Carb flooding periodically

[Brtele]

1965 401 carter afb floods periodically on startup if I haven’t started the car in 5-6 days.  If I shut the engine down quickly and tap the carb’s float area, I can get the car started back up and it’ll run normal.

 

 I’m thinking the fuel is evaporating or leaking down and the float drops to the lowest setting and gets stuck, letting fuel to continuously pump in.

 

 Short of taking the carb off and going through a rebuild - any advice?

 

 Thanks,

 Brandon

[telriv]

Remove the top & check "Float" drop.

 

Tom T.

[60FlatTop]

You could check your heat riser. The AFB vents the hot vapors to the throttle plate area and out to the atmosphere through two vent holes in the body. This helps keep a hot engine from flooding. If your heat riser is malfunctioning there could be enough heat to evaporate all the fuel in the bowl as the engine cools. One problem exacerbates the stick float, cause the flooding, and diverts your attention. Worth checking. There are a lot of heat risers that don't work right.

 

And, if it doesn't have a dry float bowl you would never notice to sticky float.

[Brtele]

4 hours ago, 60FlatTop said:

You could check your heat riser. The AFB vents the hot vapors to the throttle plate area and out to the atmosphere through two vent holes in the body. This helps keep a hot engine from flooding. If your heat riser is malfunctioning there could be enough heat to evaporate all the fuel in the bowl as the engine cools. One problem exacerbates the stick float, cause the flooding, and diverts your attention. Worth checking. There are a lot of heat risers that don't work right.

 

And, if it doesn't have a dry float bowl you would never notice to sticky float.

I recently removed the exhaust heat riser valve from the passenger side exhaust manifold. The valve and thermostat spring had locked up so I completely removed the valve.  Would I still need to worry about this as a source for the carb to be dry?

[EmTee]

9 hours ago, Brtele said:

Would I still need to worry about this as a source for the carb to be dry?

No, not if you have removed/disabled the heat riser valve.  My experience is the normal heat from the engine is enough to cause the fuel to boil-off after shutdown.  The problem will be exacerbated if you're still burning-off the more volatile winter blend gasoline.

[60FlatTop]

I took my '60 Electra out for coffee this morning. It is a 401 with a working heat riser that starts cold with one pump and has no hot start issues. I got home with it fully warmed up at 180 degrees and used an infrared thermometer to check the carburetor base and the adjacent manifold and heat crossover temperatures. This car does have a 4GC but temperatures would be similar.

 

Running at idle the temperatures were all about 145 degrees. I shut the engine off and checked about 8 to 10 minutes later. The carb and manifold had risen to about 155 and stable.

The right hand exhaust manifold was at about 390 degrees. They looked reasonable to me. Knowing my car has no issues that would be a good base to check your car against.

 

The Carter AFB has something like five clean out plugs that could leak after years. That would show up as fuel stains on the manifold if they leaked.

 

Elmtree and I are on the same page. The empty fuel bowl is the problem.

 

Then there could be the unlikely problem you are parking next to a car with SU carbs. They leak and the floats stick and it might be contagious. I have a friend who runs a Rolls-Royce shop. During the Spring recommissioning time he has received frantic calls about fuel spilling all over on the first start up. He will ask "How long ago was that?" The owner answers "About 15 minutes." He will say " It's OK now. Go ahead and start it." To their amazement the car starts and runs admirably until the next Spring. Some SU's even have an overflow pipe so you can get home. Don't park next to one.

[EmTee]

Just FYI, I had removed the air cleaner from my '38 while I was making tune-up adjustments.  After making a test-run with the car I returned home and immediately pulled it into the garage and shut it off.  As I was making a post-ride visual inspection of the engine I heard a faint 'crackling' noise as my head passed by the carburetor.  I stopped, thought a moment, then put my ear over the air horn and I clearly heard the sound which was similar to that of water boiling in a pot on the stove!  I have my heat riser wired open until I can confirm that it's working properly, so extra heat from that wasn't a factor.  I was running 'winter-blend' gas at that time, so maybe it will get better when the summer gas is available, though I expect it'll still be much more volitile than what was available in the 1940s.  Since the car has an electric fuel pump in series with the mechanical one I just run the pump for 10~15 seconds to refill the bowl before starting the car for the first time after sitting overnight.  It then starts right up and no priming is necessary for subsequent starts the same day.

