Motobecane problem

Ron Brown /

Just so no one yells at me for not following my own rules.

I have a matched pair of Motobecane model 7's. They were given to me last year and I have cleaned them both up and done all the thigs sugested in Fred's "How to fix your moped".

One of them had too big a main jet so I sleeved it to the size of the small one and that seems to work ok. I also removed the stock air filter from the carb and replaced it with a larger piece of filter foam in the air box after cutting a larger hole. This solved my problem of fuel soaking the air filter.

I have one problem left. One of the peds, depending on the ambient temperature, runs about 10-15 minutes and then dies. After 10-15 minutes, it restarts and runs another 10-15 minutes befor dying. This will repeat for at least 3 cycles, I have not ridden far enough to know if it will repeat indefinitely, although it does not seem to be getting any worse.

I know it dies because the spark goes away. I also know that I do not get a spark from the end of the plug wire so it is not the plug or the plug cover. I have disconnected the kill switch at the coil to eliminate a short in that wire.

I am about to remove the flywheel and check connections in there. If anyone has seen a problem like this, I am open to sugestions.

I will post my progress anyway.


Re: Motobecane problem

Ron,you're a pretty fair mechanic from what I've seen so don't let me insult you here,but I've seen bad coils do this exact thing.You probably already know that coils lose their `umph' with heat and this heat is created by the windings when they are activated to step-up the voltage.Usually it's the coil which fails like this and not the condenser because condensers tend to cause some backfiring or just go dead all at once. Hope it's this simple! BYE!

Re: Motobecane problem

one of two thjings have gone wrong... eather it is seizing then coolling then seizing again or the coil is going dead. i would look into the coil first. then if that doesnt work try the cylinder

Re: Motobecane problem

Ron Brown /


No offence taken, if I did not want sugestions I would not ask.

I had allready decided that I had only the magneto coil, ignition coil, condensor and wiring left to look at. What I was hoping was that someone had seen these same symptoms.

What really bothered me was the cycle time of the problem, 15 mins on, 15 mins off. I would have though that once I got something hot enough to fail, it would fail again quickly the second time.

Anyway, read my other post for an update.


Re: Motobecane problem

Ron Brown /


This was a reading test as well as a help request.

I repeat, I have no spark. The coil call is reasonable, but I think I would have noticed a seized engine while checking for spark.

Read my other post for an update.


Re: Motobecane problem

Ron Brown /

Thanks to Don and Mike for the suggestions. The coil seens to have the vote for "most likely to fail".

I took the flywheel off yesterday to eyeball everything and make some resistance measurements. The magneto coil and ignition coil both had reasonable resistance readings. One ohm or less for the mag coil and ignition primary, 5K ohms for the coil secondary.

Then I found the condensor! Most of you will not find this exiting, but the last time I had the flywheel off to check the points on my other ped, I had not seen a condensor. Well, in typical french fashion, the condensor was mounted on the back side of the magneto, out in all the crud from road and engine, with a wire running through the plate to the coil.

The next most exiting thing was that the condensor read 5k ohms resistance. Still had a kick (some capacitance), but it should not conduct DC power.

The next, almost heart stopping event, was visiting, and realising that a 19.95 part + 5.00 handling + 3.50 shipping leaves me close to $30.00 out of pocket!

It is true, that in typical french fashion, the condensor is a mechanical work of art, however, where it mounts, you can't even see it.

Anyway, I have decided that the motorcycle condensor in my random parts will do, the question is, how to mount it.

Then (imagine sound of dope slap, open palm against forehead), it occured to me that I could mount the condensor next to the coil, make a short adaptor to allow the condensor to connect between the points wire and the coil. As an added feature, the condensor will now be up on the frame, away from the engine and road grime.

More to follow.


Re: Motobecane problem

Ron Brown /

Well, I now have a "new" ignition condensor and the ped fired right up. Of course, it did that before I started so we shall see.

