Rochester Q-Jet running rich

[texasmike]

My original carburetor was rebuilt about four years ago and seems to perform well. I've noticed that after a short trip, about forty minutes later when I start the engine and rev it a few times, it blows a few puffs of black smoke. Is this something that can easily be fixed by adjusting the air/fuel mixture screws and if so, which way and how much should they be turned? I am not worried or real concerned about this, just asking. Thanks for your suggestions.

 

[Bextreme04]

My original carburetor was rebuilt about four years ago and seems to perform well. I've noticed that after a short trip, about forty minutes later when I start the engine and rev it a few times, it blows a few puffs of black smoke. Is this something that can easily be fixed by adjusting the air/fuel mixture screws and if so, which way and how much should they be turned? I am not worried or real concerned about this, just asking. Thanks for your suggestions.

I would assume it is working as intended with the choke being applied until warmed up. Did you not do the initial setup of the carburetor after it had been rebuilt? When was the last time that you did a tuneup on the engine(plugs, wires, cap, rotor, etc...)?

 

[Ricko1966]

You don't use mixture screws to correct puffs of black smoke. The mixture screws are to set idle mixture. Adjust them by the book and don't use them as band aids for other problems you'll just create new problems. Do you have a 3 port fuel pump or a 2 port? A 2 port could cause the problem you are talking about. Without a return line when you park heat soak can cause the fuel in the line to create enough pressure to blow the needle and seat open which floods the fuel bowl which dumps a puddle into the intake manifold. Then when you go to start it you have a very rich start.

 

[texasmike]

Thanks guys. The idle is fine, I have a three port fuel pump and it had a complete tune up about 14k miles ago. However, it sure kind of sounds like that fuel pump suggestion. As I remember, that pump puts out 5-1/2 to 6 psi of pressure.

 

[Ricko1966]

Thanks guys. The idle is fine, I have a three port fuel pump and it had a complete tune up about 14k miles ago. However, it sure kind of sounds like that fuel pump suggestion. As I remember, that pump puts out 5-1/2 to 6 psi of pressure.

A 3 port bleeds the pressure back to the tank unless the pump port or the return line is clogged. I suppose that wouldn't be hard to check pull the return line put on a fresh piece and see if you can blow through the line. Put a piece of line on the pump return port put the other end in a bottle run the engine see if you get gas in the bottle.

 

[425HP409]

I would check the float level with a tool to do so with the carb on the engine.

 

[Radiohead]

Is the electric choke cooling off enough to close for the pulloff to not catch up in time? Or is it TBI?

Or some sort of fuel pooling going on in between runs.

Thats what comes to my mind. Something else to check out.

 

[Trucksareforwork]

I must be in the minority here. I wouldn’t chase this “problem.”

You may have the choke adjusted a little too tight so that it runs a little rich after the engine cools off. You may have fuel pooling. But if it runs good and this only happens on a warm restart, I would call it good and go chase something else.

Two puffs of black smoke is just clearing the mechanism.

 

[texasmike]

I must be in the minority here. I wouldn’t chase this “problem.”

You may have the choke adjusted a little too tight so that it runs a little rich after the engine cools off. You may have fuel pooling. But if it runs good and this only happens on a warm restart, I would call it good and go chase something else.

Two puffs of black smoke is just clearing the mechanism.

It's great that this thread is still going. Your suggestion is exactly what I decided to do. I did check the return line and all seems to be OK. The choke is set and operating as it should. The engine starts immediately on hot starts. Next day starts take two pumps of the pedal and starts quickly. More than 2-3 days take a few revolutions to fill the bowl and 1-2 pedal pumps and then starts fine. It's probably the float level but since it runs so good and I don't have the gauge to check it, I'm leaving leaving it alone. I have plenty of other things to tweak.