Rochester 2GC Bowl Overflow Problem

[Machine Gun]

My Rochester 2GC has a history of occasionally vomiting fuel out the bowl vent immediately after starting the car. It happens only after the car has been sitting for a week or more, and has never done it when the car is in more frequent use. When the car starts it begins to run very rough, which tells me that things are going south under the hood. I shut the engine down, mop up the fuel, and by the time I'm done cleaning it up I can start the car, and all will be normal until the next time I let the car sit. It's done this ever since I bought the car nearly seven years ago.

 

I rebuilt the carburetor myself shortly after buying the car. During the rebuild I replaced the needle and seat from the kit and set the float height. Things improved, but the problem didn't completely go away. I decided that a professional should service the carb, so I sent it to a guy on LI two years ago who did a wonderful job rebuilding it. The carb worked flawlessly in every respect for the past two years, except that now the overflow condition returned.

 

Dirt that may clog the needle and seat? Why then only after the car sits for awhile and not at other times? Stuck float? Again, why only after sitting for awhile? Any ideas before I open things up?

[EmTee]

My guess: the fuel boils out of the bowl after shutdown (engine is hot).  If like my cars, the bowl needs to be refilled by either priming with the electric pump ('38) or a couple of 10~15 second cranking sessions before firing up.  Anyway, what I think might be happening is the float occasionally gets stuck down, holding the needle open.  Once the car starts, the vibration and (over)full bowl gets the float unstuck.  I'd remove the top of the carb, suck out the fuel from the bowl and check what happens when the float is hanging free.  If my hunch is correct, you may feel something interfering with smooth operation of the float when coming off the low stop.  It might be something to do with the needle causing it to stick, but I'll bet you find something that feels like a 'notch' just as the float starts to come up...

[carbking]

I read that you set the float height; did you also set the float drop?

 

Also, are you using an original style fuel valve with a neoprene pointed valve, or something else?

 

Jon.

[JohnD1956]

The following is all theory, not based on any evidence, except it seems  to work well.

Do you put your car inside when returning from a run?  If so, since the carbs vent to the atmosphere, it may be that the bowl empties out leaving the needle valve open upon the next use. 

Then, if you have been using an ethanol blended fuel it may be that the needle gets stuck till it soaks in fuel again. 

While I always use non ethanol "recreational " fuel (readilly available in my area) I usually leave my cars outside at least 20 minutes or more, with the hood open, after any run. In my experience this allows:

vapors to vent outside the garage. The engine to partially cool off preventing further fuel bowl perculation.

Refilling the fuel bowl when re-starting the car to put it inside. 

 

 

 

 

[Machine Gun]

22 hours ago, EmTee said:

My guess: the fuel boils out of the bowl after shutdown (engine is hot).  If like my cars, the bowl needs to be refilled by either priming with the electric pump ('38) or a couple of 10~15 second cranking sessions before firing up.  Anyway, what I think might be happening is the float occasionally gets stuck down, holding the needle open.  Once the car starts, the vibration and (over)full bowl gets the float unstuck.  I'd remove the top of the carb, suck out the fuel from the bowl and check what happens when the float is hanging free.  If my hunch is correct, you may feel something interfering with smooth operation of the float when coming off the low stop.  It might be something to do with the needle causing it to stick, but I'll bet you find something that feels like a 'notch' just as the float starts to come up...

I'm sure the bowl is dry after several days due to the length of time the car cranks before it fires. It'll fire right up after sitting for only a few days. I'll check the float action when I open up the carb, good suggestion.

 

22 hours ago, carbking said:

I read that you set the float height; did you also set the float drop?

 

Also, are you using an original style fuel valve with a neoprene pointed valve, or something else?

I did set the float drop when I did my own rebuild. I can only trust that the rebuilder who did the carb two years ago checked it as part of his routine. Don't forget, it was all good for two years until a month ago. As for the neoprene-tipped valve, I don't know what the rebuilder used, but the kit I installed back when I first got the car was one I purchased from you and therefore would have had the proper components. I sent the carb out for a rebuild two years ago because I figured there are subtleties to rebuilding a carburetor that aren't in my knowledge base.

 

21 hours ago, JohnD1956 said:

Do you put your car inside when returning from a run?

