran well and appeared to expand when throttled (which I assume acts like brake drums by pressing outward for the connection of the hub to rotate the gearchain, etc.). The hub itself seems loose but is secured by its bolt. I'm guessing this is how it should operate, didn't wanna attempt tightening it any, just yet.

The freewheel bearing, covering the end of the gearshaft on the left, within the gearbox, spins freely but comes right off. The freewheel bearing on the right that's on the gearshaft end that drives the bike chain sprocket, is secured. I'm guessing this could be the whole problem.

Should this freewheel be secured and if so, how? Is there o-ring spring I'm overlooking that should hold it?

All help is appreciated, thanks again for your support and patience.

 

[Quenton Guenther]

Hi,

Best way to troubleshoot is to understand what might happen with drive system installed.

You should test with everything connected!

For example if the sytem is disconnected and you simply watch the clutch you don't really know what is taking place under load.

I am attaching a picture of a Blown crankshaft which was connected to the clutch in a hoot chain drive system. The clutch is attached to the crankshaft via a taper fit. The taper fit doesn't use a key and without a load could appear to work. If the clutch is slipping on the tapered shaft it might look as it works without a load, but under load the crankshaft could spin inside the clutch taper.

If the chain spins with the motor running and the rear wheel doesn't move then suspect the freewheel or snapped keys. If the chain doesn't spin with everything connected then it is the clutch system.

We have had a lot of calls about the "Hoot" drives, and it looks like they still have a lot of problems. The chain drive version was to be better than the gear drive versions, however the single chain versions jump the sprockets when the chain stretches [don't tell anyone, but Chinese chains won't win any quality awards] and usually rip the teeth off the drive sprocket. The fix was to use a double chain [don't tell anyone, but Chinese double chains won't win any quality awards either] on the next version, but as the chain stretched it also jumped the sprockets, but usually hits the case with a warning of problems to come.

Have fun,

 

[ONCBOY]

I ran it, closer inspected things and from what I've detected (without taking the whole engine apart) is what I think is called the clutchbell (pictured). Pardon my ignorance, I learn as I go -not a mechanic.
My clutchbell's bolt nut is tight, but the gap between the nut and the bell allows it to spin freely & a bit wobbly. With the gearbox in hand, I manually tried spinning it just to see if it would connect the gearbox chaindrive, it won't. Just spins. Is there a type of o-ring spring that should be behind that nut, I'm not seeing it. What I do see is a little wear on the bell, behind that nut, that would make me think this is all I need.
If so, are there any sites recommended for this part (if there is one)? Is this common? Am I totally off the mark? Any help offered is gladly appreciated.
Thanks.

 

[Tad Bit Tipsy]

That's definitely a clutchbell problem. Any washer would do, but try and tighten it down some more, if it won't, use a washer of good quality. That should solve the problem. You have to realize they spit out these chain drives like crazy, so the build quality is not the best on every one, you get some bad eggs. But they are salvageable and can be quite easy to maintain. While you got it down, check the chains. I replaced mine with Heavy Duty ones from this electric scooter store, so far no problems with stretching.
Electric Scooter Chain - ElectricScooterParts.com
They are the #25 chains. Good Luck.

Worst case scenario, they are cheap to replace, Dax has them for $40.

 

[MotorBicycleRacing]

Remove the nut and see why the clutch drum is not being turned
by the shaft.........

If you have broken parts it may be cheaper to upgrade to a new gearbox
and I doubt if anyone carries parts.

This gearbox will fit your motor.

only $34.95 with shipping already included !!!

Gas Scooter Mini Moto Bike Parts Transmission Moped: eBay Motors (item 180360796487 end time Sep-16-10 01:06:19 PDT)

A higher quality choice for that motor would be the Grubee G4 gearbox for $120?

I ran it, closer inspected things and from what I've detected (without taking the whole engine apart) is what I think is called the clutchbell (pictured). Pardon my ignorance, I learn as I go -not a mechanic.
My clutchbell's bolt nut is tight, but the gap between the nut and the bell allows it to spin freely & a bit wobbly. With the gearbox in hand, I manually tried spinning it just to see if it would connect the gearbox chaindrive, it won't. Just spins. Is there a type of o-ring spring that should be behind that nut, I'm not seeing it. What I do see is a little wear on the bell, behind that nut, that would make me think this is all I need.
If so, are there any sites recommended for this part (if there is one)? Is this common? Am I totally off the mark? Any help offered is gladly appreciated.
Thanks.