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Post by dabbound on Sept 19, 2020 13:20:08 GMT -5
I have a 50 cc scooter with a 80 cc big bore kit installed it worked great for a year, but then it started having a problem where when you are accelerating it start feeling like it is pulling backwards or hesitating. It doesn't let me go over 40 mph and used to top out at 50mph. When it gets to about 35-40 it starts doing that pulling back thing and then speed drops. I know there is a governor or something that prevents it from going over a certain speed but that was never a problem before . Could it all of a sudden start be a problem or is it something else. Also, it seems like the problem gets worse I have had to replace the big bore kit 4 times in 2 years not sure if it is related to this problem or was something else. If anyone has any ideas what it could be please I could use all the information and help
I can get. Thank you
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Petro
Scoot Enthusiast
Posts: 149
Location: Gothenburg, Sweden.
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Post by Petro on Sept 20, 2020 9:02:10 GMT -5
On the hesitating matter, I would move the needle (in the carburetor) to lean first and then to rich. That would tell You a lot and might even be enough. If it runs fine/better rich from 3-7k RPM I would suggest a larger jet. If it runs fine/better lean at the same RPM's go for a smaller jet. If You are able to, make a compression test too.
Changing 4 sets of cylinders in two years is only telling me that they must had been melted "chinese soda cans" as we say here in Sweden...
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Post by GrumpyUnk on Sept 20, 2020 10:22:38 GMT -5
Given it worked 'yesterday' but runs different now, something has changed. It is possible the fuel filter has accumulated a slight amoutnt of 'stuff' that is slowing the fuel flow. In that case, you would start to run a bit 'lean' when the demand for fuel outran the supply, and you would get the symptoms described.
The inside of the fuel line could also be disintegrating, the fuel outlet screen in the bottom of the tank could be partially blocked by stuff. It has a tube with sections that are 'screen'. If the screen gets clogged, flow may be limited. The petcock could have a pinhole in the diaphragm, which could allow the valve to close, or partially close, or oscillate again limiting fuel flow.
If you want to verify it is fuel related, get a portable fuel tank, connect to the carburetor fuel inlet, and take a test drive. Should be fun holding a tank, steering, braking, and balancing all at once... Ha..
Last item of thought is the carburetor itself. There could be junk in the trunk(float bowl) that is blocking flow throught the main jet, or intermittently blocking, picked up when the flow is greatest, and plopping to the bottom when demand falls. Ditto with the stuff in the tank, flowing and blocking when demand is highest, and then falling to the bottom when demand decreases.
tom
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