Yes, most times the car goes right back in the garage. Unfortunately non-ethanol fuel isn't available anywhere near where I live so I won't be able to easily experiment with it, but I expect that the main (only?) difference the fuel would make is how quickly the it would evaporate after sitting for several days. Regardless of how I cool down the car before putting it to bed I'm still going to start with a dry bowl after many days of sitting.

 

Time permitting this week I'll open up the carb and have a look-see inside to see what I can figure out. If nothing obvious presents itself upon opening it, I'll let the components dry out in the open and then see how freely the float and needle valve move.

[carbking]

GUESSING:

 

Today's fuel, when it evaporates, leaves a residue similar to glue.

 

But the fuel is also an excellent solvent.

 

So possibly when the vehicle sits for long periods of time, and the float is allowed to drop completely, that there is enough residue on the float hanger to keep it down, and the bowl overflow. Once new fuel is in the bowl, the "glue" is dissolved, and everything works again.

 

Probable solution is to remove the carburetor, and simply wash all of the residue out of the bowl area, then reassemble.

 

Of course, the more obvious, and easier solution, plus more fun, is drive the vehicle more often  

 

Jon. 

Edited June 26, 2022 by carbking (see edit history)

[60FlatTop]

Odd things can happen on a 60 year old car. A random thought is that the fuel pump internal pressure control may not be reacting properly to those dry starts. There is a spring attached to the diaphragm and pump arm to control that. Either could be amiss. You could Tee off a fuel pressure gauge to check it if you can catch the event or just put a new fuel pump on in the same amount of time. In the same situation I would put a new fuel pump on. If I was wrong I would have a spare.

 

I am a supporter of the frequent drives. Also, I am not a gas price shopper. Everything I have gets Mobil regular, high test if required. It is considered a premium blend and usually costs more but I haven't experienced the problems others have.

[EmTee]

6 minutes ago, 60FlatTop said:

Everything I have gets Mobil regular, high test if required. It is considered a premium blend and usually costs more but I haven't experienced the problems others have.

Pay now or pay later...

https://www.consumerreports.org/fuel-economy-efficiency/top-tier-gasoline-worth-the-extra-price-a7682471234/

 

[Machine Gun]

@carbking Very interesting about fuel residue, I didn't know that was a thing. I'll let you know what I find after I open up the carb.

 

@60FlatTop I do have a new spare fuel pump I keep in the trunk. I'll take your suggestion and swap it out if all else fails.

 

[BRB62]

I have a similar issue with the 4GC in my Electra. Apparently what happens is that the secondary needle catches on a slight notch that has worn over the years. What I found was that if the car sits for too long the fuel dries up/drains from the carby and I tend to pump the accelerator more to get fuel up for the car to start. This sets the secondaries into the "sticking" position and the carby gets full fuel, flooding and bogging the engine down. The first (many) times this happened I had to remove and de-carbon the spark plugs each time. The car does the same as you describe, it starts and seems fine but the idle gets gets rougher and rougher very quickly and fuel pumps out of every part of the carby if I don't stop it in time. Not pretty.

I have had the carby looked at professionally but they were unable to entirely remove the notch. I am now very careful when pumping the accelerator on startup and I have a large screwdriver handy to tap the area where the secondary needle sits to dislodge it if it gets stuck. This works. I find if the secondaries open in normal highway driving I on't have a problem but definitely is a lot worse when the car sits for a while. It is possible that you may have a similar issue with a sticky needle & seat? I am not a mechanic so my technical terms may be astray but this is the information given to me by the person who rebuilt it. 

[Frank DuVal]

On 6/26/2022 at 8:49 AM, 60FlatTop said:

A random thought is that the fuel pump internal pressure control may not be reacting properly to those dry starts.

The only pressure control in the fuel pump is the spring. The cam lobe pushes up on the rod/lever/whatever and compresses the spring. In doing so the check valve A allows the diaphragm to suck fuel from the tank into the pump chamber. The spring pushes on the diaphragm rod to force that fuel through check valve B and out to the carburetor(s). If the carburetor(s) need no fuel, the diaphragm does not move and the spring stays compressed. Every rotation of the cam (crankshaft in the case of Corvair engines) pushes on the rod/lever/whatever, repeating the suck fuel from the tank on the push, if there is room in the pump chamber for it, and the spring tries to push the diaphragm in the opposite direction to push fuel to the carburetor(s)..

