Carb Problem
#1
Carb Problem
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
Thanks for any help
Aris
#3
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.
edit: And now I see whilst composing someone has posted succinctly before me. Could be float setting too.
#4
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.
Also is it a 4GC or a quadrajet?
#6
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.
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.
#8
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.
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.
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...
Last edited by joe_padavano; February 18th, 2009 at 04:16 PM. Reason: Spelling
#10
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:
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:
#12
If the carb came off a different engine, its possible, but not likely. Wrong jets could not cause the symptoms you described.
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?
Norm
#13
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.
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.
#15
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.
.
.
The good old days
#16
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.
#17
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.
#18
#19
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.
#20
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.
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.
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