1977 Mobylette

Matt Van Den Hengel /

I'm writing because I'm stumped as to what's wrong with a 1977 Moby (in gorgeous yellow) that I recently bought. This may get a bit lengthy, but I want to fill you all in from the "git go" as to what I've done so as to eliminate the usual quick diagnoses notes coming back and forth and using precious web space and even more precious web user time.

Symptom: Bike starts up fine when left for a period (i.e. overnight) and rides beautifully (plenty of power, no backfire, smooth throughout rpm range etc) for about 2 miles or so (and that's stop and go moving (red lights and such)) and then (whenever the "problem" starts) if I start to decelerate for a red light, there is this point at which I reach in the rpm range where it just won't come back up. It's almost like I ran out of gas, but that is not the problem. The bike then won't start up again until I let it sit for about 30 minutes or so.

Things I've considered/ done: 1) I first thought I was out of gas. Not the case. The petcock flows smoothly in both on and reserve. Off works well too. I changed the filter (external) and fuel line too. The vent on the gas cap was open (No vacuum lock (I've had that happen to me before--embarassing too)). I checked the float, thinking it was stuck. I ended up sanding down the seam on the float a few thousandths just to "know" that it wasn't touching anything. It works smoother but still the same problem.

2) I pulled the carb and cleaned it up. I then switched carbs with a friend but the same problem.

3) I thought my plug was the wrong heat range, so I switched plugs with a friend, and still the same problem.

4) Then I figured that the exhaust was clogged with carbon, so I pulled it and it is spotless. The same for the piston and the exhaust port. (I was really upset by this because I was convinced that that was the problem.)

5) I knew that I was getting spark the whole time, even when it wouldn't start because I checked and because when I tried to start it, if I held the decompressor lever down a long time, I could hear the backfire in the exhaust, so I knew I was getting spark.

6) The only thing I didn't do was check the point gap, and timing (since it ran beautifully when it ran), but I attacked that yesterday. I filed the points, and regapped them. The timing was off a bit, so I re did that to spec. The bike had slightly less power, but it was running smoothly, and I thought (I've got it now. The timing was a little too far advanced which was good for power but maybe I was getting heat from being really close to preignition (I never heard any pinging.) I rode around the hood but when I reached that critical ~2 miles, the problem came back. Argh!!

Does anybody have any ideas?? I've given the bike to a friend, but she is not mecahnically inclined. Also my pride wants to know that the bike is fixed. Please help me!!

Thank you,

Matt

Re: 1977 Mobylette

Matt,

I seem to remember reading about how a bad condensor would cause symptoms (like intermittent running) that otherwise seemed like a fuel-flow issue. It would work fine when cool, but its performance would falter as it got warm. Search the forum for condensor... I hope it helps!

Re: 1977 Mobylette

CONDENSER!

Dont ride an old moby without a new one

Re: 1977 Mobylette

this could be a zener diode problem as well, if you have some one with a working 76 or 77 swap it out. If it is bad there is one on ebay right now, or i have the answer to making a replacement with common electronics. (i hold the secret to the zener!) ill be happy to share it if you find the zener to be bad.

-backwards

Re: 1977 Mobylette

Matt Van Den Hengel /

Thanx guys,

I'll check on the condenser. I've gone through just about everything else, so hopefully this is it. She runs really great when cold, so ....... Thanx again,

Matt

Re: 1977 Mobylette

Matt Van Den Hengel /

Thanx for the input. I'll check the condenser first, but if it;s the diode, I'll write back and pick your brain. Danke,

Matt

Re: 1977 Mobylette

Matt Van Den Hengel /

Anthony, and Dan, and others,

I know that I run the risk of really sounding stupid on this but I have to ask. Where is the condenser?? I know what it should look like from auto experience. The thing is that I gave the bike to a friend, and I would like to help her get it to be reliable. The manual I had doesn't say anything about the condenser, nor does the wiring diagram in same. I think it should be near the points (duh!) but I honestly don't remember seeing it there. I don't have the bike in front of me to check, and when I do see it again, (travelling time) I'd like to be armed with some more knowledge. Thanx for your time,

Matt

Re: 1977 Mobylette

Condenser is mounted to the stator plate, behind the mag rotor. You'll need to remove the rotor nut, which is a LEFT-HAND thread.

Re: 1977 Mobylette

On mobys before 78 it is inside the stator plate, and I think you have to remove the cam to get at it. On 78 and later it is mounted on the back side of the stator plate

Re: 1977 Mobylette

Matt Van Den Hengel /

Dan, and Legendre,

Thank you for the quick response. (And for not laughing too loud.) Adios for now. I'll write back with a synopsis of how everything turned out. Lindsay (new owner of this Moby) and I thank all of you. Matt

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