 

If a check valve sticks open, fuel pressure is lower. It either leaks back into the tank or stays in the pump chamber.

 

Trust me that Corvair people fully understand how that simple AC fuel pump designed in 1929(?) works, since most every pump for us made in the last 10 years + has too strong a spring and makes 7 psi or so, which overwhelms the needle/seat and causes flooding. Using the spring from the old pump fixes it. One Corvair owner even markets a spacer to allow shimming the spring to proper pressure output. Here is a video of the inside of the AC style pump, does not mater if yours is lever driven or whatever, the operating principle is the same.

 

 

 

http://corvaircenter.com/phorum/read.php?1,1072514,page=1

 

Way back in Skinned Knuckles magazine was a great article written by John Moody of DC. It explained the history of the AC fuel pump and how it worked. The website is now gone, along with the magazine, so except for the copies not yet recycled, gone forever that information.

[60FlatTop]

When the needle valve closes the diaphragm stays in its lowest position and stops pumping unless one believes something could go wrong. I certainly know what "trust me" means. It's a Yiddish term isn't it?

[Bloo]

14 hours ago, BRB62 said:

Apparently what happens is that the secondary needle catches on a slight notch that has worn over the years.

Do you mean a groove where the needle contacts the seat? If the needle has a groove in it, it is shot. You would need a new needle and seat.

 

14 hours ago, BRB62 said:

This sets the secondaries into the "sticking" position and the carby gets full fuel, flooding and bogging the engine down.

I'm not sure I understand. If there is a "sticking position" for the float itself, something is not set up right about the float. The float drop setting probably.

 

7 hours ago, Frank DuVal said:

The only pressure control in the fuel pump is the spring. The cam lobe pushes up on the rod/lever/whatever and compresses the spring. In doing so the check valve A allows the diaphragm to suck fuel from the tank into the pump chamber. The spring pushes on the diaphragm rod to force that fuel through check valve B and out to the carburetor(s). If the carburetor(s) need no fuel, the diaphragm does not move and the spring stays compressed. Every rotation of the cam (crankshaft in the case of Corvair engines) pushes on the rod/lever/whatever, repeating the suck fuel from the tank on the push, if there is room in the pump chamber for it, and the spring tries to push the diaphragm in the opposite direction to push fuel to the carburetor(s)..

Spot on. An afternoon spent nitpicking that function, especially the function of the check valves and the fuel pressure, is worth about 10 electric fuel pumps.

 

7 hours ago, Frank DuVal said:

Trust me that Corvair people fully understand how that simple AC fuel pump designed in 1929(?) works, since most every pump for us made in the last 10 years + has too strong a spring and makes 7 psi or so, which overwhelms the needle/seat and causes flooding.

This is something that was never checked in the old days, except by guys like me on extreme "tough dog" cars, because it was almost never wrong. The fuel pressure specs were in the old Motor and Chilton manuals. The problem with some newer pumps sure isn't limited to Corvairs. I have seen it on crimped pumps on other cars where you can't do anything about it. The Corvair subject always comes up because the Corvair people realize it is happening and almost no one else does. The float valve in the carb and the diaphragm spring in the fuel pump are fighting each other. If the fuel pressure is wrong the float level becomes wrong as a result. If the float level is wrong the mixture is also wrong, even if the carb doesn't run over.

 

Edited June 28, 2022 by Bloo (see edit history)

[BRB62]

As I mentioned, I am not a mechanic and am only stating what I remember from a number of years ago. It is just as likely that I have it wrong. My main point is that my car demonstrates the same symptoms, flooding over when first started after a period of not being used.

Having driven carburetor cars for a long time, I used to give the accelerator pedal a couple of pumps prior to starting, just habit. I have found with my Electra that I have to be more gentle with this action, or not at all, to prevent the carby from flooding. For this first start after a break I take off the air cleaner, start the car and check that the secondary side is dry (no fuel). If it is wet I stop the engine, give the back of the carby a "tap" to reset whatever it is that has stuck, dry out the excess fuel inside and try again. I only have to do this once and almost never when the car is used more often. It does not happen every time. I also would love to know what it is that I am resetting when I tap the carby. Perhaps it is the float that sticks?

