77 Motobecane, seized & how to start?

I just got my first moped dumped into my lap. It's a 77 Motobecane and looks to be in cosmetically good shape. However they said the engine was seized. From what I understand, sometimes this is a survivable situation. Ideas? PB Blaster?

Also, what is the procedure for using/starting/stopping the engine on this unit? Someone I know had a tomos that you would pedal backwards to start, but I think it's different for this moped.

On the 77 motobecane, there is what I think is the clutch on the left side with the belt around it. I assume the center is supposed to be turnable? Now, in almost the same position on the RIGHT side is another round item with a square hole... what is it and should it turn?

Any/all info would be very helpful. I'm a beginner with mopeds but I'm a quick learner.



Re: 77 Motobecane, seized & how to start?

Ray Sanders /

Okay, I have a '78 Mobylette 50V that had the same problem.

Remove the spark plug (you may have to remove the long bolt that holds the engine in the mounts to lower the engine far enough)

Spray in some WD-40 and let it sit for a couple of hours.

Remove the chain guards (the white panels on each side of the bike, held in with three flat head screws)

On the other side of your engine (opposite the drive belt) there is a plastic bellhousing, it's held on with three rubber clips. pull the plastic bellhousing, and you'll have something better to use to turn the engine over. Turn towards the front of the bike only. You can wiggle front and back a little, but try not to turn the engine over backwards. If it won't turn, spray in more wd-40 and repeat the procedure.

You may want to clean out the fuel tank if the bike has sat for a while, and the carb may be gummed up. If you can get the engine unstuck, fuel it up (mix 3.6 -4 ounces of 2 cycle oil to 1 gallon of gas) turn the fuel valve to "run" , and turn the ignition switch to on. (same as the horn button)

Get on the bike and pedal like hell. If your decompressor valve works, pop that open while you pedal, and when you get going fast let it out, and it should pop over and start.

If at all possible, find a good motorcycle shop that can work on older stuff... After a few months of trying to get my bike to run well (it runs but not that well just yet) I've decided to drop mine off an have the pro's look at it.

Re: 77 Motobecane (got it unseized, now what?)

Well, Ray, thanks... I got it unseized without too much trouble. I removed the spark plug & sprayed in PB Blaster... let it sit, then yurned it over with a breaker bar... it got easier and eiasier. After about 5-10 times I am now able to turn it by hand now. When I put my thumb over the spark plug hole I'm not strong enough to hold the pressure in (pushes my thumb up)... so I assume it's got compression and that it has a chance of running?

Now, on my 50V '77 Motobecane... can somene explain to me the theory in how it is supposed to work? The only other moped I've seen was a 79 tomos that had to be pedaled backwards to start it. Not so with the motobecane. I can pedal the bike around but what is suppposed to engage the engine when you want it to run? I'm sure that the engine isn't turning all the time you are pedaling so there must be a clutch or something that you engage somehow to start the engine when you want to use it?

Also, on the right side, belt pulley that the pedals turn... there is a little lever like thing on it that you can turn... it moves a little arm on the back of the pulley with a spring that engages into a sprocket... what is this for?

Lastly, on the left handlebar, there is a black platic thing that I think is missing a cap. It pushes like a button, is this the horn? Is it also supposed to turn as a switch?

Thanks for all your help! This is fun!


Re: 77 Motobecane (got it unseized, now what?)

Ray Sanders /

Yes, If you have Compression, fuel and spark the engine WILL Run.

Yes, on the left handlebar is the horn/kill switch. it should be able to turn.

You'll want to turn it clockwise, turning it couter clockwise kills power to the plug (sort of) You'll know if you have the ignition off when you are trying to start the moped as the horn will beep every second or two.

Helpful hints before trying to ride the bike.

Check the brakes, and make sure they work!!!!!!! Test the brakes on level ground, and then find a short incline to test. It's one thing to have brakes that work at 5 M.P.H, and not at 30+ M.P.H

Clean, Clean, Clean out the fuel tank!!!! If the bike has been sitting, you will need to do this.

Also, pull the fuel valve, (tank mounted on left side of bike) and clean it with carb cleaner. Pull off the airbox, and spray some carb cleaner in the throttle body. Try to get a little in the fuel jet (little brass thing in the middle of the air opening.)

Check hoses and belts, and drop in a new spark plug ( changing the plug on motobecanes is a pain in the ass at best.)

I just got my moped running the best it ever has and broke the drive belt at about 20 M.P.H Today. It sucked pedaling it back home (3 miles from where I was when the belt broke) My engine seems okay, and I'm glad I wasn't going full speed, as I may have damaged the engine if I was.

Check the speedometer, does it register when you pedal it?

How long has this bike been sitting?

Re: 77 Motobecane (got it unseized, now what?)

Well, on the carb body, I seem to be missing what you call the airbox. Because there is a square wire clip to hold something big and boxed shape on but nothing else. Is the missing part a filter? What can I substitute with?

See photo of my carb... http://www.mardens.com/moped/

What is the suggested method for cleaning a fuel tank?

There is a black handled switchy thingy on the right handlebar (mine is missing the cable which I'm trying to replace tomorrow). Is this the decompressor valve that starts the engine? Which position is on/off.



Re: 77 Motobecane (got it unseized, now what?)

Ray Sanders /

Yes, you are missing the air box and filter.

Try marksmopeds.com, or mopedjunkyard.com.

If you run the bike without it for too long, you run the risk of it running "lean" and seizing up the engine. Maybe you could look at a diagram, and fashion some sort of an airbox to use.

Yes, the lever underneath the throttle is the decompressor cable.

Don't worry about it being broken. I'd concentrate on the airbox, and getting the bike to start first.

The decompressor by default is off, meaning that you'll have good compression. When you squeeze the lever it opens a small valve (near the spark plug) which basically kills the engine, damn quick.

Re: 77 Motobecane (got it unseized, now what?)

I'm sure I could manufacture something that would work. What's an airbox consist of... a plastic or metal housing with soft block of foam in it as a filter?


Re: 77 Motobecane (got it unseized, now what?)

Simon King /

yep. it's made of plastic and has a wire air filter inside of it, positioned horizontally around the middle of it. i've attached a scan of a diagram that i have so show you the basic shape of the airbox.


Re: 77 Motobecane (got it unseized, now what?)

Simon King /

For some diagrams and photos that might give you a better idea of what goes where be sure to check ot <a href="http://members.tripod.com/~oldlady1/motobecane/front.html"; target="_blank">this site</a>, which is full of scans of a the Motobecane manual. Not very hi-res, but it might be useful.

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