78 motobecane cuts off after few min.

my '78 motobecane mobylette runs awesome until about 10 min. of riding then slows and cuts off in a matter of a few seconds, sounds like it could be a spark plug problem, but I am just getting into mopeds and am not really sure what the problem is, I have experimented with gas mixtures and different brands of oil, I switched from a champion spark plug (L86C) to a B5HS but no improvement, someone recommended a B6HS so I will try that also I'm goanna put on a fuel filter because it looks like ther could be a little rist in my tank. It has been doing this ever since I'v had it, which is about a year. any help would be help. thanks andrew.

Re: 78 motobecane cuts off after few min.

Check the gas cap vent.After it shuts off, does it start right back up?

Grey

Live to ride, Ride to work

Re: 78 motobecane cuts off after few min.

Mike Scouty McScoutington /

or it could also be a bad condensor.

Re: 78 motobecane cuts off after few min.

no it takes a while for it to restart, probobly about 5 to ten min. and I'm not realy sure what the gas cap valve is but I have checked to make sure gas is getting to the engine by looking at the tube and takeing it off to see if ther is still flow, and there is so that may not be the case.

Re: 78 motobecane cuts off after few min.

how would I know if it is a bad condensor? because I don't know a whole lot about what to look for then something isn't working properly.

Re: 78 motobecane cuts off after few min.

When my friends Maxi did that it was the coil...

Re: 78 motobecane cuts off after few min.

Andrew, the gas cap vent Grey is talking about is in the cap itself... there's a small hole in the middle of the cap that's supposed to let air in (otherwise the tank would have a vaccuum in it as it drained.) Sometimes this vent clogs, and that can reduce your flow of gas to a trickle. If riding with the gas cap off (or just barely on) fixes your problem, you know it's the cap.

I have a '78 Mobylette as well, and after about 3 minutes it loses all power (but will still idle.) So not quite the same problem, but I'm suspicious of my condenser, too. If our bikes are set up the same, it's a small metal can about the diameter of a quarter mounted on the back of your stator plate (that is, on the back of your magneto housing, towards the engine.) You can get a condenser from 1977 Mopeds.

Re: 78 motobecane cuts off after few min.

Mike Scouty McScoutington /

he should have 12 volt system making his condensor a little brown or blue box thast is inside the magneto and under one of the lighting coils.

Re: 78 motobecane cuts off after few min.

Mike, you sure you have that straight? I have a '78 50V, I'm pretty sure it's a 12V system. It has the round, external condensor. Anyway, check out Diagram D, 12 volt startor the round condensor is clearly visible.

Re: 78 motobecane cuts off after few min.

Mike Scouty McScoutington /

it could be either on of the two. some bikes came with external condensors that are the same as the 6 volt condensors, and some had the internal. if you scroll down that link to where they have pictures of the condensors and the points you will see a blue one. That was for a 12 volt system. they changed the design so it would fit internally.

Re: 78 motobecane cuts off after few min.

I believe that I still have good gas flow because when it cuts off I check too see if there is flow to the engine from the tube. Someone said they think maybe its my carb. being dirty or needing a gas filter, I'm going to try a gas filter soon. But maybe its the coil, or wire. because when it boggs down finally it almost seems line its not sparking, (If I pull out the coil wire when I'm riding it does the same sort of thing) so is it something electrical?

Re: 78 motobecane cuts off after few min.

You could see if you still have a spark quite easily with a cheap "in-line" spark tester. I got one from Advance Auto parts for like $5. Put it in line when it stops running and you can tell if its still sparking. You could probably ride just fine with it inline and be able to see your spark the whole way. It worked fine for my car - not sure if it'll do that for a moped though. I solved my own mysterious 10 minute turn off by changing the condensor.

Re: 78 motobecane cuts off after few min.

I recently bought two 77 Motobecanes and after some work both would run fine for about 10 minutes the quit. I would use a spare spark plug and check for a spark and both would have spark but would not run. After sitting for about 10 minutes they would start again and run fine for another 10 minutes the quit again. I had asked for help in this forum and Don Adams suggested that it was a condensor problem. I would have never thought it was a bad condensor because when I used a spare plug I would get a spark. I did buy two new condensors from themopedjunkyard.com and now both the bikes run fine and no longer quit after 10 minutes. I suggest replacing the condensor and if it works thank Don Adams.