I mounted the condensor on the big engine mount bolt on the left side of the motor, crimped a male spade lug with an extra wire in it, to the end of the condensor wire and a female spade to the end of the extra wire. I used the spade lugs to connect the kill switch wire to the coil pigtail which gets the condensor in the circuit where I need it.

I put the two screws that used to mount the condensor back in the magneto, put a small rubber gromet in the old hole where the wire used to go and plugged the grommet hole. All to keep dirt and water out of the mag.

I polished the points, installed them and re-set the timing.

I am now going to take my usual 40 mile test trip and see what happens. Last time I did this, the ped quit 5 times so it should be a good test. The fact that my favorit breakfast place is on the outbound leg, my local micro-brewery (I'll only have one Miguel) is the destination and the weather is great, are just some things I guess I will have to suffer through.

I am assuming my next post will be Eureka! and not Oh S**t.



Ron Brown /

It worked, made it to breakfast, the brewery and home again. I guess the condensor was the culprit.


Re: Eureka

Hi,Ron! I'm glad to hear you fixed that tough ol' MOTOBECANE. I would have bet on it being a coil problem,but I did see an outside chance of it being the condenser. They must make a pretty tough condenser for it not to have given the usual sudden `pop and stop' symptom.So I've learned something here I'll remember.Thanks for walking us thru this one! BYE!

Fred was right again

Ron Brown /


Fred mentioned in one of his past posts that moped coils very rarely fail. I think I agreed at the time as I have never had a coil on any motorcycle fail.

I suppose a plastic one could crack or a steel case could rust through and cause failure, but I have never seen it.

I have replaced a few auto coils, I suspect that living under the hood where it is hot and providing 4 - 8 sparks per rev may increase the failure rate.


Re: Fred was right again

Hi,Ron! I agree it's rare,but it happens. I talked to another mechanic about this and he said `probably not the condenser,check the coil.' This made me feel better about my guess concerning your problem.He being more stubborn than I, still thinks you'll find a bad coil if you run it for a long run without shutting down.Me, I'm just glad to have learned this info. so I won't discard the condenser `out of hand' because of my past experiences.Also,remember that many lawnmowers are one cyl. and many coils are replaced on them.I've had to do it more than once. BYE!

Re: Fred was right again

Ron Brown /


You should have mentioned to your mechanic that the condensor read 5k ohms instead of infinity. I have taken the same 40 mile ride as I did before I fixed it with no failure. On the previous ride it failed 5 times.

I don't know about lawn mowers but they may suffer from the same environmental conditions as cars, or maybe they are more cheaply made, or maybe it was really the plug wire that failed as they are usually monolithic.


Re: Fred was right again

Hey,Ron! I think I sent an answer to this post to you directly,but it may show up here.Let me know if you receive it,o.k.? I'm a very slow typist(hunt and peck) and it was really just intended for you anyway.I didn't want to re-type it as I'm on a library computer at the moment.The problem I mention is really interesting.I think you'll enjoy the answer to the puzzle(that is,if you don't figure it out first).See ya later!

Re: Fred was right again

Ron Brown /


I took the liberty of pasting your email in here ahead of my response because it confused me and maybe someone will enjoy your puzzle.

>Hi! Now Ron,get real! Call any moped repair shop and

>ask how many failed condensers show up.I'm sure though

>rare, as Fred says,there are many replaced each year

>and anybody knows that anything mechanical can fail at

>any time.

My confusion here is that in my previous post, I wondered if your mechanic would still think my coil was bad, even though my condensor read 5 K ohms, proving that it was bad. I don't recall ever mentioning that condensors rarely fail. In fact, even though I have not seen too many failures, I would assume that they are failure prone, or why would points and condensor normally come together in a tune up kit?

