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Gerry · Sep 23, 2011

Hi, I am having trouble with my son's 50cc 2 stroke bike engine; I have not been able to identify the make or model, however it appears identical to the motor manufactured by dejun yan zhu (Jiangdu Flying Horse Gasoline Engine Factory. The symptoms are that whilst riding along quite normally it is as if the stop button is held on for several seconds, it then behaves normally again for 30 or 40 seconds before repeating on off on off add infinitum. it doesn't appear to be getting worse but I have tried just about everything including replacing the spark plug and the coil, lapped the cylinder head, disconnected the stop lead and auxillary lighting lead; dismantled and inspected the carburetter. At this stage I am wondering why it doesn't idle very well and if this is in someway connected. .crt.

Any ideas?
Thanks
Gerry

GearNut · Sep 23, 2011

If you are using the stock plug in wire connectors, that could be the problem right there. Those things are junk and should be cut off and discarded. Strip and solder the wire connections and seal them with heat shrink tubing or electrical tape.
If that does not do the trick, check the connections where the blue and black wires attach to the mag. Also check the mag coil's center ground where it is soldered to the mag frame.
Most all soldered connections on these ignitions are poorly done at the factory, cold soldered to be precise.
They need to be unsoldered, cleaned up properly to remove any corrosion and re-soldered correctly.

2door · Sep 23, 2011

Check the connections at both ends of the spark plug wire, especially the boot that connects to the plug. The kit supplied plastic boots are notorious about having a bad electrical connection. Replace it with a good automotive quality boot/terminal. Also check where the wire screws into the CDI for a good connection.
Tom

Al.Fisherman · Sep 23, 2011

Gerry said:
Hi, I am having trouble with my son's 50cc 2 stroke bike engine; I have not been able to identify the make or model, however it appears identical to the motor manufactured by dejun yan zhu (Jiangdu Flying Horse Gasoline Engine Factory. The symptoms are that whilst riding along quite normally it is as if the stop button is held on for several seconds, it then behaves normally again for 30 or 40 seconds before repeating on off on off add infinitum. it doesn't appear to be getting worse but I have tried just about everything including replacing the spark plug and the coil, lapped the cylinder head, disconnected the stop lead and auxillary lighting lead; dismantled and inspected the carburetter. At this stage I am wondering why it doesn't idle very well and if this is in someway connected. Any ideas?
Thanks
Gerry

It sounds like a electrical problem.

1. as mentioned plug and wire
2. also as mentioned connections.
3. Make sure its wired correctly Blue mag to blue CDI. Black mag to black CDI, and while trying to solve the problem, disconnect the kill switch. Cut or cap off white wire from mag, and if possible re solder blue wire on the mag.
4. mag could have a short.

Gerry · Sep 23, 2011

Thanks very much for the quick replys gentleman. I think you are probably right about the HT wiring being rat****, the spark plug cap is very loose and was my next move. I probably overestimated the spark intensity of the magneto, thinking it would overcome the poor connection similar to the spark on a motor vehicle. I was intending to replace it as soon as I could get to town to buy one but didn't think it would be the cause so just kept replacing parts because I had them. Anyway thanks for your help and I will let you know the result later.
Gerry .crt.

Gerry · Sep 24, 2011

hello again, well I replaced the HT plug lead with no noticeable difference, however, I put an adjustable clamp on the fuel line and finally solved the go stop cycle that has been driving me crazy; well I haven't solved it properly but I have at least established that it is getting too much fuel. I had already lowered the float level to no avail and proceeded to lower the needle to its leanest possition, this at least allowed me to get it to idle. It now appears to me that the carburetter is just so basic that it is going to be very difficult to ever get it to run properly. I thought I might see if I can find a more sofisticated carby, perhaps off a chainsaw or lawnmower. Still looking for help.
Thanks, Gerry
.crt.

GearNut · Sep 24, 2011

Which type of carburetor does your engine have?
There are many different types that came with the kits throughout the different years/ different vendors.

All types have been picked to death on this forum in regards to proper troubleshooting and tuning. You should not need to change out the carb unless you simply wish to upgrade it to a better quality one. The kit ones do function adequately for typical puttering around the neighborhood..

Xiodinc · Sep 25, 2011

Ever think that this may be an air leak? sounds like what happened to me today when my carb was loose.

Gerry · Sep 26, 2011

Yes thanks Dan, I have made sure there is a good seal around the carby. I have not been able to devote any more time to it for the moment but I am hopefull that I have found the trouble. The small washer that goes between the spring and the end of the needle valve is missing which I think might be allowing the needle to vibrate around and allow different fuel mixes for any given throtle opening. Will keep you posted as to the results when I replace this washer. Incidentally, the carby is an NT model which everyone seems to think is quite good, but it sure is a basic carby.
Thanks
Gerry .crt.

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