Re: 78 motobecane cuts off after few min.

your carb is more than likely dirty, or your fuel lines. get your carb cleaned, put nuts and bolts in your fuel tank with gas and slush it around for a good 10 minutes to get the rust out. just be sure to take the nuts and bolts out when your done cleaning! you could also have a clogged floater on your carb, when this happens your carb wont hold any fuel internally and will deplete thus killing the engine.

Check your exaust. Its a good idea to keep em clean by putting it in a fire or even your grill until it stops smoking, then running water through it to get the carbon out. try putting your finger over the exaust hole (assuming the exaust doesnt leak) if your engine dies then you have good compresion (piston rings) if it keeps running then its most likely your rings or a exaust leak. one more thing, check your air filter, if clogged clean or replace.

its awalys a good idea to keep a filter on any engine, since just a little rust could keep it from running or even dmage your cylinder!

Re: 78 motobecane cuts off after few min.

also depending on what carb you have on your bike...it might be flooding itself out...

i had that problem..ii switched to a delorto and the one i got came with a 70 jet???no idea why ..but it would run for about ten min and shut off.

I also had the bad condensor..pull the wire out of the condensor and look for burnt looking shit on the wire or inside

of the condensor itself...but with that I had no spark..

Re: 78 motobecane cuts off after few min.

Just replace the condensor if you suspect anything wrong with the ignition system. There is no obvious or easy way to test them.

Re: 78 motobecane cuts off after few min.

You might want to consider changing to a higher jet. I'm not sure if you can do that with your carb, but you could be running lean (and HOT), which could cause your piston to over heat and sort of "stick" to the wall of the cylinder. Thats called a soft-sieze and its very dangerous. The easiest way to tell if your running lean is by taking the bike somewhere you can ride it all out for a few minutes. Long straight safe road is best. Get out there with your original plug, then install the brand new plug, get her going and open her up. Floor it for as long as you can, then suddenly turn it off and coast to a stop. Pull the plug, and put back the original. Ride home and look at the plug under bright light. It should be a medium brown on the formerly white insulator nose with no traces of light grey on the side electrode. The side electrode should almost be the same color as it originally was, maybe a bit of deep grey or brown as well.

If you have light grey or a whitish or light brown insulator nose you are running too lean and need to upjet (i.e. increas the amount of fuel that is delivered in the mixture.)

Re: 78 motobecane cuts off after few min.

Mike Scouty McScoutington /

again, with a stock gurtner carb this is hard to do without getting a set of jet bits to drill your own. Gurtner jet are not easy to come by if you can find them at all. this sounds like a classic electrical problem to me. Andrew, while you are taking a look at things make sure you check your ground wire connectings. It will be the wire running from your high coil to your engine mount bolt. mine got really dirty and caused my bike to have so issues like yours as well as when my condensor went.

Re: 78 motobecane cuts off after few min.

cool, I'm gonna look into buying a new condensor than, cleant my tank and my fuel lines and added a fuel filter, it runs better now it feels like but still boggs down after a few min. But I beleve too now that a new condensor is most likely the way to fix this problem. thanks!

Re: 78 motobecane cuts off after few min.

Memories...

Re: 78 motobecane cuts off after few min.

Any Moby person will tell you....it's a bad condenser. Almost all 'cane problems are electrical. Also, ditch that Gurtner.

Re: 78 motobecane cuts off after few min.

haha so did it work out? you changed the condenser and it took care of it? Man, no wonder mobies have such a rep for bad condensers... its been goin on as long as people have been riding them.

Re: 78 motobecane cuts off after few min.

i bet your problem is the gas has been sitting since '05 ;)

Re: 78 motobecane cuts off after few min.

my moby does the same. I have tried everything on this form and it still quits after 10 min. Fires back up, then has no power. I think it must be a fuel issue

Re: 78 motobecane cuts off after few min.

I would say your condensor. I'am sure the other threads have mentioned this as well but I'am too tired to read them now. Best of luck!

Re: 78 motobecane cuts off after few min.

Also I recomend using the stock fuel mix of 4oz of oil to one gallon of gas...32:1 I believe. Also check your plug wire for crappy conections. My 2 cents.

Re: 78 motobecane cuts off after few min.

haha what? Do people not realize this is from 05?

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