Carb Problem

[aristellier]

Hi Guys, I recently changed my '63 dynamic from a 2bbl to a 4 bbl carb but I'm having a couple of problems. Firstly the carb had been rebuilt and was from a '63-'64 car so it should be ok. The problems are, 1, the engine will flood easily when cold but ok when hot and 2, if you accelerate hard from standstill the car dies until you back off the throttle but if you are already moving and stand on the throttle it's ok. Could it be wrong jets fitted? if so which ones should be fitted and how easy a job is it to do?
Thanks for any help
Aris

[J-(Chicago)]

I'd guess it's the float needs to be adjusted.

[Oldsguy]

The first problem would be a choke setting since it only appears when the engine is cold. Lean it out a little, or you don't have a sufficient gap set on the throttle plate. Even with the plate closed fully it really isn't, or shouldn't be. But I think that setting would effect your idle too so I vote for the choke setting. The second problem might be the accelerator pump, not sure about Rochester four jets (I think that is what you probably have) but on quadrajets the pump actuator lever has two holes in it to adjust the amount of plunger travel. The farthest hole out is a bigger squirt of fuel, the inside hole is a smaller squirt. The accelerator pump is on the driver's side front of the carb. You said the carb was rebuilt but I have found that those measurements can be off just a little and give a detrimental effect. At any rate it wouldn't hurt to double check them.

edit: And now I see whilst composing someone has posted succinctly before me. Could be float setting too.

[OLD SKL 69]

The first problem would be a choke setting since it only appears when the engine is cold. Lean it out a little, or you don't have a sufficient gap set on the throttle plate. Even with the plate closed fully it really isn't, or shouldn't be. But I think that setting would effect your idle too so I vote for the choke setting. The second problem might be the accelerator pump, not sure about Rochester four jets (I think that is what you probably have) but on quadrajets the pump actuator lever has two holes in it to adjust the amount of plunger travel. The farthest hole out is a bigger squirt of fuel, the inside hole is a smaller squirt. The accelerator pump is on the driver's side front of the carb. You said the carb was rebuilt but I have found that those measurements can be off just a little and give a detrimental effect. At any rate it wouldn't hurt to double check them.

x2

Also is it a 4GC or a quadrajet?

[aristellier]

4GC

[MN71W30]

I agree with the previous posts but you may want to consider changing to a newer quadra jet that have an adjustable flap over the top of the secondarys that slowly opens during hard acceleration to prevent a major bog. 780 vacume secondary Holleys have the same type of system. The old AFB carters are wide open and have a bog if you open the throttle fast from a stop. You probably have an old square 4 bbl. That is more primitive.
I bet if you were to hit the gas pedal half way then slowly floor it the car would work fine.
Give it a try.
Look for the Sherif first.

[aristellier]

Thanks for all the advice. Things are never quite as simple as they seem.

[joe_padavano]

Originally Posted by MN71W30

I agree with the previous posts but you may want to consider changing to a newer quadra jet that have an adjustable flap over the top of the secondarys that slowly opens during hard acceleration to prevent a major bog. 780 vacume secondary Holleys have the same type of system. The old AFB carters are wide open and have a bog if you open the throttle fast from a stop. You probably have an old square 4 bbl. That is more primitive.
I bet if you were to hit the gas pedal half way then slowly floor it the car would work fine.
Give it a try.
Look for the Sherif first.

A couple of problems with this info. First, the 63 will be a 394. There are no Qjet manifolds for the 394 and a spreadbore-to-square carb adapter will negate any flow improvements from the 4bbl.

Second, lots of carbs without secondary air valves work just fine. The issue isn't the design of the carb, it's the proper adjustment of the carb. Here's a link to a PDF version of a 1964 4GC manual that might help with adjustment:

http://oldcarmanualproject.com/manua...eMan/index.htm

Finally, the Qjet is not a vacuum secondary carb and Holley vacuum secondary carbs do not work the same way as the Qjet. Qjet secondary throttle plates are mechancally operated and will open anytime the throttle is mashed. The air valve above the throttle plates is actually operated by mass airflow - more airflow, larger opening. It's actually a pretty clever design, as the secondary fuel metering is a direct function of mass airflow, since the cam on the air valve shaft actuates the tapered secondary metering rods. This is a purely mechanical version of what some EFI systems do electronically.

Of course, none of that last paragraph is in any way related to the original question about a 4GC...

[MN71W30]

Thanks for cleaning up the post, I just figured people didn't need all the details.

[MN71W30]

Originally Posted by joe_padavano

A couple of problems with this info. First, the 63 will be a 394. There are no Qjet manifolds for the 394 and a spreadbore-to-square carb adapter will negate any flow improvements from the 4bbl.

