1976 Motobecane 50 stalls when it gets warm

My 1976 Motobecane Mobylette 50 (non-variated) runs absolutely great when it is cold. Starts right up and goes for 1 - 3 miles, then she starts bogging down, and will stall as soon as I come to a stop. If I then wait 15 minutes she will start right up again?

Thoughts? I am very new at 2 stroke mopeds.

Thanks!

Moby 1.jpg

Re: 1976 Motobecane 50 stalls when it gets warm

It is very stock. It has a 54 jet in it.

Re: 1976 Motobecane 50 stalls when it gets warm

Could be an air leak. Maybe a crank seal or the decomp?

Tighten up the head bolts a little, I was chasing a similar broblem on my Moby that was a loose head bolt

Re: 1976 Motobecane 50 stalls when it gets warm

Sounds like a bad condenser to me, see Wiki for how to mount an external one, under Rebel Moby.

Re: 1976 Motobecane 50 stalls when it gets warm

Rick Bergsma /

> Stephen Keller Wrote:

> -------------------------------------------------------

> Sounds like a bad condenser to me, see Wiki for how to mount an external

> one, under Rebel Moby.

Bad condenser for sure

Re: 1976 Motobecane 50 stalls when it gets warm

Thanks guys! New condenser on the way (Treats has an 18% off sale right now!).

Side note, I was chasing the carb adjustment route (I thought it was running lean and getting too hot), so I bought a Delorto 15.15 for it. Should I install that as well? My main goal is RELIABLE performance, not necessarily more speed.

Re: 1976 Motobecane 50 stalls when it gets warm

Best plan for the condenser is to upgrade to a external mounted condenser. If you scored yourself a stock condenser you can mount it on the back of the Novi 120x magneto (look on the back of the plate and use a small self tap screw). OR you can use a mid-1960s GM-Delco 6 cylinder (or similar vintage VW-Bosch) condenser and mount it to the lower external coil's mounting stud. Any of those you just need to splice the pigtail into the grey wire that goes to the external coil, then disconnect the blueblack wire going from the original condenser to the points.

While inside the magneto it is a good opportunity to clean and gap the points at index to 0,4mm and set the timing to 1,5mm BTDC.

You would also want to ward off other electrical issues by replacing the bonding strap that goes from the upper engine mount long bolt to the external coil. Fabricate a new wire to go from one of the intake studs to the lower stud of the external coil. This will provide a good electrical bonding (common or ground) between the motor and the bike.

If you scored a SHA15:15 then get your self a 60 or 62 jet for it as well as the 15mm intake. Putting the 15mm carb on a stock intake will be hell to tune and give more troubles than you want to get it set up. The 15mm intake you will likely need to derestrict the area where it transitions from round bore to rectangle, it necks down in that area and you need 15mm through the entire round part.

Get a 11/16 X 13/16 X 1/16 oring for the union between SHA and intake manifold to ward against vacuum leaks.

I would also suggest to get a new crush washer for the exhause, and remove the exhause so you can clean it and the exhause port window. You always need to use a new crush washer to reinstall the exhause, and after it is installed take the bike for a goodly run and check the big nut it right tight while the engine is cooking hot. If the big nut is not well secured then the vibrations of the motor can loosen the nut and it will ruin the threads in the cylinder.

> Phil Burtner Wrote:

> -------------------------------------------------------

> Thanks guys! New condenser on the way (Treats has an 18% off sale right

> now!).

>

> Side note, I was chasing the carb adjustment route (I thought it was

> running lean and getting too hot), so I bought a Delorto 15.15 for it.

> Should I install that as well? My main goal is RELIABLE performance,

> not necessarily more speed.

Re: 1976 Motobecane 50 stalls when it gets warm

This is really great advice. I appreciate it. Any chance of getting a photo of where to mount the condenser. I am new at this, so practically everything I do, I am doing for the first time. I have never removed a magneto.

Thanks, Phil

Re: 1976 Motobecane 50 stalls when it gets warm

Hoping these pictures will assist you in the condenser relocation.

Stock location inside the magneto

CondenserLocation.jpg

Install replacement location at back of the stator plate

backofstator.jpg

Optional install location on the external coil mounting stud

CondenserInstallation_016.jpg

(edited)

Re: 1976 Motobecane 50 stalls when it gets warm

Well, that coil mounted option looks pretty easy. Is there an existing electrical connection point there? It looks like you just disconnected an existing connector and reconnected the new condenser to the coil side of the the existing connector. I assume the disconnected side goes down to the bad condenser?

