Motobecane, run only with lights on

I have a lot of trouble trying to figure out why mopeds have spark issues when the lights are working or not. Today I was riding for a while with my kids and aftera few miles we came to a stop and my 50V stalled (which it never does). I tried to start it and it wouldn't even sputter till I turned on the lights then away it went running normally. Switch off the lightsand it would stall?? I can't find anything wrong with the wiring or connections. I pulled the flywheel and checked everything and it looked good resistance in the coils seem about equal. I found the tail light bulb was burnt out but that wasn't on when it stalled and wouldn't start. I put it back together and now it runs normally again with or without the lights on. Can anyone enlighten me as to why mopeds use the lights as part of the spark equation? TIA DT

Re: Motobecane, run only with lights on

I have the same exact problem. I heard MBK's have some wierd wiring. Leave it to the French to complicate something simple. I need to check my bulb now.

Re: Motobecane, run only with lights on

I think it is a 'safety feature' - i.e: so you can't ride without a brake light. Legendre is really the guy to ask.

Re: Motobecane, run only with lights on

_ I heard MBK’s have some wierd wiring_

You heard right, my friend. The 12V (1978 and later) Motobecanes have a fairly sane wiring system, but the earlier 6V systems are pretty bizzare. If a connection shorts out, or opens up, you can get all kinds of strange effects.

I hope to one day publish a complete new wiring diagram, that is actually useful, along with some circuit analysis, explaining how things work. One thing of note, is that the system operates very differently when the lights are on, as opposed to off.

Before I corrected an issue with my tail light and a brake switch, the bike would not run unless the lights were turned on. I'm still trying to understand why.

Re: Motobecane, run only with lights on

I had the same issue with a motobecane.

I have a simple solution

run it with the headlights on

Why would you ever want the headlamp off?

Re: Motobecane, run only with lights on

Michael Dane /

more observation on this strange phenomenon.. I rode this v50 about a mile and a half and coming to a stop it stalled and wouldn't restart. I was able to get it running after a while by turning on the lights. When I was almost home it stalled again and wouldn't restart even with the lights on. I checked the resistance in the coils and all seemed ok. I put everthing back together and it ran perfectly. I took it out again today an it did exactly the same routine as before. I believe my problem is heat related because after it cooled down for about an hour it started and ran perfectly again. Think it might be the condensor? I also have new coils in stock but since all the lights are working I suspect they are ok. The secondary coil was actually cool to the touch when it stalled. Thanks for any input here. DT

Re: Motobecane, run only with lights on

CONDENSER!

or gas cap vent

Re: Motobecane, run only with lights on

Michael Dane /

I know its not the gas cap vent because i tried that. The bike spent a lot of time in a damp climate as evidenced by the amount of rust on everthing. maybe some moisture ruined the condenser. My other v50 had a bad condensor and the engine always sputtered. Thanks for the tip. I've got a few nos condensers so I'll give it a try.

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