New and already need help

LickOliver · Sep 22, 2024

Hi my name is Chris, I just got back my 80cc gas powered bike. It ran fine when I last had it but sat for a year. I drained the tank, replaced fuel lines and filter. Lubed chains and cables, as well as checked the spark plug. It fires up fine and runs but there's a knocking in the engine and after a few moments of riding the chain wants to temporarily seize up. Any help would be greatly appreciated as this is my first and I want to get knowledgeable and capable of repairing it. It's my main means of transportation rn in the small town I live in. Thank you in advance for letting me join and any and all assistance to making this a dependable build.

Captain Awesome · Sep 22, 2024

Knocking in the engine - never good
“Seizes” up once warm/hot - usually not good

Start with the simple things. Does it have oil in it? Not being condescending just wondering

Oils supply? Bad bearing?

LickOliver · Sep 23, 2024

Captain Awesome said:
Knocking in the engine - never good
“Seizes” up once warm/hot - usually not good

Start with the simple things. Does it have oil in it? Not being condescending just wondering

Oils supply? Bad bearing?

It runs on mix and I can't find any where to add oil or a reserve. Under a friends suggestion I've been running it at a 50:1 ratio. I get its not good, just not sure how the issues might be related and how to diagnosis and fix it. The chain was loose but I fixed the tension and the issue is continuing. Almost like the issue is a spot in the chain but visually I see nothing out of whack. I'm beginning to think I need to take apart the chain connection at the engine to get a look but have hesitated due to lack of experience with them.

Just brought it to my shop at work, now that it's been sitting the clutch engaged just fine and the chain moves freely. That said it also while running seems to want to consistently accelerate and won't idle. My boss who has experience with general 2 stroke engines suggested due to the idle it could be a clutch issue. Thoughts of where to start from here? I attached a couple pictures, where the clutch is connected to the motor I noticed what looks like trufuel but no odor and thicker coming out a little bit at the nut on the clutch cable connection, if that helps. Plus the very bottom of the case for the gears shown the screw cover hole at the bottom has a small amount of oil around it. Is there a way or need for oil, that'd make sense to me cause the gears there are dry and there's a gasket around it?

twojs.bike · Sep 23, 2024

I struggled with small 2 cycle engines for years. Leaf blowers, string trimmers, etc. I was lucky to get a full season out of them without major headaches. Finally, about 10-12 years ago, I bought all new equipment and started running them on the pre-mixed fuel from the hardware store. Non-ethanol. I have been running the same equipment ever since. Zero problems, zero maintenance. Sure the pre-mixed stuff is expensive, but I use so little it doesn’t add up to more than $20 a year or so. Once you get this thing running, my advice would be to buy the pre-mixed fuel.

LickOliver · Sep 23, 2024

twojs.bike said:
I struggled with small 2 cycle engines for years. Leaf blowers, string trimmers, etc. I was lucky to get a full season out of them without major headaches. Finally, about 10-12 years ago, I bought all new equipment and started running them on the pre-mixed fuel from the hardware store. Non-ethanol. I have been running the same equipment ever since. Zero problems, zero maintenance. Sure the pre-mixed stuff is expensive, but I use so little it doesn’t add up to more than $20 a year or so. Once you get this thing running, my advice would be to buy the pre-mixed fuel.

Appreciate I actually am using the trufuel pre mix at the 50:1 ratio. Especially after I drained the tank from sitting and replaced the fuel lines and filter.

ifitsfreeitsforme · Sep 23, 2024

those Chinese two strokes are not easy to work on. They can be finicky. I used to race pocket bikes with similar engines. I hope you figure out the problem. Wish I had a suggestion for you.

Captain Awesome · Sep 23, 2024

I don’t know anything about those specific Chinese bicycle engines, but I do know two strokes front to back. Do those things not have any lower end lubrication? They don’t have gearbox oil (even though I know it doesn’t have a gearbox)

The way you described the problem as running for a while and then almost seizing up I guess is where I have questions. Does it seem like when it gets hot it just slowly comes to a stop or does it just shut off and stop running altogether? I’m thinking the tolerances in these things can’t be, great

If you take the drive chain off, will the motor just run on its own? Be interested to see if without the load on it and revs just fine and continues to do so.

LickOliver · Sep 23, 2024

Captain Awesome said:
I don’t know anything about those specific Chinese bicycle engines, but I do know two strokes front to back. Do those things not have any lower end lubrication? They don’t have gearbox oil (even though I know it doesn’t have a gearbox)

The way you described the problem as running for a while and then almost seizing up I guess is where I have questions. Does it seem like when it gets hot it just slowly comes to a stop or does it just shut off and stop running altogether? I’m thinking the tolerances in these things can’t be, great

If you take the drive chain off, will the motor just run on its own? Be interested to see if without the load on it and revs just fine and continues to do so.

It fires up and runs but seems to want to slowly continuously accelerate and within moments there's a knocking but not regular enough to be the chain. The knocking is there when not running but peddling and as sun as you cut it off the chain Seizes. It is also backfiring some.

Captain Awesome said:
I don’t know anything about those specific Chinese bicycle engines, but I do know two strokes front to back. Do those things not have any lower end lubrication? They don’t have gearbox oil (even though I know it doesn’t have a gearbox)

The way you described the problem as running for a while and then almost seizing up I guess is where I have questions. Does it seem like when it gets hot it just slowly comes to a stop or does it just shut off and stop running altogether? I’m thinking the tolerances in these things can’t be, great

If you take the drive chain off, will the motor just run on its own? Be interested to see if without the load on it and revs just fine and continues to do so.

Best way I can describe it is after sitting it peddles and fires with no issue but in just a moment of running develops a knocking and when cut off the chain seizes. The knocking remains present after it's cut off and by feeling with my hand it doesn't seem to be where the piston is. It's also backfiring. When running it slowly continues to accelerate. I greased the gears shown above but it's persisting.

ifitsfreeitsforme · Sep 23, 2024

continuing to accelerate is called "a runaway". That can only be caused by one thing, an open throttle or air leak. It has to be getting more air somewhere and that's the only way it will rev higher.

Captain Awesome · Sep 23, 2024

ifitsfreeitsforme said:
continuing to accelerate is called "a runaway". That can only be caused by one thing, an open throttle or air leak. It has to be getting more air somewhere and that's the only way it will rev higher.

I’m assuming these have some type of a crank seal in them as well. Which kind of ties in with this knocking if it has a bad or loose bearing and therefore also may be a crank seal it’s going to draw any air canon through that gap

ifitsfreeitsforme · Sep 23, 2024

Not sure my memory is correct here, but in the 80s I had a two stroke Honda moped with bad crank bearing seals and it would not run. I don't think air drawn in there would mix with fuel to run, and without a vacuum in the crank area, it won't draw the fuel/air mixture? Correct me if I'm wrong. But still, if he has enough of a seal, his knocking sound could be bad bearings so that's a good idea.

How about the centrifugal clutch? He may have broken a spring.

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