Quadrajet Making A Popping Sound

[c3po]

I took the El Camino out last night in 45 degree weather and she was making a popping sound until the car got totally warmed up.

The car did not do this last week when it was 72 degrees out.

I am going to have to start this car up cold and watch too see how fast the choke opens up and spray some carb cleaner to see if there are any vacuum leaks.

One guy told me that I could have an intake manifold vacuum leak and that when the car gets warm the metal expands and there is no leak.

Maybe I need to check my timing, but if it were off wouldn't the car be running bad all of the time.

My spark plugs need to be gapped at .045 and they might have been gapped to .050, I do not know if this would make a difference.

I believe my ignition coil is fine because the car starts perfectly whether the car is hot or cold.

Maybe I have the idle mixture screws too rich, which is letting more fuel into the combustion chambers and it is not getting burned.

A mechanic at the speed shop thinks its timing or my plugs are gapped to high meaning when cold the plugs are not firing right.

The other thought is that maybe the exhaust crossover in my intake manifold that brings heat to the carburetor is stopped up, obviously when the car is cold it needs the heat for a better burn as opposed to when it is warmer outside.

I am going to do the mixture screws again and turn them all the way in and then 1-1/2 turn out or maybe 2 turns out, I checked them last night and they are at 4.5 turns out.

I do not think I have a burnt valve or a weak spring in the cylinder heads because the car runs great when she is warmed up.

If I cannot figure it out I may get my friend who is pretty good with working on engines.

 

[oilboy123]

Is it possible the carb is running lean because of the choke setting until it's warmed up?

 

[c3po]

So maybe I will have to play with the choke setting, there is a screw that sets how fast the choke opens up.

 

[oldmaninsc]

Another thing. Many of the carb. vehicles had a "slinky" type hose that runs from the exhaust manifold to the air filter assembly.
Under cold conditions is suppose to draw warm air off the exhaust manifold to help with cold drivability problems.

 

[c3po]

Originally Posted By: oldmaninsc
Another thing. Many of the carb. vehicles had a "slinky" type hose that runs from the exhaust manifold to the air filter assembly.
Under cold conditions is suppose to draw warm air off the exhaust manifold to help with cold drivability problems.

Unfortunately I put headers on the car and an aftermarket air cleaner assembly. I took the original air cleaner assembly off years ago and the hose that ran from the exhaust manifold to the air cleaner was causing problems since the door in the tube was staying closed.

It was great for warm startup's but once the car was warmed up I hardly had any power.

 

[demarpaint]

If you had good vacuum as you mentioned the other day, then I'd rule the intake manifold leak out. That is assuming you checked the vacuum with the engine at operating temperature. If you didn't then check it when the engine is at operating temps and make sure you still have good vacuum.

My bet is the choke is still probably out of adjustment. As I mentioned in the past they can be a real PIA to set up, but once its dialed in it should not require any more adjustments.

Good luck and keep me informed!

Frank

 

[JetStar]

Sounds like the choke is out of adj. Does it have the coil type mounted on the carb, or the coil mounted on the intake. Sounds like it needs to be adjusted to close the choke a bit. while you are adjusting that, make sure your vacuum pull-offs are adjusted right to prevent over choking. Stock or aftermarket intake manifold? Aftermarkets usually dont have an exhaust cross-over in them. 4.5 turns out on the idle mixture seems like a lot.

 

[oldmaninsc]

Originally Posted By: c3po
Originally Posted By: oldmaninsc
Another thing. Many of the carb. vehicles had a "slinky" type hose that runs from the exhaust manifold to the air filter assembly.
Under cold conditions is suppose to draw warm air off the exhaust manifold to help with cold drivability problems.

Unfortunately I put headers on the car and an aftermarket air cleaner assembly. I took the original air cleaner assembly off years ago and the hose that ran from the exhaust manifold to the air cleaner was causing problems since the door in the tube was staying closed.

It was great for warm startup's but once the car was warmed up I hardly had any power.


I see - makes sense.

Then it does sound like it could be a choke problem.
This is one of the things I don't miss! When I lived in the midwest - it could be a real pain getting the chokes on some cars to function right. Staying closed long enough to not have drivability problems, but not staying closed too long once the engine is warmed up.

 

[c3po]

Originally Posted By: JetStar
Sounds like the choke is out of adj. Does it have the coil type mounted on the carb, or the coil mounted on the intake. Sounds like it needs to be adjusted to close the choke a bit. while you are adjusting that, make sure your vacuum pull-offs are adjusted right to prevent over choking. Stock or aftermarket intake manifold? Aftermarkets usually dont have an exhaust cross-over in them. 4.5 turns out on the idle mixture seems like a lot.