>Let me give you an example of a

>rarity.Problem yesterday: Moped doesn't start.Spark

>plug has very weak spark.The diagnosis normally would

>be pretty easy,right? Not in this case,at least not

>for me.Care to take a stab at it? I solved it

>yesterday by removing the spark plug.The clue is

>`noise',so you don't think I am making this up.Another

>hint is : these don't fail very often either. BYE!

Without the clue, I would have to suspect anything and everything in the ignition circuit, from the magnets in the flywheel to the plug. Given that the clue is "noise", I have to guess you mean RF noise and the plug suppressor cap was bad. I am not sure how you solved it by removing the spark plug, my ped won't run worth a hoot without one.


Re: Fred was right again

Hey! This senile old mind got crossed up.You're right Ron.I kept thinking of coils ,but writing condensers.I was trying to convey that I've seen some coils fail and that any mechanical device can fail and Murphy's law will make sure of that. Thanks for the correction!BYE!

Re: Fred was right again

Ron Brown /


No argument from me, I guess my original point was that if your mechanic had been told that my condensor was leaky, it would most likely have changed his diagnosis and his prediction that the problem would recur.

I still agree with Fred on the coil. I think that coils are often replaced because they are difficult to diagnose without a good understanding of how they work and how to test them.

In any case, given a choice between a condensor and a coil, if I had no way of testing either one, I would allways try a new condensor first because almost any ignition condensor will work, at least until the points burn, so a substitute test is easy, and coils are much more specific and expensive.

On the other hand, I never assume that a coil will never fail, as you can see from Ree's latest posts.

In case anyone is holding thier breath waiting for the answer to your puzzler, here is a copy of your email to me:

Hi,Ron! No, your thinking too hard.It's a `down to

earth,run of the mill noise.I'm just mentioning it

because I was so surprised at the problem.Here's what

happened.I went out to take a long planned moped

excursion(over 60 miles)and when I tried to fire it

up,I couldn't get it to go.I checked for spark and it

was really weak.Now i'm like you,thinking

;Wire,coil,spark plug,points,etc.,when I decide to

crank it really hard by pedaling fast .I heard this

crazy noise like the `Wheel of Fortune'game show has

as the `clicker-pointer'strikes the pegs as the wheel

is rotated.I kept pedaling,put my ear down closer,and

the noise was coming from the horn! It turned out that

the switch failed closed and it drew so much current

that the total magneto charge wouldn't create enough

spark.How's that for strange? So,everybody out there

who has a weak spark should check for a current bleed

off also.This bike has a horn which really draws a lot

of current.I'm wondering if maybe age is getting the

better of it,but it works fine.Just thought I'd share

this weird little occurrence with you guys.BYE!


I have to admit that this is a wierd one. Normally, the horn would run from a completely different winding than the ignition. Are you able to find this connection on the wiring diagram, or is it possibly a short in the wiring?

My Motobecanes blow the horn if the run stop switch is in the stop position, but that is because it closes the horn contacts at the same time as it grounds the ignition (they are both on the same switch). If you try to start it, it quacks to let you know that the ignition is off. The down side is that when you turn the switch off the horn makes a noise like a duck being choked.


Re: Motobecane problem

Hi,Ron! O.K. ,I see where you're coming from on this question and I have to tell you that I suspect that either the horn is severely shorted or my `ped has no separate power coils ,but one source as in a car which is then split into circuits.I have temporarily misplaced my shop manual for the MOTOMARINA ,which as i said is running great now. I will investigate and get back to this forum,asap.BYE!

Re: Fred was right again

Now wait a minute ,Ron! You haven't been strangling ducks again have you? And I had pictured you as a mild-mannered problem solver who would treat one duck the same as the next one,with no prejudice! The only way you're going to get out from under P.E.T.A.(PEOPLE EATING TASTY ANIMALS)on this one is to admit that you bought that #1 selling tape `DUCK-CHUCKING WITH STYLE AND GRACE' . Just thought I'd try to help you get outta' this mess! BYE!

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