Motobecane Clutch Doesn't Engage

Hi, I have two Motobecane 50v's I guess 1978, that I am rebuilding. I am unable to turn over the engine (the wingnut thing is in the correct position). I have taken the engines off the frames and when I turn the inside part of the clutch/variator (the part you pull off with the clutch puller) it doesn't turn the outside part (so it won't turn over the engine).

MY QUESTION IS: should the clutch be able to freewheel like that? I thought it should grab so that you can turn over the engine using the pedals. Also I noticed that the engine can pivot on the top engine mount, does this have anything to do with it? Does there need to be tension on the engine from the pulley in order for the clutch to engage? Also can anyone describe how the clutch on those is supposed to work? (i.e. should it slip at the start when you're idling then engage?).

I have read all the manuals I can find and also tried but can't find a description of the operation.

Thanks for your answers and for the great site.

Re: Motobecane Clutch Doesn't Engage

The clutch will freewheel at low RPMs. I don't think there is any way to spin the clutch fast enough (by hand) to get clutch engagement.

When starting a Moby, you pull in the compression release, then pedal hard. Once the bike is moving a couple mph, the engine should start to turn over. You then drop the compression release, and hit the gas (and maybe give it some choke, if it's cool out).

The engine must pivot ont he upper mounts - this allows the variator (the V in 50V) to operate. The engine will pivot rearwards as the engine hits higher rpms, usually starts around 15 mph. There is a double hairpin spring (part of the lower mount) that keeps the belt tight, and acts as a return for the pivoting engine.

Re: Motobecane Clutch Doesn't Engage

Thanks for your awesome answer : )

With the part where you say "When starting a Moby, you pull in the compression release, then pedal hard. Once the bike is moving a couple mph, the engine should start to turn over." - how do you start it when standing still? Like when you put it up on the stand, and then stand next to it? It says you can do that in the manual, but if the clutch is supposed to freewheel at low RPM how is it possible to kick start it?

Thanks again in advance.

Re: Motobecane Clutch Doesn't Engage

It depends on whether the engine is warmed up or not. I have never tried to start my Moby on the stand, when the engine was cold.

When warmed up, it works fine. I stand on the offside, raise the pedal almost to the top, hold the handlebars, then step down very firmly and briskly on the pedal with my left foot (do not just kick it, follow through to the bottom), and the engine starts. No compression release is needed.

(The offside is the right side of the bike, when you are seated on it. The left is called the nearside).

Re: Motobecane Clutch Doesn't Engage

I always start my 50v on the stand. You open the decompression lever and then press down on one of the pedals. release the decompression lever once it is turning and it should start. it helps if you give it a little throttle. I have at times had to hold the choke lever when it is cold. You also have to hold the choke lever while it is running till it is running pretty strong other wise it will stall out.

Hope this helps.

Re: Motobecane Clutch Doesn't Engage


i have been having trouble getting my moby going but after reading this i think i found the prob.

i have been holding the decomp. lever and the choke to start and i have had trouble going. could that be why, because i am using both?

by the way i got the headlamp ring, its at the post office, unfortunatly i was out when the post man came


moby 50V clutch engagement

Is there a way to make my stock clutch engage a little later?

Re: moby 50V clutch engagement

The Motobecane engine actually has 2 separate clutches .

There is the engine to drive pulley clutch with 2 shoes and 2 springs that stretch at the proper r.p.m. for engagement .

The other clutch has 3 little shoes on a sort of spring steel , and centrifugal force causes them to engage when you pedal it to start.

Re: moby 50V clutch engagement

not sure what moby you're talking about...

My 50v has two clutches. The main drive clutch has four metal arms (not on springs) that come out and grab the clutch bell.

Then it's got two arms on springs, that serve as the starter clutch.

I push start my moby, hold the decomp, push it like 5 yards, starts right up. Can't start mine on the stand because the stand for some reason isn't high enough, back wheel touches the ground a little bit.

Re: moby 50V clutch engagement

Jimbo Grand Daddy /

^^Your stand is probably bent. Moby kickstands are not that good. Rest of the bike is!

Re: moby 50V clutch engagement

Hmm... maybe you're right, hadn't really noticed it. Could be tire size too, or wheel position for the drive-chain tension. Who knows.

Anyway, push starting it is cool, it's quick. I feel like a dope standing on it and pedaling really fast. Quarter-kick is obviously the coolest.

Re: moby 50V clutch engagement

Jimbo Grand Daddy /

Got a couple of quarterkick bikes. Good if you can get it to start that easy!

« Go to Topics — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account