First time working on a motorized bike, confused about some things. Possibly complex.

LeviNewBikeBoy

New Member
Joined
May 17, 2022
Messages
4
Hi, recently i found a rusted out Raleigh mountain bike with a 49 cc 2 stroke kit attached and an nt carb. It was pretty badly maintained, maybe a little shoddily put together and it looked like it hadn't run in a while. Motor dated 2007.

I did a bunch of research on here and elsewhere before starting the to work on it. I cleaned and reassembled the carburetor, replaced the kill switch, i removed the rust from the tank and resealed it, put in a new throttle grip and cable, fitted new brakes and new tubes. It was also missing any air filter so i used a couple layers of steel window screen for now.

I finally got it to start the other day and it was seemingly running well but the clutch wouldn't disengage at speed. The kill switch wouldn't work, so i was only able to stop the engine with the brakes. Not so safe. I went in and tried to adjust the clutch this morning, but now the engine is dying when the clutch is released.

The engines seems to take longer to die at high revs and when the engine is hot. It never lasts more then a few seconds with the clutch released. Another issue, if i tighten my low idle screw up then the idle sounds healthier, but sometimes the bike will seemingly rev much higher with the clutch disengaged, and then accelerate with the clutch engaged, even without throttle. This isn't consistent, but occasional. Pretty scary, i had to use the kill switch.

Also the idles sounds very weak when the bike starts, especially cold. It sounds much healthier at mid to mid high revs. Also, i seem to have the strongest acceleration at 70-80% throttle, but the engine bogs considerably if i go beyond that. Anyway, I know there's a lot going on here but i'm a new guy coming over from ebikes, if anyone has any ideas or next steps id appreciate it.
 

Zak

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Joined
Mar 21, 2019
Messages
1,185
Welcome. Good luck. I'm no expert but you.may have a leak in the intake. Make sure your o-ring is in the carb/intake manifold joint. You can use carb cleaner/propane/starting fluid to check for leaks also. Also see if you might have a leak around the crank seals by the magneto or on the other side. Lunch is over, gotta go.
 

weefek

Active Member
Joined
May 14, 2022
Messages
385
Sounds like the throttle cable / carb cyl could have a sticky spot -- some cables even brand new have sticky spots and need to be lubricated properly. Probably not your issue but should be done regardless.

Check head nuts for proper torque.

There is a lot of good info on this forum if you spend a little while looking around for it and looking at the 'similar threads' section at the bottom of every page.

Might not be a bad idea to take the head / jug off and inspect the piston rings. Change the spark plug.

Did you get the kill switch working?
 

LeviNewBikeBoy

New Member
Joined
May 17, 2022
Messages
4
Thanks for the reply. Yes, the kill switch is working thankfully. I didn't think about the throttle cable sticking, i haven't lubricated it at all. I haven't had the head off yet, i was hesitant to get into the engine itself. I bought a plug but it had the wrong end for my cdi. Another is on the way. What do you mean by carb cyl? How would i correct it? I'm brand new.
 

weefek

Active Member
Joined
May 14, 2022
Messages
385
Not 100% sure what the proper term is (throttle valve?) but it's the cylinder that the throttle cable is attached to, the spring from the cap pushes against it and the needle comes out the bottom. I would just verify that it smoothly opens and closes as you pull and let go of the throttle. Something easy and quick to check.

Pulling the head off is also easy and a quick thing to check the cylinder bore for abnormal scoring / wear / etc. Just make sure you have a torque wrench when you go to reinstall it. If it has acorn nuts, throw those away and get proper nuts with washers and lock washers. From what I've read about 10 ft lbs of torque on the 49cc heads , 12 would probably be better. Check the gasket which should be copper while you're at it. Always torque heads in an X pattern

1 2
3 4

torque in order 1, 4, 2, 3 OR 1, 4, 3, 2 (doesn't matter as long as it's X)
 

Chainlube

Well-Known Member
Joined
Jan 5, 2020
Messages
6,251
Not 100% sure what the proper term is (throttle valve?) but it's the cylinder that the throttle cable is attached to, the spring from the cap pushes against it and the needle comes out the bottom. I would just verify that it smoothly opens and closes as you pull and let go of the throttle. Something easy and quick to check.

Pulling the head off is also easy and a quick thing to check the cylinder bore for abnormal scoring / wear / etc. Just make sure you have a torque wrench when you go to reinstall it. If it has acorn nuts, throw those away and get proper nuts with washers and lock washers. From what I've read about 10 ft lbs of torque on the 49cc heads , 12 would probably be better. Check the gasket which should be copper while you're at it. Always torque heads in an X pattern

1 2
3 4

torque in order 1, 4, 2, 3 OR 1, 4, 3, 2 (doesn't matter as long as it's X)
It's called a slide.
 

Daytripper24699

New Member
Joined
Apr 19, 2022
Messages
14
Thanks for the reply. Yes, the kill switch is working thankfully. I didn't think about the throttle cable sticking, i haven't lubricated it at all. I haven't had the head off yet, i was hesitant to get into the engine itself. I bought a plug but it had the wrong end for my cdi. Another is on the way. What do you mean by carb cyl? How would i correct it? I'm brand new.
Your plug is probably fine... some of these cdi require us to unscrew the top off of plug to be used.
 
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