Rochester Quadrajet

[DozerII]

Really need some help with the carb problem on my 29 Essex build.

I don't have any back ground on the motor other than it is an 81 Gmc 350 that is stock. Good compression and oil pressure. It had a cast intake with all the emission fittings all over the place, I replaced it with a Jegs aluminum performer clone. I rebuilt the original Quadrajet, but was real concerned about it, as it was very badly corroded on the inside and all the steel parts. After the rebuild the motor ran really lean and no amount of adjusting would fix it, so I broke down and ordered a carb, my first gut feeling was to order an Edelbrock 1406 and second guessed myself and ordered a reman Quadrajet. When I installed this carb I also installed a 1" aluminum spacer between the intake and carb.
From the initial fire it ran really rich, lots of black smoke and a terrible bog. It has an electric choke which I turned all the way lean to rule it out, no help. I called the re-builder and he suggested taking out the idle jets and blowing carb cleaner in, and taping the front fuel bowl area to loosen a stuck float / needle from shipping, none of which made any difference. He then said to pull the top off the carb and physically check the float all good and set to 3/8"just like spec say.
I checked the jet size and the original carb had #71 and this one has #72 also the secondary metering rods are slightly smaller in Dia. and different taper. I put it back together and fired it up and it put out so much black smoke it burned my eyes.
I'm running between 14.5 and 15.5"of vacuum at idle, but have found turning the idle screws all the way in does not change how the motor runs very much and only drops the vacuum by about 2"
I have sprayed flammable gas around all possible spots there could be a vacuum leak with no increase in rpm.
I have exhausted all my knowledge, hope one or more of you wise men can lead me in the right direction.[S[S

Thanks in advance.

 

[Dr Crankenstein]

Closing your idle mixture screws should kill the engine.

What's your idle speed/RPM?

.

 

[DozerII]

Closing your idle mixture screws should kill the engine.

What's your idle speed/RPM?

.

That is what I thought? idle is between 600 and 700 in park.

 

[Old Iron]

Send it back!!!!

 

[05snopro440]

Do you have an intake leak?

 

[bob w]

Sounds like the metering rods are staying in the "up" position. The piston is pulled down by vacuum. Sometimes the top gasket can interfere with their movement.

 

[DozerII]

Do you have an intake leak?

Not that I can find by spraying a flamable aerosol around all possible spots while it's running

Sounds like the metering rods are staying in the "up" position. The piston is pulled down by vacuum. Sometimes the top gasket can interfere with their movement.

I checked there movement after prior to putting the top back on.

Send it back!!!!

I'm working on that

 

[smallfoot]

If the price difference wasn't too much, I'd have gone with the Edelbrock, IMHO. I always use the 1405 down here. No electric choke, infact no manual either. I could put a cable on it for manual but a sound sbc can be started from static timing and first setting with an Edelbrock in the temps we get. No gaskets below the fuel level keeps em leak free. You can check the fuel bowls by separating the top and leave the rest in place. They're pretty simple for an old simple guy like me. I ran QJs, Holleys and Edelbrocks and since I went to them, I haven't gone back to any others.

 

[BlueNorther]

somewhere in the late 70's early 80' all the carb mfg's changed to reverse idle mixture screws, and limited how rich they could go. the later idle screws actually meter the air mixed with gas through the idle air port. turning the screws in will richen (less air) the mixture while backing them out leans (more air) the mixture.

also check the fuel line pressure QJ's don't like more than 6psi.

 

[DozerII]

If the price difference wasn't too much, I'd have gone with the Edelbrock, IMHO. I always use the 1405 down here. No electric choke, infact no manual either. I could put a cable on it for manual but a sound sbc can be started from static timing and first setting with an Edelbrock in the temps we get. No gaskets below the fuel level keeps em leak free. You can check the fuel bowls by separating the top and leave the rest in place. They're pretty simple for an old simple guy like me. I ran QJs, Holleys and Edelbrocks and since I went to them, I haven't gone back to any others.

Thanks, I sent it back no refunds he says he will send me another one, wish I would have gone with the Edlebrock

somewhere in the late 70's early 80' all the carb mfg's changed to reverse idle mixture screws, and limited how rich they could go. the later idle screws actually meter the air mixed with gas through the idle air port. turning the screws in will richen (less air) the mixture while backing them out leans (more air) the mixture.

also check the fuel line pressure QJ's don't like more than 6psi.

Thanks BN, I will have to figure out how to check the fuel line pressure. I took and old Qjet I had and cleaned it as best I could put an new needle and seat in and an accelerator pump, although not perfect the motor runs way better with it than the new one I sent back.

 

[05snopro440]

If you're trying to find intake or vacuum leaks you can take a plastic one-use water bottle and poke a hole in the lid. Fill with water, and spray where you think the leak might get through.

It's a mechanic's trick

 

[DozerII]

If you're trying to find intake or vacuum leaks you can take a plastic one-use water bottle and poke a hole in the lid. Fill with water, and spray where you think the leak might get through.

It's a mechanic's trick

Ok, explain this to me a little more DUH, I understand the flammable aerosol as, if there is a leak the rpm increases, what happens with the water?[S

 

[05snopro440]

Ok, explain this to me a little more DUH, I understand the flammable aerosol as, if there is a leak the rpm increases, what happens with the water?[S

You'll notice it run rougher for a couple seconds.

 

[DozerII]

You'll notice it run rougher for a couple seconds.

Thanks 05, just the opposite of the flammable liquid and probably safer

 

[05snopro440]

Thanks 05, just the opposite of the flammable liquid and probably safer

Exactly!