I readjusted the choke so it stays on longer, I will start it up tommorow and see how it goes. I have the Edelbrock 2101 intake manifold that does have the exhaust crossover.

I turned the screws 2 turns out from seated, so I will see what happens. If this choke opens up too quickly I will get another one and have my friend who is good at this help me put it on, or I will probably watch him.

 

[Muffy]

sounds like the motor is real thirsty when cold and a worn out accelerator pump in the carburetor is at fault. this will be more noticeable when cold as it needs more fuel. it causes a lean condition momentary and it will starve. when the engine is warmed up it does not need as much as fuel and may not be obvious. this condition described may be under acceleration.

 

[c3po]

Originally Posted By: Muffy
sounds like the motor is real thirsty when cold and a worn out accelerator pump in the carburetor is at fault. this will be more noticeable when cold as it needs more fuel. it causes a lean condition momentary and it will starve. when the engine is warmed up it does not need as much as fuel and may not be obvious. this condition described may be under acceleration.


I checked the accelerator pump and it was squirting out fine, the carburetor is only 3 years old. The car accelerates fine when it is warmed up, is there a correct way to check the condition of the accelerator pump. I moved the carburetor just like it would move when the gas peddle was used and the accelerator pump squirted out fuel.

 

[demarpaint]

It could be the accererator pump, squirting out fuel means its working, the amount of fuel needed to run the engine under load is another story. I'm not sure how to measure the volume of fuel you need, but you've been having problems with this carb for a while, and have been making a lot of adjustments, so if you can't get it dialed in you might have to look for other issues.

As I've mentioned and others have, they can be a pain in the butt to set up. Sometimes when you can't get them set up properly the carb could be bad or in need of a rebuild. I've seen them fail in very short order, so the fact that it's only 3 years old doesn't mean much. I've also seen them messed up in handling. If a carb is turned over and shaken it can mess things up, that sometimes happens in shipping, they're very fussy at times. Keep at it, but if you can't get it dialed in, consider rebuilding it.

 

[c3po]

I have a feeling that the spring in the choke may not be working right, if this is the case then I will need to contact Sean Murphy and give him my carburetor number and have him send me a choke that matches up.

The mechanic at Chevrolet put on a new choke that he had at his house, maybe it is not the right match for my carburetor.

It is going to be a sunny day tommorow so I will take the car out and see how it goes.

 

[mechtech2]

Lean or retarded ignition timing.

 

[c3po]

Originally Posted By: mechtech2
Lean or retarded ignition timing.


I was leaning towards this too, but I only have the problem when the engine is cold, if the timing was off then wouldn't I have this problem when the engine is warmed up too.

 

[flanso]

Choke coils are bimetal, two different metal alloys bonded together. Each metal has a different rate of expansion. They are designed to give a certain angular degree of deflection per degree of change in temperature. There are many different ones; each is designed for a specific carburetor calibration. If the choke coil you are using came from a different carb than the one on your car, that is likely to be the problem.

 

[c502cid]

As long as everyone is internet guessing, I'm going to throw my hat in the ring. It's a bad valve, probably exhaust.

 

[demarpaint]

Vacuum checked out OK, I would now consider running a compression check and post some readings. Even if you ran a check a month or so ago I would run it again. There will be some time before the proper choke spring comes in. A compression test certainly won't hurt and will rule out bad rings/valves.

If the rings valves check out OK with a compression test, and the new spring doesn't work, rebuild the carb.

I have a feeling its not the choke spring that's the problem here, because they can be adjusted.

Good point, since we are not seeing the car in action we are internet guessing.

 

[mechtech2]

Cold engines need a richer mixture and more ignition advance.
I also hope you have the heat passage in the manifold open and not blocked.

 

[c3po]

Originally Posted By: mechtech2
Cold engines need a richer mixture and more ignition advance.
I also hope you have the heat passage in the manifold open and not blocked.


I know this is driving everybody including myself nuts.
Someone told me the way to check to make sure the exhaust heat passage is not clogged is too take the plate off on the manifold where the hot air choke would be equipped.

Since I do not have a hot air choke this is blocked off, if I start the car with this plate off and air blows out then this is clear.

I have also read that the accelerator pump is needed more on startup and when you 1st get going.

I got a can of carb cleaner and I will check for any more vacuum leaks.

I was also able to turn the choke a little bit more counterclockwise, so I will see how things go tommorow.

If it does not run any better then I will have to take it to this speed shop where I know this guy and have him:

1) Check timing
2) Check accelerator pump
3) Do a Compression Test

Tommorow afternoon is going to be sunny and nice out, so I will get on this and stop dragging my feet.