Re: 1976 Motobecane 50 stalls when it gets warm

You can not see the splice that goes to the external coil primary terminal but it is there...

Original condenser as seen in the top picture is wired directly to the points - blue wire with back tracer - you need to disconnect it from the points. If you do not remove the original condenser, cut the pigtail short and make sure the wire will not foul in anything moving.

> Phil Burtner Wrote:

> -------------------------------------------------------

> Well, that coil mounted option looks pretty easy. Is there an existing

> electrical connection point there? It looks like you just disconnected

> an existing connector and reconnected the new condenser to the coil side

> of the the existing connector. I assume the disconnected side goes down

> to the bad condenser?

Re: 1976 Motobecane 50 stalls when it gets warm

OK, I apologize for all the questions, but to me, this is really complicated, and I don't really understand it. Check that, I understand it just enough to be dangerous!

So I will need to open the magneto to either remove or disconnect the faulty condenser. Then while I'm in there, I clean and adjust the points and close it back up. Then I attach the new condenser to the coil mount and attach the condenser lead to the coil primary terminal. Will a newbie like me be able to recognize the primary terminal (with there be a + on it)? Will I need to solder or is attached by a screw?

I'm wondering why I would not replace the condenser in its current location? Is it a bitch to remove?

THX!!!

Re: 1976 Motobecane 50 stalls when it gets warm

They don't like heat, and it gets hot in there, external keeps them lasting a while, and easy to replace.

Re: 1976 Motobecane 50 stalls when it gets warm

Echo what Steve posted - heat is the enemy of capacitors and heat is a by product of generating electricity ina magneto. Novi magnetos are not vented so the replacement would cook like the original one did.

Only three wires at the external coil, the bonding strap which is attached to one of the mounting studs, the spark plug wire, and the grey primary wire. Only one spade terminal on the Novi coils, which is for the primary wire. You can strip a little insulation on the grey wire, splice on the pigtail from the condenser, solder if you wish, then tape it, or use shrink tube, or goop it with RTV.

> Stephen Keller Wrote:

> -------------------------------------------------------

> They don't like heat, and it gets hot in there, external keeps them

> lasting a while, and easy to replace.

> Phil Burtner Wrote:

> -------------------------------------------------------

> OK, I apologize for all the questions, but to me, this is really

> complicated, and I don't really understand it. Check that, I understand

> it just enough to be dangerous!

>

> So I will need to open the magneto to either remove or disconnect the

> faulty condenser. Then while I'm in there, I clean and adjust the

> points and close it back up. Then I attach the new condenser to the

> coil mount and attach the condenser lead to the coil primary terminal.

> Will a newbie like me be able to recognize the primary terminal (with

> there be a + on it)? Will I need to solder or is attached by a screw?

>

> I'm wondering why I would not replace the condenser in its current

> location? Is it a bitch to remove?

>

> THX!!!

Re: 1976 Motobecane 50 stalls when it gets warm

Great info folks. I think I got it... as long as I can open the magneto to disconnect the faulty condenser. I'll post some photos of the project. I think I'll do the condenser replacement first, then do the carb replacement afterwards.

Re: 1976 Motobecane 50 stalls when it gets warm

That Novi nut is a left thread, it will be tight and you have to turn it backwards to loosen. Trick with a #72 hose clamp (plumbing section clamp for the 4 inches PVC pipes) and a block of wood to stop the crank from rotating while you loosen works well.

> Phil Burtner Wrote:

> -------------------------------------------------------

> Great info folks. I think I got it... as long as I can open the magneto

> to disconnect the faulty condenser. I'll post some photos of the

> project. I think I'll do the condenser replacement first, then do the

> carb replacement afterwards.

NoviGennyOpen.jpg

Re: 1976 Motobecane 50 stalls when it gets warm

I use a ratchet strap around the flywheel and hooked someplace rearward . Works great for me .

Re: 1976 Motobecane 50 stalls when it gets warm

Belt strap works good

Re: 1976 Motobecane 50 stalls when it gets warm

Sounds to me that the bike is running out of fuel.

Have you cleaned the screens in/on the petcock?

Mike

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