muffler necessity? and is this what they call sei

hey all. ok i have a 79 motobecane moby (smaller backwards-"L" looking muffler faces forward) and needless to say i'm an idiot sometimes and hop curbs and pushed it up stairs and clanged it and whatnot and now the engine block threads are stripped (me being an idiot has already been made clear). so now i just pushed the fitting back into the hole and the clamp is pretty much holding it on so essentially it's not doing anything. and whoo boy is it loud now.

so is this going to effect anything in a negative way? it seems as though i have some extra speed but that's not worth causing damage to her.

as for the seizure talk. i already kinda mentioned this in a post i just made but here goes. ok when i'm out riding for a while or after i've gone up some mean hills (mostly only happens when riding two people) the ped starts to just slow down on its own even when i'm on the accelerator almost to a standstill/stall. when this happens i just stop and give it a rest and then everything returns to normal. is this the beginning of a seizure? i've switched to putting 4 oz to 6-8oz of 2stroke to a gallon because of it.

i'm thinking i should get into the cylinder and check out the piston and stuff but that looks like a bitch to do, and ryan is our resident moped mechanic and he happens to be away at college right now so i'd have to wait for him to return. should i do this and possibly quit riding in the meantime? i don't want to but am totally willing to do so if anyone thinks this could be a major problem and needs to be checked out.

so just let me know asap if you could. thanks.


-moped army-

Re: muffler necessity? and is this what they call

i don't know if that's from an upcoming seizure or not. but check w/ simon on his oil mix. most people seem to use about 3oz per gallon, so you 2oz may have been a bit lean.

i also don't know much about motobecane in general. check w/ simon unless you hear from someone else.

Re: muffler necessity? and is this what they call

Ron Brown /


See my other post on your ped slowing down. Normally, when a 2 cycle siezes, it is a catastrophic event. You can't do anything quickly enough to keep the engine from locking up the rear wheel other than pulling the clutch if you have one.

If your exhaust is loose, you can look at the piston and rings through the exhaust port. This is where you normally see piston problems because of the higher temperatures.

I don't know how you are going to solve the exhausr thread problem. The only permanent sulution is machining and sleeving.

Some older bikes used to use springs, streched between the pipe and the head to hold the pipe in place, maybe you could cobble something like this.

If your exhaust leak is not too large, you have no problem, if it gets too large, you could lean out the mixture. Check the color of the plugs.


Re: muffler necessity? and is this what they call

Chris Robertson /

It sounds like you're putting plenty of oil in the engine.

It does sound like you're describing your engine overheating (and seizing up).

This can be caused by a loose carburetor letting too much air into the engine. This also might have something to do with your (virtually) missing exhaust pipe.

On a two stroke, the exhaust pipe is an important part of the engine, not just a device to reduce noise. It's definitely a good idea to get it fixed.

Were you overheating before you lost your exhaust?

How does your exhaust pipe attach to the engine? Is it two threaded bolts that stick out of the engine and the pipe is held on by some nuts? Is it two threaded holes in the engine that you stick bolts into? Or is it a single threaded attachment on the exhaust pipe that threads into the engine?

Good luck!


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