50cc longjia lj50qt 3-l wiring fault?

my sons Chinese moped when switched on will show the fuel gauge level and indicators work, but once he set off moving they fail and when he stops again they work ok. does anyone have any suggestions where I can pin point the fault or general area I need to be looking for the problems. I can fix most things but wiring is my weakness. 

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MichealH12 (author) 29 days ago

now here is the kicker!!! he went to college on it yesterday and there was nothing wrong with it, not one gremlin in the wiring. so I will monitor it and see what happens, but it is driving me nuts as I hate a mystery I need to know why and what caused it. anyway thanks for all the suggestions you guys have been brilliant.

Deep in sadness I must tell you this sorry fact... That oriental moped just does not like you :-(

it's hard to guess sometimes without seeing it in front of you or not having a wiring diagram to look at. But from what you are saying, the problem develops when you are moving or the engine revs up. If you put the unit on the center stand (the one that lifts the wheels off the ground) and rev it up so the wheel is spinning (be careful not to launch the scooter), do the gauges/indicators quit working? I'm just wondering if there is a wire that is shorting out that goes up to the gauges/lights, or if something is taking away the power when it revs up. Do the lights just cut out or do they slowly fade out?

MichealH12 (author)  cerberustugowar1 month ago

i had it on the stand with the engine running the fuel gauge and indicators were working and then when I held the back brake on they just stop working, so I released the brake but they would not work not until I stopped the engine and turned the key off then restarted the engine.

Sounds like a processor gone haywire... Do a real reset, by removing the battery and pressing the hand brake..

MichealH12 (author)  iceng1 month ago

thanks ill try that. I being doing a bit of research and was wondering if the voltage regulator/ rectifier regulator could have something to do with as it will not start with starter motor but it kicks of ok as well

does the starter work on the bench or when you bypass the solinoid. Just weird why the starter wouldn't work unless the battery or the wiring was bad.

You have checked the battery voltage and checked it again while it's running to make sure the unit is charging? While it's running, try putting the meter on AC volts and measure across the battery. I believe you are allowed upto 0.5VAC (they call it ripple voltage). If you have more than that, you might have a blown diode in your rectifier. .

I don't think so, a starter motor is a high battery current machine and in your case is switched by a heavy relay == contactor..

I would place a voltmeter across the two wires and see what happens when you start.. BTW I stick two needles into the vinyl wire an inch apart to measure...

If there is no voltage then it is the controller if it gets battery voltage then tryto see if the start motor gets battery voltage...

MichealH12 (author)  cerberustugowar1 month ago

the lights are ok it is just the fuel gauge and indicators which die

rickharris1 month ago

A quick troll of the web suggests these vehicles have a LOT of electrical problems.

Don't know your model but if it is like most of these nasty mini bikes then your problem is simply where the bike came from.
I was asked to help out for a while fixing bikes and sadly the shop also agreed to take on repairs for bikesthey did not sell, including motorised ones...
In literally every case with electrical funnies like yours we ended up replacing the entire wiring.
The problems start with loose connections and contects that corrode on contact with water, goes over to far too thin wires used on lamps and ends with stuff rattling loose everywhere.
These toys are designed to run for a season and then to be placed into a recycle bin ;)

If you want to waste a lot of time then use a testlight to check all wiring, especially if you can't reproduce the problem in all cases on a stand you will need more beer and swear words than what is good for you.
If you want to get rid of the problem for good then open up the wiring write down what connectors you need and then replace the lot wire by wire.
Where possible prefer soldering over push on connectors but leave things like the ECU with the original connectors unless they are too crappy.

MichealH12 (author)  Downunder35m1 month ago

i think your right matey! already swearing at the thing and restraining myself from kicking it. anything else I can fix, but f*****g wiring its like looking for a needle in a haystack. oh well! at least it gives me something to do over xmas. cheers for all the guys who have suggested things and please keep suggesting on where the problem might be I would be a happy camper

iceng1 month ago

What it sounds like, meters work when on battery and IC engine not running but when ignition is firing the spark plug that battery cannot supply all..

Leading the inevitable conclusion that the engine is not replenishing (generating) electrical power..

Try when the meters are working turn on the headlight if it has one ?

MichealH12 (author)  iceng1 month ago

thanks for the reply I charged the battery up and the headlight is on all the time

one of those Chinese things I guess. the fuel gauge and indicators work whilst engine is running, but when going down the road on it they cut out and no indicators.

Sorry you are in that area that would need me to use my hands tracing wires and a meter to unscramble...

BTW how long did you use it before this annoying thing started to happne ?