I have this carb on a 425 Nailhead. If I let the car set for more than a couple days, I have to pump the heck out of the gas pedal to get it to finally fire. The longer it sets the more I have to pump; up to thirty times. It is like the gas has drained from the carb. I had heard somewhere that there could be an unused port or hole that should be filled with silicone caulk in certain applications. I have the carb off right now, doing some other work on the engine. Can anyone help me out with suggestions?
Carter AFB 4bl Carb.
- Thread starter conroy
- Start date
Most all AFB's have done that since the day they were new. Way back when the cars were new, or fairly new, we used them most every day. Now since they have become our play toys, mostly, they sit around for days, weeks, months at a time between uses. This is nothing new. My '64 Riv. has done it since the day I bought it in '64. To the dismay of some I installed a Holley DP some 30+ yeras ago & even after sitting for 3 months it starts after a couple pumps. Of course I use an accumulator to pump oil pressure into it before starting.
Tom T.
Tom T.
lowvoltage
Member
Carb leakage.
You were correct. The fuel remaining in the carb bowl is disappearing. It is a common oroblem, and not too difficult to correct, The problem is the well jets are leaking. If you remove the carb, remove any remaining fuel by inverting over a container. Dis-assemble the carb, there are three main sections: Top or cover, center section and base. The leak occurs at the two aluminum rivets visible on the underside of the center section, when it is assembled to the base this section is in a depression in the base. An overhaul kit will give you a soft filler (like a sponge) that rests in this depression to seal off any leakage. It does not work. Use an epoxy (fuel resistant) and make a coating to cover the underside of the rivet section, use care and remember the base and center section must fit properly, it is not a difficult procedure. Before applying the epoxy eyeball the parts, you will see what I am talking about. It is not a great idea to allow this leakage to continue, it is flooding the manifold and cylinders whenever you stop the engine. After this repair is completed, the startup is fine. Be safe and enjoy.
You were correct. The fuel remaining in the carb bowl is disappearing. It is a common oroblem, and not too difficult to correct, The problem is the well jets are leaking. If you remove the carb, remove any remaining fuel by inverting over a container. Dis-assemble the carb, there are three main sections: Top or cover, center section and base. The leak occurs at the two aluminum rivets visible on the underside of the center section, when it is assembled to the base this section is in a depression in the base. An overhaul kit will give you a soft filler (like a sponge) that rests in this depression to seal off any leakage. It does not work. Use an epoxy (fuel resistant) and make a coating to cover the underside of the rivet section, use care and remember the base and center section must fit properly, it is not a difficult procedure. Before applying the epoxy eyeball the parts, you will see what I am talking about. It is not a great idea to allow this leakage to continue, it is flooding the manifold and cylinders whenever you stop the engine. After this repair is completed, the startup is fine. Be safe and enjoy.
4speed said:
4speed, I have never smelled gas. That is why I have always thought the engine was starved for gas rather than flooded. My friend suggested that if the choke was stuck open it could take that many pumps to compensate. Frankly it seemed to me since the number of pumps increased with the length of time it sat idle, it indicated it was a problem with gas slowly escaping the bowl. This is a good conversation, but with conflicting opinions. Anyone have a tie breaker?
travelingmike1
Member
Silicone and Gasoline don't mix!
In reference to using silicone to plug a carb passage, Don't Do It! Silicone sealers turn to jelly in the presence of gasoline. If you need to plug a passage or seal an existing plug, use epoxy. Check the label for compatability, and I recommend testing a small amount of the epoxy. Mix up a bit of it and allow it to cure well, then soak the sample in a small amount of gas and allow it set over night. If there is any reaction or break down, try a different sealer.
In reference to using silicone to plug a carb passage, Don't Do It! Silicone sealers turn to jelly in the presence of gasoline. If you need to plug a passage or seal an existing plug, use epoxy. Check the label for compatability, and I recommend testing a small amount of the epoxy. Mix up a bit of it and allow it to cure well, then soak the sample in a small amount of gas and allow it set over night. If there is any reaction or break down, try a different sealer.
Here' another one. When the car is running, shut it down. Pull the air cleaner and look down the throttle bore, work your throttle linkage and have a look at the squirt you get from the accelerator pump to familiarize yourself with it. Note the position of the choke, it should be wide open.
Now when the car has sat, before touching anything, pull the air cleaner and do the same thing. Now you may have somewhere to start.
:thumbsup:
Now when the car has sat, before touching anything, pull the air cleaner and do the same thing. Now you may have somewhere to start.