[Bloo]

It's possible it could be sticking on the pin. Whatever it is I hope you can get it sorted. All the best.

 

 

[Machine Gun]

My carb is now open and sitting on the bench with the air horn assembly sitting horizontally with the float hanging down just at it does when installed on the car. I'm going to leave it alone for at least ten days to ensure that it's completely dry, and then I'll have a look to see if I uncover any clues. Stay tuned.

[carbking]

Measure:

 

(A) the distance from the air horn gasket to the extreme bottom of the float

(B) the distance from the top of the bowl casting to the floor of the bowl in the area where the lowest point of the float would be

 

Compare - A should be less than B by at least 1/16 inch, preferably 1/8 inch.

 

Also, once you have allowed everything to dry out, and have tested the above, and for the components being sticky, check to see what valve was used by the mechanic that rebuild it for you.

 

One other possible issue that has already been touched in this thread. I was taught by my mentor (Carter Carburetor School headmaster) that when installing a carburetor on an engine, THE FUEL BOWL SHOULD BE FILLED PRIOR TO CRANKING THE ENGINE!

 

Why?

 

With no residual pressure, the fuel pump diaphragm will flex approximately 1/16 of an inch more than normal; releasing any dried fuel residue from the diaphragm, and sending it up line to the carburetor. Possibly, some residue could be getting into the fuel valve area preventing it from completely closing until the residue washed out.

 

Generally, listening to folks that were in the business is a good idea.

 

Jon.

[Frank DuVal]

23 hours ago, 60FlatTop said:

When the needle valve closes the diaphragm stays in its lowest position and stops pumping unless one believes something could go wrong.

Depends on fuel pump position, on Corvairs the diaphragm stays in the up position against spring pressure, diaphragm is below spring.😉 Same on small block Chevy, diaphragm below spring. This way the diaphragm is spring loaded and ready to flow fuel to the carburetor(s) as soon as the needle opens.

 

5 hours ago, carbking said:

THE FUEL BOWL SHOULD BE FILLED PRIOR TO CRANKING THE ENGINE!

Sounds like good advice. But, have any idea how to accomplish this cleanly? Both on a rebuild (put fuel in before assembling top? Seems hard to assemble linkage on the side, and not practical for those kitchen table assembling times of our youth) and after the car sits for a few weeks? Well, electric pump comes to mind, but I thought we were trying not to use those. I can tell you a Rochester H/HV has either a duckbill or two small holes to try to put gas into. You use a chemical wash bottle?

[Frank DuVal]

On 6/27/2022 at 3:56 PM, 60FlatTop said:

I certainly know what "trust me" means. It's a Yiddish term isn't it?

NO. 

[Machine Gun]

14 minutes ago, Frank DuVal said:

NO. 

That seems to have gone over like a fart in church.

[carbking]

1 hour ago, Frank DuVal said:

Depends on fuel pump position, on Corvairs the diaphragm stays in the up position against spring pressure, diaphragm is below spring.😉 Same on small block Chevy, diaphragm below spring. This way the diaphragm is spring loaded and ready to flow fuel to the carburetor(s) as soon as the needle opens.

 

Sounds like good advice. But, have any idea how to accomplish this cleanly? Both on a rebuild (put fuel in before assembling top? Seems hard to assemble linkage on the side, and not practical for those kitchen table assembling times of our youth) and after the car sits for a few weeks? Well, electric pump comes to mind, but I thought we were trying not to use those. I can tell you a Rochester H/HV has either a duckbill or two small holes to try to put gas into. You use a chemical wash bottle?

 

All real Corvairs have Carter carburetors, with vents

 

The turbo has a Carter YH.

 

The non-turbo has an aftermarket Carter AFB

 

All joking aside, my mentor stated the fuel bowl SHOULD be filled; not must be filled. On some carburetors, including the H/HV series, this is impractical.

 

Jon

[60FlatTop]

On recommissioning of long term stored cars I connect the brake bleeder bottle of my MyTeeVac to the fuel line at the carb inlet and draw a few bottles through the system. That lets me check and smell the first couple and assure that I am pulling from the tank. Although it does not fill the bowl it brings fuel right to it, wets the fuel pump diaphragm, and gives the starter less cranking. They usually start right up if all the other checks have been done.

