Cause for very rich mixture ?

[quant55]

Hello,

 

I have two carbs with this symptom. It is so rich that if I totally close the mixture screw I'm seeing the engine idle is increasing. The same if I'm removing the blind plug from the carburateur joints, the idle rpm is increasing a lot. Also the spark plugs are black.

 

Can someone to advise on causes for very rich mixture?

 

The facts: The large diaphragms have no holes and the sliders are moving freely. All the jets are clear. The air cut off diaphragms have one small hole (each of them actually, on all 4 carbs).

 

Might the air cut off diaphragm be the cause for very rich mixture? What else should I check?

 

Thank you!

[MiCarl]

The air cut of diaphragms are probably not causing it to be rich. They're more likely to make it go lean. They should be replaced though.

 

The most likely reason for rich is float level set too high or float needles leaking. After that you need to look into whether it has the correct jets or potentially someone enlarged them cleaning with a piece of wire. It's also possible the gasket on the jet block is leaking and allowing extra fuel in.

[quant55]

I'll replace the air cut off diaphragm on tomorrow. Float needle leaking and jet block gasket... I'll check them tomorrow as well. Thanks. I'll come back tomorrow with news.

[BlueSky]

And of course look at the choke plates to make sure they are not sticking.

[MiCarl]

And of course look at the choke plates to make sure they are not sticking.

[quant55]

And of course look at the choke plates to make sure they are not sticking.

 

As I promised I am back. I checked the choke, but it was fine. I replaced the air cut off diaphragms then I did a carb re-sync and now everything is as it was supposed to be.

 

Thanks for your help!