Motobecane Stalls after 5 min

I have a 1977 Motobecane 40TL. It starts fine and runs fine for about 5 minutes then it stalls. I checked for a spark when it stalled and there is a spark. It also seems to be getting gas. I removed the filter box and put my finger over the carb throat and it is damp with gas. Once it sits for about 5 minutes it again starts and runs fine for another 5 min. then stall again. Any suggestions as to what is wrong?

Re: Motobecane Stalls after 5 min

Vapor Lock????????????

Re: Motobecane Stalls after 5 min

I thought of that as well but i checked the vent in the gas cap and it is ok. I also ran it with the cap off and the same thing happens it stalls after about 5 min. of running.

Re: Motobecane Stalls after 5 min

Replace the condenser. old ones stop working well when hot

Re: Motobecane Stalls after 5 min

I have, I think, a similar problem with an '82 PA-50 II

Pardon my ignorance

Would the PA50 have a condensor as well?

Other thoughts?

thanks

Re: Motobecane Stalls after 5 min

Thanks for the reply. When my engine stalls I emediatly checked the spark by disconnecting the spark plug wire from the plug in the engine and connected it to a spare spark plug. I grounded this spare plug by holding it to the engine case. I then turned over the engine to see if the spare plug sparked. The plug showed a nice plue spark. I assumed that because this plug showed a spark that the electrical system including the condenser was funtional. I then reconnected the plug wire to the plug that was still in the engine and tried to start the bike but it would not start. After waiting about five minutes the bike would once again run fine for about 6 miles then stall again. Do you still think it is a faulty condenser? Thanks, Pete

Re: Motobecane Stalls after 5 min

Does it try running a bit with the choke after it stalls? Dan is probably right, it seems that these Motobecanes have troublesome condensers. I've heard you can use a condenser from a General Motors automobile available at Autozone for less than $5. but have never tried it myself.Good luck

Re: Motobecane Stalls after 5 min

Thanks for your responce. I have tried pulling in the choke as it is stalling and after it has stalled I tried to restart using the choke but it did not work. I have also removed the plug and put a small amount of gas/oil directly into the cylinder. I then replaced the plug and tried to start the engine but it still would not start. When I first removed the plug the plug was not wet with gas so I assumed that to motor was getting spark but not gas. I also removed the air cleaner box and held my thumb over the carb throat and thurned the engine over. When i removed my thumb it was wet with gas. To the best of my knowledge and testing it seems that I still have a spark and am still getting gas to the engine but it will not start for about 5 minutes after it has stalled. My thoughts are that I am possibly loosing compression as the engine heats up but think that if it is a compression problem it would show itself before running for about 5 miles.

Re: Motobecane Stalls after 5 min

If I just read your last post correctly you said 5 miles . It it quit after 5 minutes and you go 5 miles then that could be your problem. 60 mph is a bit much.

Bob

Re: Motobecane Stalls after 5 min

Even if the condenser is working fine you should put in another.

Maybe it fixes the problem, maybe it does not. those condensers are bad, and I had similar performance problems (eratic spark when hot)

It is a week spot in the design, so you may as well remove that variable.

I do not think it can be compression. If it was it would not go from running fine, to not running right away. there would probably be a gradual performance loss as it heated up.

Re: Motobecane Stalls after 5 min

I ordered a new condensor today. When it arrives I will install it and hopefully it will solve my problem. I will post results once I have tried the new condensor. Thanks to all for the help.

Re: Motobecane Stalls after 5 min

Dan

I took your advice and replaced the condensor. I have taken the bike for

about a 7 mile ride and everthing is fine. I thank you very much for your

advice. I would have never thought the the condensor would have been the

cause of the bike stalling as it did. Once again Thank You.

Pete

Re: Motobecane Stalls after 5 min

My 77 motobecane does the same thing, where did you get your condensor?

Jim

Re: Motobecane Stalls after 5 min

I also have the same problem and I replaced the condensor. Didn't do anything. Only difference is mine will start right backup without me having to wait. It appears the only time it happens in under load. I have not check for vapor lock yet, I will do that today.

Re: Motobecane Stalls after 5 min

Also wondering where to get a condenser

Re: Motobecane Stalls after 5 min

Aj Fitzgerald Wrote:

-------------------------------------------------------

> I also have the same problem and I replaced the

> condensor. Didn't do anything. Only difference

> is mine will start right backup without me having

> to wait. It appears the only time it happens in

> under load. I have not check for vapor lock yet,

> I will do that today.

I am now experiencing the same issue, replaced condenser twice and still the same problem. She will start up easy and runs well but as soon as I apply the brake she dies straight away or if it take her off the stand or use my shoe to slow the wheel she dies. I have checked for gas and checked the dellorto and no problems there, tried removing gas cap to check for vapour lock and no difference. Any ideas what to check next? Manual suggests air leak at carb to intake or intake to cylinder, could it be air leak at crank seals? Would it be worth doing a leak down test? Hmmm....

Re: Motobecane Stalls after 5 min

♣Slew Foot♣ /

there is a blue wire that runs under the pointset, it goes to the condennsor

sometimes it gets stripped and only under load will it arc. mimicing a bad condensor.

Re: Motobecane Stalls after 5 min

Rollo Tomassi /

I had the same problem a year or two ago. I would get like ten minutes. I tried the stuff mentioned above w/o success. Upon further inspection, the crank bearings were shot. Like the crank rattled around in the cases. Betcha the crank seals were dead too. The motor got a lot hotter in those ten minutes than it should have. I swaped in another av7 that I bought used for cheaper than buying bearings and seals. All is good.

Re: Motobecane Stalls after 5 min

"Vapor lock" you will see nothing but air in the fuel line and it will die at any speed because vapor lock is the fuel unable to reach the engine because it evaporates before it can get there. Very obvious because the fuel line will be completely devoid of fuel (and not just the bubble of fuel in a loop in the line that is normal).

If is it a condenser problem then you will have a weak or feeble spark when it decides to give you trouble. If the spark is blue and snappy then it is not the condenser or coils or points. Could be a weak connection on the bonding strap, which should always be relocated to a intake stud rather then the upper engine mount bolt.

Could be the ignition timing which allows her to drop off at idle.

Also do a leak down test - super easy to do and will verify the containment of the engine. Throw a oring on the intake to carb union when you are done the leak down if it is successful.

Re: Motobecane Stalls after 5 min

Thanks for the responses fellas!

Rebel Moby Wrote:

> Could be the ignition timing which allows her to

> drop off at idle.

Yup was ignition timing, I adjusted it back to points just opening at 2mm before TDC and she's back running good! I'm using the 3/8th extension, cut up ruler and cigarette paper method so it's probably not the most accurate, but it seems that the timing shifted a little over time. Perhaps the fit between the cam and crank shaft is not as good as it was? Is it possible to use some valve grinding paste and lap the two so that the fit is better and hopefully it will not move in the future? I probably did about 250-300 miles before experiencing this problem but I think it slowly got more and more off correct timing until it just wouldn't idle at all. Anyways thanks again now I can take her down to the classic motorcycle show this weekend and park her up outside. VIVE LA RESISTANCE!

Re: Motobecane Stalls after 5 min

Stock Mobys are most happy at 1,5mm BTDC even though the factory spec is 2,0mm for the timing. Yes you can lap the cam to the crank but a taper fit will not easily shift if you clean the cam and shaft with alcohol or brake cleaner (not carb cleaner) and torque the Novi nut to 36lb-ft

She is running fine now so dont mess with her, go enjoy the show this weekend and take lots of pictures!

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