yesterday in the philadelphia area we got 8 or 9 inches of snow. something like that. so we decided to take my motobecane out and all about. i rode a passenger too. all went pretty well as i had my passenger adam put his feet out when necessary to serve as stabilizers. we slipped a bunch of times and only fell once i think. anyways. i know the engine was being more heavily taxed than normal as it had to trudge through the not so freshly plowed snow. but towards the end of our about 2 hour ride we would be riding and then all of a sudden the throttle just didn't matter and the moped just came to a slow stop. i figured overheating and we stopped for a break and then started up again to have it happen again and again. then i just tried to take the most flat/downhill route i could and got home without another problem.

does it sound like just overheating? could it be something else? could this cause damage to the ped? i think this started to happen on my last ride to philly too. if only we had liquid cooled engines.


-moped army-


Re: overheating?

gimmejimmie /

You could have fouled a plug or got some ice in the air cleaner and throttle cable/linkage. Take the air cleaner off so you can see into the carb, twist the grip and see if the throttle slide or butterfly opens completely. Slap a new plug in it and run it through the Mummers parade tomorrow, I'll watch for you getting busted on Action News, ha ha GO EAGLES!!!!

Re: overheating?

As the engine warms up the piston expands a little because of the heat. The cylinder will expand too, but not as much as the piston because they're made of different materials. If the engine overheats the piston will expand so far that it'll get jammed in the cilinder. If the piston gets jammed it'll either slow the enginespeed down dramaticly untill you come to a stop, or it will slow the engine speed down destructifly and some parts inside the engine will break, shatter or bend. Overheating is caused by a lack of lubrication (no oil) and/or a too lean feulmixture. The oil is mixid in the feul, so as long as you don't run on fumes the lubrication should be ok. Because of the cold the air will be thinner causing the feulmixture to be richer, so the mixture wont cause any overheating either. The richer mixture might cause the sparkplug to get damped or even get covered in carbon sediment. I suggest you check the color of the sparkplug to find out what it is exactly. If the plug is blackened you could fix this by installing a slightly smaller main jet in the carburettor, or mount a powerfilter wich will alow more air to pass through the carburettor.

That is backwards

Cold air does not mean the fuel/air ratio gets RICHER.

Cold air means the fuel/air ratio gets LEANER.

Cooler air means denser air... there are more air molecules in a given volume of air.. therefore you are getting more air molecules getting mixed with the same amount of fuel molecules...it is therefore leaner.. and more likely to seize.

People who race often have to change jets for max performance in different temperatures....when it gets colder they put in bigger jets to compensate for the leanness.....warmer = smaller jets...this is common knowledge for them.

The guys problem might be a lean seizure (piston expands and sticks inside the cylinder).. or it might be carb icing (though I am more familiar with 4 strokes doing that only in cold and humid air)..stopping and letting it warm melts the ice and everything is good again.

He can find out fairly easily by popping off the head and cylinder and looking for scuffing on the piston skirt and cylinder.. if none.. no seizure.

Re: That is backwards

Ron Brown /

If the ped is now running OK, I would just check the plug for mixture and up the main jet if it looks lean.

If this is a seizing problem, you can tell when it happens by trying to turn the engine by hand. You will easily feel the resistance to turning.

If the mixture is good and it is seizing up, then you can pull the cylinder and piston and take them to someone who can verify the dimensions.


Re: overheating?

Hey, I'm trying to fix my motobecane because of the same problem. The only thing is, that I live in Florida and mine was doing the same thing after only about a mile and a half. If anyone can figure out what it is I'd like to know, I've been out working on it for 4 hours. -J5

Re: overheating?

hahahahahaha. well m y friend has a motobecane that does exactly this, exept it starts a couple times then u will stop and try to start it but it will not start. i think it may be the coil. but i am not sure. well any coments will be greatly apreciated.

- mike

Re: overheating?

Reeperette /

For you two MotoBecane dudes.

My only suggestion on such limited evidence is to check to make sure you are actually getting compression.

A moped that is not, may start, might even run, but when actual torque is required, it will stall, it will also die for no apparent reason, repeatedly.

Compression is easy enough to check, too - pull the plug, stick yer finger in the hole and have yer buddy crank it. (don't jam yer finger in or you will get scraped/cut this way) - if it kicks yer finger out, you have compression.

If it kicks, but very weakly, have yer bud continue to crank and run yer other hand around the cylinder and see if you can feel where it is leaking from.

If you know you are not getting compression, and you cannot seem to find any leakage, replace the rings.

Still, it doesn't sound like that kind of problem to me, but it is somethin else to check and feel you are accomplishing something, plus it eliminates one element that could be wrong from your list.


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