Quadrajet problem

[Red Rex]

M4ME qjet without the mixture solenoid on 350 with Wieand aluminum intake made for q jet carbs but otherwise stock engine. Carb has been on the truck at least the 15 years I have owned it and has been operating fine.

Today it started dying when decelerating to stop, when reaching speeds @ 35 mph and under.

Got it home, opened the hood as saw raw fuel seeping out where the high speed idle cam screw is located below the choke housing and at the base plate gasket where it meets the manifold.

Let it sit a little while, it starts runs fine 40 seconds then dies, seeping fuel as described above. It runs just fine @ 40 mph and above, you would never know there was a problem.

Sticking float or ethanol ruined needle? What say you?

 

[nabeshin]

I am no expert on carbs, but I'd say it definitely needs a rebuild. I think when the speed gets too low the leaks cause it to be too rich and it stalls out. How is it under full throttle? If the float bowl is leaking and not able to get full it would bog at high load. If it is ok at high load, I would guess that the float is stuck and overflowing the bowl - still able to get lots of fuel at full throttle though.

But yeah, aged gaskets are a likely cause or stuck float, I would doubt the casting is cracked.

 

[Red Rex]

Runs great at 2000 rpm and above. Dies below and fuel leaks. Age on the float needle soaked in ethanol fuel lead me to believe the needle tip has degraded and not seating properly allowing the bowl to flood. Could be a stuck float tho. I did try tapping the bowl with my hammer. This has worked on some of the old 1960's vintage cars I have owned.

I will pop the top tomorrow change the needle, and check the float for leakage.

This happened all of a sudden though. May even be some trash caught between the needle and seat.

 

[1987 GMC Jimmy]

So nothing from tapping on it? You could also try a “poor man’s rebuild” before you pull it apart where you put your hand over it to choke it out and see if any obstructions will clear. I’m getting more confident with carbs myself, but I haven’t graduated to Quadrajet level proficiency. The only leaky places I can think of are the well plugs and maybe the primary throttle shaft if you spent a long time cranking or it’s really flooding bad.

 

[HotRodPC]

My original post triplicated. So I deleted 2 of them and it appears it deleted all 3 of them.

So is this is a California Truck? I'm assuming it is if it's an 84 with a Feedback Carb. I'd be getting rid of that carb and starting over with a standard Qjet for a 454,350 or 305.

 

[Red Rex]

Definitely not a California truck. Bought new in Macon Ga and lived it’s whole life through several owners in Georgia. No emissions equipment or wiring under the hood. ECM removed. I use a 6A box and pro billet MSD dizzy. Carb has no provision for electrical mixture control.

I will have to give the poor man’s rebuild a try. I only have one top gasket so opening it up is a reluctant choice.

Turkey season opens Saturday so I gotta get it done

 

[HotRodPC]

Go for the kit if you must, but it probably needs the throttle shafts bushed and the well plugs sealed.

 

[Red Rex]

Removed carb and so far have found loose fasteners base plate to carb body. There is where I saw fuel leakage not out of the bowl vent where it would normally come if float or needle issue. The base plate to manifold gasket is wet with gas as well. I do agree that bushings and well plugs are in order along with a good bath just to ensure internal passages are clean


What is a feedback carb?

 

[DoubleDingo]

Removed carb and so far have found loose fasteners base plate to carb body. There is where I saw fuel leakage not out of the bowl vent where it would normally come if float or needle issue. The base plate to manifold gasket is wet with gas as well. I do agree that bushings and well plugs are in order along with a good bath just to ensure internal passages are clean


What is a feedback carb?

I think the feedback carb is the one with wires going to it. I've only seen pictures of them, never seen one in real life. They're a unicorn to me, but others have seen them.

 

[Snoots]

A Feedback Carb is used with an O2 Sensor to modulate the Air Bleeds in the carb.
Supposed to give you about a 14 to 1 air/fuel ratio.

 

[Octane]

My BogChester float sticks sometimes also.I bought the kit,one day I'll actually rebuild the thing.It has actually ran well since 1977 with only one accelerator pump change

 

[Red Rex]

Fixed the problem. It was indeed the loose base plate to carb body that allowed fuel seepage. Glad I did not have to remove the top. Almost impossible to reuse the gasket

Thing is this carb has been on this truck for at least 15 years with no issues until yesterday going down US 19 just before Griffin gettin out of the Atl. Pulls 16 inches of vacuum prior to this issue.

I see those mixture controlled carbs all the time in junkyards. I am no pro on these things but I do enjoy doing and learning. I am going to call Cliff’s for some advice and parts for one I have on the shelf

 

[Snoots]

You'll like Cliff. Great guy that breathes Q-Jets.
He may be out fishin' tho. Things to have ready:

Year of truck
size of motor
cam profile
type of exhaust
type of intake
Gear ratio
and especially, the number from the side of the carb.
Buy his book too! Great reading.

 

[Red Rex]

Thanks! I have all of it but the cam profile. It is stock as is the rest of the motor. Came from a 1986 3/4 ton suburban vin “m” heavy duty.

4 bolt mains one piece rear engine seal

Only other mods I have in mind are a set of Vortec heads.

I definitely intend to buy Cliff’s book

 

[DoubleDingo]

The vortec heads will need different jets and possibly metering rods