My first motorized bike, few issues so far

Datboi

New Member
Nov 12, 2020
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0
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I've build my first motorized bicycle. I put a 80cc Chinese engine on a mountain bike with no suspensions.

I mostly use it for mountain biking in the hills and off road, so I give the engine quite a beating. Especally the clutch.


I have a few issues, first of all, what are the pros and cons of running a richer gas-oil mixture, I'm currently running 65ml of oil to 1l of gas as I'm breaking the engine in. What would happen if I always run the engine at that ratio even after break in? Can someone give me a run down of pros and cons?



Let's start with the issues I'm having
4 stroking at full throttle (the engine starts 4 stroking when I stay at full throttle for a bit and the engine starts revving high)

Whenever I'm going at low to moderate speed, the engine 4 strokes at low to mid throttle. If I open up the throttle completely it doesn't 4 stroke until it revs really high


The issue is, I've done a plug chop, the spark plug has slightly tan and looks perfect, If I move the clip on the leanest position I'm scared I'll be running the engine too rich! I tested it at full throttle and mid throttle. What should I do?


2nd issue: low power, possibly low compression or bad clutch.

I have issues going up hills, the engine just doesn't have the power, I feel like there is a compression issue, the gasket on the cylinder is a joke, I feel like this engines lose a lot of compression due to those bad seals. How can I test if I have compression without a compression gauge? The engine does have quite a bit of resistente so idk!


3rd issue: very very loud clutch noises at full throttle.

Whenever I gain some speed, the clutch makes a TERRIBILY loud screeching noise, the more speed I pick up at full throttle, the louder the noise, its louder than the engine itself! The noise is that of a very old metal door opening.

I've put f*** ton of grease on the clutch gears on the right side of the engine. But that didn't fix it.

Im not 100 %sure it's the clutch making the noises. But it only happens when the clutch in engaged, at low speeds there is little to no noise, but the more I pick up speed the more noise!


Could it be that the clutch is slipping at high rpm? The adjustor nut is as tight as I can make it while still being able to turn the real wheel with the clutch pulled in.


Also the clutch doesn't seem very good, whenever I'm going up a hill or from a dead stop it's defently not as grabby as I would like it to be! However it might just be that I expect too much from this clutch? Any tips? Thanks guys
 

Greg58

Well-Known Member
May 1, 2011
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Newnan,Georgia U.S.A.
The clutch is fairly basic, it's not designed to be used from a dead stop. You should always pedal first then release the clutch. Slipping the clutch regularly will wear out the pads quickly. As for the power make sure the head is true, use fine sandpaper on a true flat surface to sand the sealing surface to remove all high spots, then torque the nuts to 12 foot pounds. Be sure to use a torque wrench, you can over tighten and warp the head. Fuel mixture is often debated, I start at 24/1 then after a couple of tanks I use 32/1.
 

kaneto

Member
Jun 6, 2016
34
1
8
Bulgaria
I've build my first motorized bicycle. I put a 80cc Chinese engine on a mountain bike with no suspensions.

I mostly use it for mountain biking in the hills and off road, so I give the engine quite a beating. Especally the clutch.


I have a few issues, first of all, what are the pros and cons of running a richer gas-oil mixture, I'm currently running 65ml of oil to 1l of gas as I'm breaking the engine in. What would happen if I always run the engine at that ratio even after break in? Can someone give me a run down of pros and cons?



Let's start with the issues I'm having
4 stroking at full throttle (the engine starts 4 stroking when I stay at full throttle for a bit and the engine starts revving high)

Whenever I'm going at low to moderate speed, the engine 4 strokes at low to mid throttle. If I open up the throttle completely it doesn't 4 stroke until it revs really high


The issue is, I've done a plug chop, the spark plug has slightly tan and looks perfect, If I move the clip on the leanest position I'm scared I'll be running the engine too rich! I tested it at full throttle and mid throttle. What should I do?


2nd issue: low power, possibly low compression or bad clutch.

