old mobylette

A friend of mine and I were recently left with an old 1970 Motobecane Mobylette to get running. The bike has only 1100 miles on it so should be in good shape, but has not been on the road in at least two decades. As reasonably experienced "wrenches" we thought this would be a simple thing. After a partial teardown, we found a broken ring and a clogged up carb, but after ring replacement, a complete stripcleaning of the carb and some fiddling it sort of ran. We can start it by peddling on the centre stand, but it won't rev up nor hold an idle after that. Possibly part of our problem is we don't really understand how these machines are meant to be operated. We assume you simply start peddling these with the throttle on opposite lock then once up to speed, move the throttle and it starts. Is it then supposed to stay running? Or does the starting procedure need to take place again after each stop? Also does anyone have some initial set up specs for the carb...how much should the slider be open at idle...what about a starting mixture setting? Any other ideas gratefully accepted. Thanks in advance.

Re: old mobylette

mopeds once started should stay on. If they dont they arnt getting enough air or gas and or it has a weak spark.

Re: old mobylette

Did you check the compression? If you found a broken ring, what shape was the cylinder wall in? What kind of spark are you getting? Did you clean the points? These things in addition to fuel flow must be checked before trying to run a moped.

Re: old mobylette

I does seem to have quite good compression (based on a simple finger over the plug hole). I think the old thing is mag-fired, but I have don't want to go there until I have exhausted all other areas...it certainly has very good spark. However I don't know if there is some kind of advance mechanism in there as there is on old English "mag" motorcycles. There also seems to be plenty of fuel getting to the carb and the float system seems fine...at least it shut off the fuel once the bowl is full. And it does run...just won't stay running or idle. Bore was unmarked when we took it apart, but we did rough it up with a wheel cylinder hone to enable the new ring to break in.

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