'77 Motobecane Carb Issues

Bought a '77 Motebecane 50v in July and have been getting it together. I noticed the carb was leaking fuel everywhere, so I decided to check the float to make sure it was not hung up and installed properly. I checked the float and it was installed pointy side DOWN! I flipped the float and decarbonized everything. Also, upon removal of the carb I noticed there was no gasket between the motor and the carb. Should there be one there? I buttoned everything up and wanted to take a spin. Everything started fine but my performance sucks now. I was doing like 30, now it feels like 10 - 15. I figured I needed to tinker withe fuel / air mixture screw, but when I adjust it nothing happens... AT ALL. All the way in, all the way out it does not stall, and it rides the same speed. This leads me to believe that the adjustment screw was on its last leg. Stripped out or worn out, who knows? Also, I pulled the plug and noticed it was pretty fouled up. I'm not sure if this would affect my mixture problem, but there is some minor leaking around where the float sits. The gasket was in mediocre shape. I really need some suggestions before I go out and buy a new carb. I included a pic of the screw I was talking about...



Re: '77 Motobecane Carb Issues

Any screw with a tension spring behind it is some sort of adjustable screw. My guess is that one is an idle mix screw and wouldn't have much, if any, effect beyond idle..

There's no downside to using gaskets, especially where the carb or intake manifold is involved. .. since someone was messing with that carb there's a chance they left it out. Any slight air/vacuum leak in this area can have a profound efffect on performance.

Get a few new spark plugs to play with .. and it sounds like that carb needs cleaning or float level adjustment if there is one available .. the float is not shutting off fuel for some reason or other. The result is a rich air:fuel mix that would tend to foul the spark plug. Low RPM uses a richer mixture than high speed, where a leaner mix is required, and high speed would suffer most..

Search this forum for info on the Dellorto carbs .. they seem to attract a lot of attention.

Re: '77 Motobecane Carb Issues

The carb in the photo is not a Dellorto - it's a Gurtner.

Gurtner carbs (at least this type) do not have an idle mixture screw; the screw you picture is the idle speed screw. It affects idle speed, and nothing else.

There should be a black rubber gasket (like an o-ring, but flat) inside the mounting flange of the carb. It helps to seal the joint between the carb and manifold. They are frequently missing.

Re: '77 Motobecane Carb Issues

So basiclly, my performance problem is due to either an air leak or float problem. There is no way to make the carb run leaner? If there is, what screw do I have to adjust on the Gurtner.

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