I have issues going up hills, the engine just doesn't have the power, I feel like there is a compression issue, the gasket on the cylinder is a joke, I feel like this engines lose a lot of compression due to those bad seals. How can I test if I have compression without a compression gauge? The engine does have quite a bit of resistente so idk!


3rd issue: very very loud clutch noises at full throttle.

Whenever I gain some speed, the clutch makes a TERRIBILY loud screeching noise, the more speed I pick up at full throttle, the louder the noise, its louder than the engine itself! The noise is that of a very old metal door opening.

I've put f*** ton of grease on the clutch gears on the right side of the engine. But that didn't fix it.

Im not 100 %sure it's the clutch making the noises. But it only happens when the clutch in engaged, at low speeds there is little to no noise, but the more I pick up speed the more noise!


Could it be that the clutch is slipping at high rpm? The adjustor nut is as tight as I can make it while still being able to turn the real wheel with the clutch pulled in.


Also the clutch doesn't seem very good, whenever I'm going up a hill or from a dead stop it's defently not as grabby as I would like it to be! However it might just be that I expect too much from this clutch? Any tips? Thanks guys
Make sure the clutch cable is not too taut and that there is no grease on the pads.
 
Last edited:

JerryAssburger

Active Member
Mar 11, 2017
205
114
43
Salem Oregon
On my China-Girl, it was the two gears inside the case. You could actually see the larger one wobble a bit. They were noisy as heck. Some marine-grease quieted them down a bit, and as I rode it more, it was getting quieter.

I think until the engine is fully broken in, I wouldn't sweat tweaking it. I think most people are saying you need to run about 4 tanks of gas through it before it even starts to run as well as it can.

I had a pretty bad time with my compression also until I swapped both the head gasket AND the head for a new stock head. You could hear it hissing and could see a smear of oil forming between the head and cylinder. Also, an almost DAILY ritual is checking the torque on your head-bolts.


I would say, if you're doing mostly low-speed riding (under 20 mph), you might benefit from a larger rear sprocket. You will lose top-speed ability but it sounds like you're more into it for the hills and trails, so you might not want to be doing over 20.

Either way, good luck and don't give up. My China Girl taught me to be patient, and it seemed to run better and better the more I rode it.
 

carburetor al

New Member
Jun 14, 2020
15
11
3
73
On my China-Girl, it was the two gears inside the case. You could actually see the larger one wobble a bit. They were noisy as heck. Some marine-grease quieted them down a bit, and as I rode it more, it was getting quieter.

I think until the engine is fully broken in, I wouldn't sweat tweaking it. I think most people are saying you need to run about 4 tanks of gas through it before it even starts to run as well as it can.

I had a pretty bad time with my compression also until I swapped both the head gasket AND the head for a new stock head. You could hear it hissing and could see a smear of oil forming between the head and cylinder. Also, an almost DAILY ritual is checking the torque on your head-bolts.


I would say, if you're doing mostly low-speed riding (under 20 mph), you might benefit from a larger rear sprocket. You will lose top-speed ability but it sounds like you're more into it for the hills and trails, so you might not want to be doing over 20.

Either way, good luck and don't give up. My China Girl taught me to be patient, and it seemed to run better and better the more I rode it.
I am not the biggest expert on motor bicycles. I do know about clutches Anyway ,remove the clutch cover. Try cleaning the clutch pads with a decent automotive cleaner. I would not use carb or brake cleaner as they may deteriorate the clutch pads , Do not remove them. Do clean them in place .Let the pads dry over night .In my experience, turning the center nut in just a single position after removing the screw that keeps it from backing out will give you a decent clutch response. Put the little screw back in and ride the bike .If it feels good ,put the cover back on and you are through. If not, is the clutch now dragging (not releasing all the way).If so turn the center nut back out .If it is better ,but not quite where you want it ,try turning it inward another click. This does not mean a full or turn of the center nut. It is easier to get desired results , when you make these small adjustments .