 

On this starting issue topic, my point is that there is some compensation designed into the pump for a dead headed needle valve. It may not always work. When the exceptional event occurs don't assume.

An engineer puts great faith in the laws of nature, calculations, weights, and measures. A mechanic trusts nothing.

[Frank DuVal]

1 hour ago, 60FlatTop said:

there is some compensation designed into the pump for a dead headed needle valve. It may not always work.

Right, the spring rate is specified to be under the resistance of the float/needle/seat, i.e. the PSI produced by the pump does not exceed the ability of the needle seat to hold tight. Now the fuel pump makers just throw in whatever spring and think it will work. The spring rate will not change once the pump is built, except maybe to weaken slightly.

 

4 hours ago, carbking said:

The non-turbo has an aftermarket Carter AFB

500 CFM, however, this has running issues when cold in most climates. It's the long runners, not the carburetor. But people still install them then come to the forum to ask why it doesn't work right. I tell them to put the 4 HVs back on. Ha!😁   Compromise was already done by GM. 

 

I do like the Corvairs with the Carter YHs. For those that do not know, they are the stock turbo carburetor. Take a Carter YF and make it a side draft. 

[Machine Gun]

20 hours ago, carbking said:

One other possible issue that has already been touched in this thread. I was taught by my mentor (Carter Carburetor School headmaster) that when installing a carburetor on an engine, THE FUEL BOWL SHOULD BE FILLED PRIOR TO CRANKING THE ENGINE!

 

While that can easily be done before or during installation, it's not as easy after the carb has been installed and the car has been sitting for a couple of weeks. I will poke around the internals sometime next week as I noted in an earlier post and will report back.

[Machine Gun]

11 hours ago, 60FlatTop said:

An engineer puts great faith in the laws of nature, calculations, weights, and measures. A mechanic trusts nothing.

I'm an engineer, and I take offense at your statement. I'm doubly offended because you're right.

Edited June 29, 2022 by Machine Gun (see edit history)

[old-tank]

3 hours ago, Machine Gun said:

On 6/28/2022 at 9:09 AM, carbking said:

One other possible issue that has already been touched in this thread. I was taught by my mentor (Carter Carburetor School headmaster) that when installing a carburetor on an engine, THE FUEL BOWL SHOULD BE FILLED PRIOR TO CRANKING THE ENGINE!

 

While that can easily be done before or during installation, it's not as easy after the carb has been installed and the car has been sitting for a couple of weeks. I will poke around the internals sometime next week as I noted in an earlier post and will report back.

Most carburetors have a bowl vent in the air horn where the bowl can be filled.

[Machine Gun]

36 minutes ago, old-tank said:

Most carburetors have a bowl vent in the air horn where the bowl can be filled.

Yes, mine has one as well. That's where the fuel pukes out. What makes filling the bowl on my carb impractical is that there's a cap over the vent that's riveted in place.

[Bloo]

Down this pipe. A condiment bottle from the dollar store might come in handy.

 

 

 

 

Edited June 29, 2022 by Bloo (see edit history)

[Machine Gun]

24 minutes ago, Bloo said:

Down this pipe. A condiment bottle from the dollar store might come in handy.

 

 

 

 

OK, now I feel stupid. Thanx for the tip.

 

I just had a thought (my first one of the day). If I eventually conclude that filling the bowl prior to running the car when the fuel bowl is empty/dry could alleviate the problem, perhaps an easier way to deal with it would be to crank the car, and then immediately shut it down when it fires and leave it off for a few minutes. Assuming that fuel residue is the issue, the bowl will fill up, and any residue would have a chance to dissolve before I run the car long enough to vomit fuel. Brilliant or bonehead?

[Bloo]

I don't know. I am not discounting the idea that residue gets released less if the bowl is full, but I have never heard of it before. To me, this is a way to get a car to fire up right away when the bowl is known to be empty, for instance when the car has been sitting all winter. I probably never filled one all the way. I would have erred on the side of caution in the interest of not running it over. Not all cars have that pipe but it is convenient when they do. Always secure the air cleaner. It can act as a flame arrestor if the car backfires.

