mobylette compression???

i searched here but was having trouble finding so if it exists im sorry for taking up space and time.

ok heres the issue:

i was working on my mobylette this afternoon and have hit a brick wall.

when i pedal i cant get it to start and stay going. it will start but i will have zero acceleration and when i stop pedaling for about 20 sec. it dies out.

i have spark and my light and horn are operational, and i cleaned out the carburator and air filter.

i think it is the compression cause when i hold my finger down in there i can feel the sucking in but then there is only a lite push up, barely anything.

but it isnt constant it seems this part, see pic, doesnt always turn(forgive me for not knowing the name of this part, i feel retarded ).,

i tried to get it off but to no avail.

if anyone could help i would appreciate it


im retarded i forgot to attach the pic....errrrrr


Re: mobylette compression???

The part in the pic is part of your clutch. This will turn when the engine is turning over (if you are pedaling or if the engine is running). Removing the clutch takes a special tool, which is basically a bolt within a bolt. I bought mine at, and it wasn't cheap.

My Motobecane (a Cady) was doing the same thing. I get spark and gas, but the spark is very weak, so I am replacing the coils and condensor inside my machine. Is your spark a good strong one?

I sometimes think the engine is just compressing and sounds like it is running but isn't.

An engine with good compression should force your finger off of the spark plug hole. Press your finger in there as good as you can to make sure that no compression is escaping around it when you test.

Good luck!

Re: mobylette compression???

yeah i did the finger thing and no luck

the spark seems pretty good. what should i do about the compresion

i checked freds guid and on the search here and wasnt able to find anything?

Re: mobylette compression???

Bad compression is somethimes caused by bad piston rings that have worn out and don't seal right. Gaskets can be a cause too. I haven't had any compression issues so I can't give much advice. This may end up with you taking the engine apart.

Re: mobylette compression???

ok thanx ill check as much as i can first before i resort to that.

ill try checking the timing tomorrow

Re: mobylette compression???

The part in the pic is the clutch, anytime the engine is turning over, the clutch disc will spin. if it is not spinning then the engine is not turning over.

I do not quite understand this sentance

"when i pedal i cant get it to start and stay going. it will start but i will have zero acceleration and when i stop pedaling for about 20 sec. it dies out."

Have you gotten it to fire? Does it only run while you are pedaling it?

Do you have good fuel flow?

put the gas cap on, unhook the gas line to the carb, and let it run out into a gas can.

Is there a steady flow of gas?

I do not think you need to run out and buy a compression gauge yet, even a ped with poor compression will run. they are cheap on ebay though

Compression gauge

screw it on, and pedal. it will show you what your compression is.

Re: mobylette compression???

Actually if you do get a gauge, get one with a long rubber hose. Since the spark plug is in an awkward palce you will need it to get in there

like this

Re: mobylette compression???

i have a gauge but it wont fit in the hole, it is for a car so ill try using a hose as well.

basically the thing only sounds like it is running when i pedal.

the clutch does not catch every time i try to kick it over, i have to pedal like a mad man and wait for it to catch.

when it finally does grab and i stop pedaling the engine sounds like it is still running but when i turn the throttle nothing happens, i do not rev up at all or move forward. then it just dies

what can i do to get the thing to turn over better, is that an ignition timing issue?

Re: mobylette compression???

Do not take your engine apart yet, or even think about putting in a different piston. One of the biggest mistakes people do when trying to fix mopeds is Replacing parts before they have found the problem.

OK it is not running,

-Do you have spark?

If you have spark

-Do you have fuel flow all the way through the engine?

try taking off the exhaust, and placing a piece of cardboard or something infront of the exhaust hole. Now pedal (make sure petcock is in on position) if the exhaust spits gas, then you have gas.

Even if the timing is off, or compression is low you should get it to fire (or backfire)

at least a little

I quote freds guide now

"It takes 3 things for an engine to run.

1... Gas

2... Spark

3... Compression

If your engine doesn't run... 1 of those 3 things is gone.. or not good enough.

(if your engine has all 3 of those things.. IT WILL RUN.. it does not have a choice!)"

Re: mobylette compression???

ok well i have spark i have compression but my plug is dry...

does this mean i dont have gas.?

this may also be part of my problem, when i pull the throttle it doesnt seem to spring back, i have to push it back and then push the cable back down.

could that be part of the prob.?

my choke also seems a little more loose

than my other ped, which runs, could that be part of the prob. also?

ill try the cardboard thing tomorrow. i wish i could bring my ped in my apartment but i have to keep it in a garage in another town so ill be making slow progress.

thanx a ton for the help by the way

Re: mobylette compression???

you know where i could find a guide on how a 2 stoke engine works? i checked the archives and couldnt find anything

Re: mobylette compression???

depends on what you wanna know.. the rabbit hole is deep.

"THIS PAGE": has a pretty good animation and short explainations of how the 2-stroke strokes.. how the engine basically works..

"HERE": is another similar page.. but its got a speed controller and a "pause" button.. (java script)

Just Google "two stroke engine" and lots of stuff comes up .. add particular words to the search for particular subjects.

Re: mobylette compression???


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