Let's talk mobymatics.

Midlife Crisis Alan /

Got a petcock yesterday for my 77 motobecane 50v, and after some minor carb work got it to fire off. Now, mind you, it doesn't run all that well, it's missing the air cleaner assembly (still not sure exactly what I'm going to do about this) and will idle decently if I restrict the air flow with a piece of cardboard.

Once i got it to run without stalling out I took it out into the alley to see if it would go. And it will. Slightly slower than I can pedal. Giving it gas seems to have no effect whatsoever, it just bogs down more. I can get it to rev up on the center stand, but with rider weight it doesn't seem to want to do anything. The belt is aligned properly and does not appear to be slipping. The engine pulls back as it should and the variator appears to function properly.

Where should I start? I have a decent idea of where to go, but I want to know of any specifics I should look for so I'm not taking shots in the dark. Thanks!


Forgot to mention..

Midlife Crisis Alan /

Things were gettting HOT while I worked on getting the idle right and testing. Too hot, in my opinion, or at least a lot hotter than I'm used to. The engine has a good amount of miles on it, from what I can see (4,000) but the internals looked to be in good shape when I had the exhaust and intake off. Is it possible I'm having bottom-end issues? What should I look for? Everything feels pretty smooth pedaling and sounds fine running, though the clutch is pretty loud (as seems to be the case with motobecanes)

Re: Forgot to mention..

It sounds like you're running super-lean. I wouldn't run it too much until you've fixed the problem. You're either getting too much air, like and airleak in your intake or bottom end seals, or your not getting enough gas, like your jet is clogged, or your float is misset, or your fuel supply restricted by a clogged fuel filter, or your idle circuit is clogged.

Does your choke work? The gurtner choke is a enrichment circuit rather than a air retriction, so using the choke should give your engine more fuel and try to even out the lean running condition.

Re: Forgot to mention..

Midlife Crisis Alan /

Bret -

The choke has no discernible effect, and I'm unclear as to how it works within the system - I'm assuming the cable opens a passageway in the carb to let more fuel in, but where does this occur?

I also realized that I didn't take out the emulsion tube when I was cleaning the carb, I just blew air through it, so I'll take it out tonight and see if it's gummed up.

How can you adjust the float? it's just a bobber with a post at one end and a needle at the other, I don't see a way to change that.

Thanks for the tips - I'll dive back in.

Re: Forgot to mention..

The float can be positioned by sliding it up or down the needle.

Clean that carb out well, and put in a clear fuel line so you can see the gas flow to the carb.

the higher hole in the carb bowl takes a long curvey path to the idle circuit, which is 2 small holes near the diffuser.

the choke slide opens up a path directly into the Barrel

Re: Forgot to mention..

Midlife Crisis Alan /

Well, forgive my "duh, duh" moment on the float. That makes a little too much sense for me not to realize.

I've got the new fuel line and petcock, so I'm keeping a trained eye on what's going in - it's what's already in there that I neglected to clean out that has me worried.

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