:thumbsup:
Since I have the intake manifold and carb off of the car and do not expect to have it back together for a while, I cannot check the choke operation out at this time. Reading all the replies, I have decided to pull the top of the carb off and check for leakage from the bowl as jassbass suggested. It seems like the least invasive thing I can do just to conirm or eliminate a problem. Besides, it will be an opportunity to learn more about it. We'll take one step at a time and see where it leads. Please jump in if there are any more ideas. Thanks to everyone for the suggestions.
lowvoltage
Member
Let me get back on track,it's a Carter AFB not a quad.
Is this problem a new occurance, was it ok before? When it is running is the acceleration normal or does the engine stumble. Is this a recent purchase or have you owned the car for some time and is it a regular daily or weekly runner. As a suggestion, you said the manifold and carb were now off the car, remove the carb from the manifold. remove the inlet fuel filter and fill the carb with fuel. As the previous note said with the choke plates open look down the carb intake and see if the fuel is squirting on each opening of the throttle, without this squirt you will have a bear of time starting. The accelerator pump is the unit that gives this squirt, it has a habit of shrinking in it's bore and does not build up pressure enough to squirt out starting fuel. With this carb I would be surprised if you said you were getting a good pump squirt. With no pump squirt it could be your whole problem. You said you could not check the choke beceause the garb was off the car, you are only interested in the closing action of the choke plates. This action is visible off or on the car. The choke cover bimetal spring closes the plates. When you rotate the throttle lever the choke plates should close, the colder the cover the stronger the choke closing will be. Enough words, get us some results. Use caution with gasoline, it's not a play liquid. This work should be done outside. Good luck.
Is this problem a new occurance, was it ok before? When it is running is the acceleration normal or does the engine stumble. Is this a recent purchase or have you owned the car for some time and is it a regular daily or weekly runner. As a suggestion, you said the manifold and carb were now off the car, remove the carb from the manifold. remove the inlet fuel filter and fill the carb with fuel. As the previous note said with the choke plates open look down the carb intake and see if the fuel is squirting on each opening of the throttle, without this squirt you will have a bear of time starting. The accelerator pump is the unit that gives this squirt, it has a habit of shrinking in it's bore and does not build up pressure enough to squirt out starting fuel. With this carb I would be surprised if you said you were getting a good pump squirt. With no pump squirt it could be your whole problem. You said you could not check the choke beceause the garb was off the car, you are only interested in the closing action of the choke plates. This action is visible off or on the car. The choke cover bimetal spring closes the plates. When you rotate the throttle lever the choke plates should close, the colder the cover the stronger the choke closing will be. Enough words, get us some results. Use caution with gasoline, it's not a play liquid. This work should be done outside. Good luck.
I have owned the car for four years. This has been a problem from day one for me. I drive the car at least once a week, April through October (roughly). Once started and warmed up for a couple minutes, it runs fine. If I put it in gear immediately upon starting it will stall, but other than that, it runs fine after a little warming. I will get into it this weekend and let you know my results. Thanks.
I have removed the top of the carb and filled the bowls with gas. I have covered the bowls to eliminate evaporation. I will check it tomorrow and on subsequent days to see if the gas is leaking through. I noticed the shaft for the accelerator pump is extremely loose in the opening it passes through on the top section. I mean really loose. Is it supposed to be that way or is there supposed to be a seal? It seems like an awful lot of evaporation could happen with such a gapping space.
lowvoltage
Member
That is normal. What about the squirt when you rotate the throttle lever, there should be a good stream from the nozzles into both carb throats. The carb reservoir is already vented to the atmosphere so evaporation is normal in that vintage. Sealed systems came later.
I did not actually plan on working on the carb right now. I have another thread going about nailhead lifter noise. I started digging into that problem and after I had the manifold removed with the carb, I started getting curious about the carb in between working on the lifter noise. Although I know I am at a disadvantage with the carb off and no way to fully test it, I thought I would take the opportunity to look into it.
Tonight I checked the gas level in the bowls. The gas in the bowl that houses the accelerator pump was significantly lower the the other bowl. Am I to assume this indicates unacceptable leakage? I believe I eliminated any chance of evaporation. I disassembled most components of the carb. It actually looked pretty clean but I cleaned it as I went. There were a few things I noted. The diaphram on the end of the accelerator pump looks a little mishapen and worse for wear. The screw that mounts the pivot for the pump lever was frozen. Since I could not remove it (PB Blasted it for overnight), I wonder if it has been passed over in a rebuild. The orfice in the bottom of the bowl and nearest the accelerator pump has a check valve in it. Could this pose any problem? I cleaned the choke out, it was carboned up a little. Since I had never had a choke apart, I just jumped right in. Now I will have to refer to my manual to put it back together properly. Although obvious now, it never occured to me that the choke housing could be adjustable by loosening the screws and rotating it. I am not sure I have it adjusted correctly now but I will work on that tomorrow. I forgot to check the squirt tonight. I will do that tomorrow. Other than the low level of gas in the one bowl, and a suspicious accelerator pump, I did not see anything obvious to blame the hard starting on.