 

BTW, my '67 Riviera and '64 GP act the same when starting cold after sitting for an extended period (at least overnight).  Those cars don't have electric pumps, so it takes 20~30 seconds of cranking to get enough fuel for them to 'wake-up'...

[Brtele]

3 hours ago, EmTee said:

Just FYI, I had removed the air cleaner from my '38 while I was making tune-up adjustments.  After making a test-run with the car I returned home and immediately pulled it into the garage and shut it off.  As I was making a post-ride visual inspection of the engine I heard a faint 'crackling' noise as my head passed by the carburetor.  I stopped, thought a moment, then put my ear over the air horn and I clearly heard the sound which was similar to that of water boiling in a pot on the stove!  I have my heat riser wired open until I can confirm that it's working properly, so extra heat from that wasn't a factor.  I was running 'winter-blend' gas at that time, so maybe it will get better when the summer gas is available, though I expect it'll still be much more volitile than what was available in the 1940s.  Since the car has an electric fuel pump in series with the mechanical one I just run the pump for 10~15 seconds to refill the bowl before starting the car for the first time after sitting overnight.  It then starts right up and no priming is necessary for subsequent starts the same day.

 

BTW, my '67 Riviera and '64 GP act the same when starting cold after sitting for an extended period (at least overnight).  Those cars don't have electric pumps, so it takes 20~30 seconds of cranking to get enough fuel for them to 'wake-up'...

I drove the Riviera to work this morning and had recently ran the car on Sunday.  Upon crank, the carb acted like it had a little gas (sputtered a couple times), but cranked for a good 8-10 seconds while the fuel made its way to the carb.  It did not flood this morning.

 

Based on the above, I'm thinking the fuel is either evaporating (very quickly - 2 days) or boiling upon shutdown.

 

When I get home from work, I'll take some infrared temp readings around the carb base prior to shutdown and 2-3 minutes after shutdown.

[Brtele]

No way is the carb getting so hot all the fuel is boiling out. When I Went to lunch and left work today, it started quicker than I could get off the key.

 

Carb temps after a spirited drive home in upper 80 degree temps - 150-160 everywhere. Intake wasn’t higher than 215 anywhere.

 

This leads me to believe it’s either evaporating really quickly or leaking out of the carb and into the manifold.

 

 Positive note: all exhaust ports are hot while running and within 10% temps of each other - they’re all firing 

 

Non-positive note: I have a slight tick on the drivers side valve train.

 

 Secondary positive note: way fun driving it to work and back - 45 minutes round trip. But was consistently looking for a crash landing spot at each red light in case the brakes failed, lol.

Edited May 11, 2022 by Brtele (see edit history)

[60FlatTop]

Sucking around 15,000 cubic feet of air on a 45 minute drive will keep that intake manifold surprisingly cool.

 

[Brtele]

It should also be noted, the last time I filled the tank I had to use 93octane, but it contained 10% ethanol.  Yesterday I filled up the tank with 91 No Ethanol.  It'll be interesting to see if the no-ethanol fuel starts holding longer before evaporation.

[carbking]

15 hours ago, Brtele said:

No way is the carb getting so hot all the fuel is boiling out. When I Went to lunch and left work today, it started quicker than I could get off the key.

 

Carb temps after a spirited drive home in upper 80 degree temps - 150-160 everywhere. Intake wasn’t higher than 215 anywhere.

 

This leads me to believe it’s either evaporating really quickly or leaking out of the carb and into the manifold.

 

 Positive note: all exhaust ports are hot while running and within 10% temps of each other - they’re all firing 

 

Non-positive note: I have a slight tick on the drivers side valve train.

 

 Secondary positive note: way fun driving it to work and back - 45 minutes round trip. But was consistently looking for a crash landing spot at each red light in case the brakes failed, lol.

Gasoline will evaporate at 140 degrees F.