Second, lots of carbs without secondary air valves work just fine. The issue isn't the design of the carb, it's the proper adjustment of the carb. Here's a link to a PDF version of a 1964 4GC manual that might help with adjustment:

I have had good luck using Quadrajets and a spacer on the older engines. To a purist it may not sound like a good idea and maybe not an option, but it works well. I have done it several times over the years. It isn't about max cfm flow. I don't think the 4GC's work just fine for the way I drive cars. They make good door stops.

[88 coupe]

Originally Posted by MN71W30

........ I don't think the 4GC's work just fine for the way I drive cars ........

How does the "way" one drives a car, make a carb work differently?

Norm

[88 coupe]

Originally Posted by aristellier

........ Firstly the carb had been rebuilt and was from a '63-'64 car so it should be ok ........

That is the assumption that gets many people into trouble. If it was rebuilt (and installed) properly you would not have started this thread.

Originally Posted by aristellier

........ Could it be wrong jets fitted? ........

If the carb came off a different engine, its possible, but not likely. Wrong jets could not cause the symptoms you described.

Originally Posted by aristellier

........ the engine will flood easily when cold but ok when hot ........

Too much choke? Fast idle too low?

Now, are you sure it is flooding, or is it going lean? When the engine is cold, it needs a richer mixture than at normal operating temperatures. Lean, at low RPM, could be a vacuum leak.

Not enough choke? Fast idle too low?

Originally Posted by aristellier

........ if you accelerate hard from standstill the car dies ........

If it died, you would have to restart it. Can we assume it "hesitates"? Is it less pronounced when it reaches operating temperature?

Originally Posted by aristellier

........ until you back off the throttle but if you are already moving and stand on the throttle it's ok ........

When it is cold or at normal operating temperatures? Are the symptoms different at higher speeds and/or different temps?

Norm

[aristellier]

Hi Norm, thanks for your input

1/ I purchased the carb from a carb specialist in the U.S and shipped it over, I presumed it would just need a bit of adjusting to get it right.

2/From coldI press the throttle once to activate the choke, it will turn over for several seconds before it starts to fire.The only way it will pick up is to use a bit more gas but if it doesn't catch it's flooded. Leave it half an hour and it will start right up. When warm it will usually start straight away.

3/I haven't tried to floor it when cold, when warm it will take off fine then after a second or two hesitate big time until you back off the throttle then it's ok. Once moving if you accelerate hard but smoothly all is fine.

4/ It seems to do it all the time but as I said I let it warm up a bit first. One thing I have noticed is that whenit is on choke the engine idles real smooth but once warm it's a little more lumpy.

[aristellier]

Ps. I had none of these problems before changing to this carb so I know everything esle is ok

[MN71W30]

Originally Posted by aristellier

2/From coldI press the throttle once to activate the choke, it will turn over for several seconds before it starts to fire.The only way it will pick up is to use a bit more gas but if it doesn't catch it's flooded. Leave it half an hour and it will start right up. When warm it will usually start straight away.

.

I suppose you tried different ways to start it cold but have you ever tried pumping the 2 or 3 times before starting it cold? Years ago, before fuel injection in the dead of winter in MN. Most cars had a certain way to start them when it was brutaly cold. It was a one shot deal before the battery died.
The good old days

[aristellier]

Yeah tried that! several pumps and still the same. I did notice something different today, I took the air cleaner off and looked down the carb to see how much fuel was going in and it took several pumps before fuel started to squirt in. Don't know if that has anything to do with my problem. Carbs are just alien to me.

[joe_padavano]

Originally Posted by aristellier

Yeah tried that! several pumps and still the same. I did notice something different today, I took the air cleaner off and looked down the carb to see how much fuel was going in and it took several pumps before fuel started to squirt in. Don't know if that has anything to do with my problem. Carbs are just alien to me.

Sounds like an accelerator pump problem, which would also cause the hesitation when you floor the gas. A "professional" rebuild is not always correct.

[MN71W30]

Originally Posted by joe_padavano

Sounds like an accelerator pump problem, which would also cause the hesitation when you floor the gas. A "professional" rebuild is not always correct.

X2,

[redoldsman]

I vote for the accelertor pump. If the carb stayed on the shelf for a long time, the leather on the pump could have dried out and shrunk. You should be able to take the top off the carb and spread the leather ring on the plunger out. The first thing I would do is take the air cleaner off and look down in the carb when you advance the throttle. You should see a good shot of gas inside the carb. If not, the pump is at least part of your problem.

[rocketraider]

It may not be carb related. Did you adjust all the throttle-to-transmission linkage when you changed to the 4GC carb?

4GC are also notorious for acting up if the wrong throttle plate to float bowl gasket is installed. Different applications use different vacuum and air bleed passages and using the wrong gasket can either block or open a passage that shouldn't be.

4GC have secondary air valves. They're buried in the secondary side of the carb float bowl and the airhorn must be removed for access.

[aristellier]

All linkage went pretty much in as it was once I got hold of the bellcrank pivot that goes on the carb.

[aristellier]

Thanks to you all for your input into my dilema