Tonight I checked the gas level in the bowls. The gas in the bowl that houses the accelerator pump was significantly lower the the other bowl. Am I to assume this indicates unacceptable leakage? I believe I eliminated any chance of evaporation. I disassembled most components of the carb. It actually looked pretty clean but I cleaned it as I went. There were a few things I noted. The diaphram on the end of the accelerator pump looks a little mishapen and worse for wear. The screw that mounts the pivot for the pump lever was frozen. Since I could not remove it (PB Blasted it for overnight), I wonder if it has been passed over in a rebuild. The orfice in the bottom of the bowl and nearest the accelerator pump has a check valve in it. Could this pose any problem? I cleaned the choke out, it was carboned up a little. Since I had never had a choke apart, I just jumped right in. Now I will have to refer to my manual to put it back together properly. Although obvious now, it never occured to me that the choke housing could be adjustable by loosening the screws and rotating it. I am not sure I have it adjusted correctly now but I will work on that tomorrow. I forgot to check the squirt tonight. I will do that tomorrow. Other than the low level of gas in the one bowl, and a suspicious accelerator pump, I did not see anything obvious to blame the hard starting on.
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lowvoltage
Member
You are making good progress. The acc pump should be replaced. The level of fuel in the pump chamber should reflect the level in the float chamber. The check ball in the bottom off the chamber should allow fuel to enter the chamber but seal off the fuel from returning back into the float chamber during the downward stroke, it should exit up to the outlet nozzles and into the throats of the carb below the choke plates. With the cover of the carb off, take the acc pump off the cover and put some fuel in the float bowl, fuel should enter the pump chamber, put the pump slowly into its chamber and you will see the action of the fuel. If when you push the pump down the fuel does not come up to the nozzles, and in your case with the cover off it may be very easily seen there is a problem.. Prior work may have created problems. I have seen check balls left out, gaskets reversed closing off ports, springs left out, many errors. If memory serves me, there should be a spring in the pump itself, and another in the pump chamber below the pump. I'll not pester you, enjoy the work.
Lowvoltage, you are not pestering me. Since the weather has turned cold, I am concentrating on painting several components I have removed from the motor, inside. In between coats I am woking on the carb. The PB Blaster broke loose the screw holding the acc pump. Once removed I noticed the plunger shaft is bent. The diaphram on the pump is definitely shot, also. I will be ordering a new pump. In your opinion what is the most likely cause of the bent shaft? I noticed there are three locations where the "s" pin that connects the arm to the top of the plunger. If it is located in the wrong hole, can that bind and bend the shaft? I appreciate all your help.
lowvoltage
Member
I've never seen a bent pump shaft. When you get ready to reassemble don't put the "S" connector on till the cover is in place and the pump is in the chamber. That way you can be sure the pump is not binding. The different holes may be for shorter or longer pump stroke, if the book does not recommend the correct hole for your engine, make it the longest without bottoming or binding.It sounds like you are on the right track.
X
XXX82
Guest
Afb
From your description (cold driveability) your problem is mostly choke.
Also check your gas cap vent, and here's some other things to think about. the bore for the may be enlarged the cup should give a little drag when installed less than an oz if the pump bore you can mix and match parts take the cup from one and put it on the AFB stem also the check ball may need to be reseated do this after cleaning.
Remove the ball inspect the seat your overhaul kit should have a new ball replace the old ball and tap it with a nail NOT brass to reform the seat this is a GM approve method would you believe
When the laws changed for car crash/rollover GM carbs had a rubber check valve in the fuel filter to prevent leaks, it helped the drain back problem to
From your description (cold driveability) your problem is mostly choke.
Also check your gas cap vent, and here's some other things to think about. the bore for the may be enlarged the cup should give a little drag when installed less than an oz if the pump bore you can mix and match parts take the cup from one and put it on the AFB stem also the check ball may need to be reseated do this after cleaning.
Remove the ball inspect the seat your overhaul kit should have a new ball replace the old ball and tap it with a nail NOT brass to reform the seat this is a GM approve method would you believe
When the laws changed for car crash/rollover GM carbs had a rubber check valve in the fuel filter to prevent leaks, it helped the drain back problem to