 

Edited June 29, 2022 by Bloo (see edit history)

[old-tank]

1 hour ago, Bloo said:

To me, this is a way to get a car to fire up right away when the bowl is known to be empty, for instance when the car has been sitting all winter.

And you are not activating a dry accelerator pump.  When I fill a dry carb, I use 2-cycle mixture.

[60FlatTop]

2 hours ago, Machine Gun said:

would be to crank the car, and then immediately shut it down when it fires and leave it off for a few minutes.

That's how you wake up a Rolls-Royce/Bentley with an SU carb in the Spring. Standard practice. Just don't fall into a constant depression over it.

[Frank DuVal]

9 hours ago, Bloo said:

Always secure the air cleaner. It can act as a flame arrestor if the car backfires.

YES!

 

And it is difficult to reinstall the air cleaner while the flames are burning the paint off the hood and your eyebrows are missing.

Edited June 30, 2022 by Frank DuVal (see edit history)

[Machine Gun]

On 6/28/2022 at 10:09 AM, carbking said:

Measure:

 

(A) the distance from the air horn gasket to the extreme bottom of the float

(B) the distance from the top of the bowl casting to the floor of the bowl in the area where the lowest point of the float would be

 

Compare - A should be less than B by at least 1/16 inch, preferably 1/8 inch.

 

Also, once you have allowed everything to dry out, and have tested the above, and for the components being sticky, check to see what valve was used by the mechanic that rebuild it for you.

 

One other possible issue that has already been touched in this thread. I was taught by my mentor (Carter Carburetor School headmaster) that when installing a carburetor on an engine, THE FUEL BOWL SHOULD BE FILLED PRIOR TO CRANKING THE ENGINE!

 

I thoroughly inspected the carburetor internals and can find no apparent cause for the overflow when the carb is completely dry. The float and needle move freely and smoothly, and there isn't even a hint of dirt or residue on the needle or in the seat. I have no clue as to what the cause might be. I'm particularly baffled by the fact that I had the overflow issue prior to the rebuild, and there was no recurrence for two years after the rebuild until recently. That seems to exonerate the fuel pump because the pump was not changed since I bought the car. It points to something deteriorating over time. Could the rubber on the needle tip be hardening from use with modern fuels? I can thing of nothing else that would explain the situation.

 

Regarding the above, B - A = 1/8 in. A photo of the needle is attached. It's a rubber-like material.

Edited July 6, 2022 by Machine Gun (see edit history)

[carbking]

Hardening of the neoprene on an accelerator pump is bad.

 

Hardening of the neoprene on a fuel valve will not cause an issue.

 

Jon.

[EmTee]

I have seen those rubber needle tips stick, but usually when the problem occurs there is noticeable wear on the tip where it meets the seat.  You'd see a circumferential indent in the rubber tip where it seals with the seat.  The indentation can cause it to stick shut, or more commonly the wear prevents the needle from completely shutting off the incoming fuel and the bowl will flood.  I can't really tell from your picture what the condition of your needle is, but it looks like it is probably OK...

[Machine Gun]

@EmTee There's no obvious wear on the needle tip, it's like new.

 

I reassembled the carburetor and reinstalled it yesterday. I'll road test it today, but it started up and idled just fine. Since I didn't find anything wrong and didn't change anything, I expect the problem to recur. Things don't fix themselves.

[EmTee]

2 minutes ago, Machine Gun said:

I expect the problem to recur. Things don't fix themselves.

Ha - well, you probably won't be disappointed!

[Rusty Heaps]

I’ve been dealing with a similar problem on my Chevrolet with a 216 with a Rochester one barrel. Start it up and sometimes fuel pukes out of the carburetor. I can tell immediately when it does by the rough idle and wanting to stall out. Pop the hood and gas is pouring over the manifolds, not good! I’ve rebuilt it twice and even installed a new float. I hope you figure out the problem with your car and hopefully it will be the same with mine. I’m about at my wits end.

[Machine Gun]

If you read through the entire thread you'll note that I had the problem from Day One, it disappeared for two years after a professional rebuild, and now it's back with no apparent cause or resolution. I am resigned to live with it.

Edited July 7, 2022 by Machine Gun (see edit history)