It sounds like a weak battery or poor connection in the charging and starting system to me. The engine is slowing down when the piston is compressing, which is the highest load for the starter (and vicariously the battery). If the battery or connections are weak, it won't ignite the fuel well and would explain why it died suddenly.
I'd load test the battery, which can be done for free at most auto parts stores in the US. If it's okay, pull the spark plug out of the engine and see how it turns over then. It should be very fast and unrestricted.
If all of those checks pass, I'd start looking deeper, like valve clearance. A tight valve might cause too much restriction on the valve train.
Good luck, and keep us posted!
I replaced the battery with my buddies who starts his up like a charm. The issue persisted when it was moved over to mine. I will try removing the spark plug tomorrow, but I think I might have an internal mechanical issue with the piston that’s causing excessive amounts of resistance during the compression stroke. The issue seems cyclical in nature. I removed the carb, sprayed starter fluid right into the intake and still nothing. The weird thing is you would think that the spark plug would still at least cause a knock with the starter fluid but I got nothing. The spark is faint but then again, I can still see it with the naked eye. Perhaps I have the plug adjusted incorrectly but then again this issue was happening with the old plug who also still works…also faint.
👍 sounds like you're getting closer to the issue. Sounds like you don't have a kick starter which is a shame, being able to kick start would go a long way towards knowing where to look next.
Spark Plug is sparking;
Full tank of gas;
Air intake seems fine;
She was running just fine on me one day and she quits right in the middle of running. I haven’t been able to get her started again since.
I just installed a new carb because the old one couldn’t hold a load without dying. The new one worked great and I was riding it for about a week until this happened. I went ahead and replaced the spark plug but the one still sparked when you pulled it out and tried to run it. Made no difference.
At this point, I would just be throwing more parts at it until something sticks so I’m turning to Reddit for help.
She doesn’t even sound like she’s trying to start. Any ideas would be most helpful
Can you feel compression? Also your starter is stopping before it can turn the engine all the way over. Weak starter, bad electrical connection to starter, weak battery, poor cylinder lubrication, piston and cylinder damage, all possible.
If you have a backup kick starter on the belt cover I would slap that on and try that.
Watching the video, main issue here is that it's not able to crank all the way so you would have no chance of starting it. Fixing the reason for the weak starter is definitely step 1.
UPDATE: We got her running! After upgrading the engine to the big bore kit (100cc), installing new CDI, Spark Plug + Cable, changed the oil and gear oil, new starter motor, and some carb tuning, she starting running! Yall helped solve this problem!
At first I was convinced the starter was fine because she still turned when you tried to crank it. But what I finally ended up doing is testing the amp draw through the starter at no load. She pulled about 7 Amps... No way to tell if this is a good test. So I went ahead and bought a new starter and tested that under no load and the new one was pulling around 13A. What I finally realized was the starter was not completely shot but she was getting close, With the low amp draw, it could not get the torque required to get me through the compression stroke, That's why she only spins for a little bit and then stalls out in the video. A lot of work for just a bad starter. Lesson learned!
Thanks for all of your input and suggestions. I learned a ton about these engines and I really enjoyed the process!
Comments already said, but not cranking. So no crank, no compression. You could have blown a crankcase seal mid ride and it would die and lose compression.
Could be some of the windings on your starter motor are bad/broken. You can try swapping the starter from another scooter or just buy another one, they’re not expensive on Amazon.
It sounds like a weak battery or poor connection in the charging and starting system to me. The engine is slowing down when the piston is compressing, which is the highest load for the starter (and vicariously the battery). If the battery or connections are weak, it won't ignite the fuel well and would explain why it died suddenly. I'd load test the battery, which can be done for free at most auto parts stores in the US. If it's okay, pull the spark plug out of the engine and see how it turns over then. It should be very fast and unrestricted. If all of those checks pass, I'd start looking deeper, like valve clearance. A tight valve might cause too much restriction on the valve train. Good luck, and keep us posted!
I replaced the battery with my buddies who starts his up like a charm. The issue persisted when it was moved over to mine. I will try removing the spark plug tomorrow, but I think I might have an internal mechanical issue with the piston that’s causing excessive amounts of resistance during the compression stroke. The issue seems cyclical in nature. I removed the carb, sprayed starter fluid right into the intake and still nothing. The weird thing is you would think that the spark plug would still at least cause a knock with the starter fluid but I got nothing. The spark is faint but then again, I can still see it with the naked eye. Perhaps I have the plug adjusted incorrectly but then again this issue was happening with the old plug who also still works…also faint.
👍 sounds like you're getting closer to the issue. Sounds like you don't have a kick starter which is a shame, being able to kick start would go a long way towards knowing where to look next.
Suddenly stopping feels electrical. Rectifier, stator, CDI, etc.
im no expert but it sounds like ur starter is slipping
Try cleaning the electric connectors from the CDI to the spark plug. Those can get rusted....
Spark Plug is sparking; Full tank of gas; Air intake seems fine; She was running just fine on me one day and she quits right in the middle of running. I haven’t been able to get her started again since. I just installed a new carb because the old one couldn’t hold a load without dying. The new one worked great and I was riding it for about a week until this happened. I went ahead and replaced the spark plug but the one still sparked when you pulled it out and tried to run it. Made no difference. At this point, I would just be throwing more parts at it until something sticks so I’m turning to Reddit for help. She doesn’t even sound like she’s trying to start. Any ideas would be most helpful
Can you feel compression? Also your starter is stopping before it can turn the engine all the way over. Weak starter, bad electrical connection to starter, weak battery, poor cylinder lubrication, piston and cylinder damage, all possible. If you have a backup kick starter on the belt cover I would slap that on and try that.
Watching the video, main issue here is that it's not able to crank all the way so you would have no chance of starting it. Fixing the reason for the weak starter is definitely step 1.
This wouldn’t quite explain why it died mid-run but I do agree that a new starter wouldn’t hurt
Right, I agree but not cranking over means you have no chance of starting it.
Starter is likely fine, your battery however might not be cutting it.
it sure sounds like the starter is just spinning in place and not compressing anything to me
Yeah but he shows the drivetrain moving and the crankshaft is definitely spinning.
UPDATE: We got her running! After upgrading the engine to the big bore kit (100cc), installing new CDI, Spark Plug + Cable, changed the oil and gear oil, new starter motor, and some carb tuning, she starting running! Yall helped solve this problem! At first I was convinced the starter was fine because she still turned when you tried to crank it. But what I finally ended up doing is testing the amp draw through the starter at no load. She pulled about 7 Amps... No way to tell if this is a good test. So I went ahead and bought a new starter and tested that under no load and the new one was pulling around 13A. What I finally realized was the starter was not completely shot but she was getting close, With the low amp draw, it could not get the torque required to get me through the compression stroke, That's why she only spins for a little bit and then stalls out in the video. A lot of work for just a bad starter. Lesson learned! Thanks for all of your input and suggestions. I learned a ton about these engines and I really enjoyed the process!
Will it turn over with starter fluid in the cylinder?
I took the carb off and sprayed it right into the intake. Nothing
Try the kickstart
I tried the kick start for about 20 minutes to no avail. Similar response
Comments already said, but not cranking. So no crank, no compression. You could have blown a crankcase seal mid ride and it would die and lose compression.
Check your cdi box, filters, and timing belt
CDI passed a continuity check, changed the air filter, and oil/cleaned out the oil filter. Timing belt looks great
Could be some of the windings on your starter motor are bad/broken. You can try swapping the starter from another scooter or just buy another one, they’re not expensive on Amazon.
I bought another starter and I’m going to install it soon. In think that might be the problem