 

Typically, gasoline will start boiling out of the carburetor INTO THE AIR CLEANER AND INTAKE MANIFOLD immediately after shutdown. Because it takes some time for the vapors in the air cleaner and intake to disperse through the air cleaner air intake into the surrounding air; cold starts the same day are generally not an issue. After some time elapses (maybe 1~3 days) all of the vapors will have dispersed, the carburetor bowl(s) are dry, and a cold start requires gasoline to be pumped to the carburetor.

 

Some carbs are more prone to evaporation than others. And different engines hold more heat than others. The dual genuine Carter AFB's on my performance Ford shop truck will have COMPLETELY DRY BOWLS 30 MINUTES AFTER SHUTDOWN! The genuine AFB's are probably among the top five for evaporation, but not as bad as the imitation AFB's.

 

Jon

 

[carbking]

6 minutes ago, Brtele said:

It should also be noted, the last time I filled the tank I had to use 93octane, but it contained 10% ethanol.  Yesterday I filled up the tank with 91 No Ethanol.  It'll be interesting to see if the no-ethanol fuel starts holding longer before evaporation.

Alcohol gets blamed for many things (and it should!  ), but quick evaporation of the gasoline is not one of them.

 

Gasoline evaporates at 140 degrees F.

Alcohol evaporates at 172 degrees F.

 

Jon

[Brtele]

1 hour ago, carbking said:

Gasoline will evaporate at 140 degrees F.

 

Typically, gasoline will start boiling out of the carburetor INTO THE AIR CLEANER AND INTAKE MANIFOLD immediately after shutdown. Because it takes some time for the vapors in the air cleaner and intake to disperse through the air cleaner air intake into the surrounding air; cold starts the same day are generally not an issue. After some time elapses (maybe 1~3 days) all of the vapors will have dispersed, the carburetor bowl(s) are dry, and a cold start requires gasoline to be pumped to the carburetor.

 

Some carbs are more prone to evaporation than others. And different engines hold more heat than others. The dual genuine Carter AFB's on my performance Ford shop truck will have COMPLETELY DRY BOWLS 30 MINUTES AFTER SHUTDOWN! The genuine AFB's are probably among the top five for evaporation, but not as bad as the imitation AFB's.

 

Jon

 

Dang it Jon - thanks for the explanation - makes a lot of sense. 

 

Was this an issue from Day 1 for cars that left the showroom with a Carter AFB?

 

I wonder why my float is sticking at the bottom after the fuel evaporates out.  As Telriv suggested, I need to take the top off and inspect.  With all this free time I constantly have, I don't know why I haven't done it yet.  Dang.

[carbking]

The AFB came out in 1957. Gasoline in 1957 had less garbage (thanks, EPA) than it does today, and did not evaporate so readily. Still one of my all-time favorite carburetors.

 

The float(s) should NEVER stick at the bottom!

 

Each modern carburetor has TWO float settings: (1) with valve completely closed, (2) with valve completely open (a.k.a. as "float drop").

 

Both should be adjusted when rebuilding a carburetor.

 

Although I am too old to state it doesn't exist; I have been rebuilding carbs since 1959, and have yet to see a modern car where the float drop adjustment would allow the float to hit the bottom of the bowl.  I generally measure the top of the bowl to the floor of the bowl, subtract 1/16 inch, and adjust accordingly.

 

While not applicable to your carburetor, some much older carburetors have a much more finite adjustment on closed valve adjustment. This is the FUEL level, not the float level, in the bowl at a specified inlet pressure.

 

An example: 1936 Buick FUEL LEVEL should be 5/8 inch below the top surface of the bowl with an inlet pressure of 3 psi.

 

While more modern carburetors, due to valve to fulcrum placement, are less susceptible to pressure changes; they are still susceptible. This is why many folks have issues with adding an electric pump, or just as bad, buying a new "name brand" mechanical pump from a FLAPS that was made in a country with a name of 5 letters, and starting with the letter C (hint - it isn't Chile).

 

But I digressed.

 

If your float drop is correctly adjusted, the float will not stick on the bottom of the bowl; BUT STILL MAY STICK AT THE HINGE POINT! Some of the fuel we currently get appears to simply be thinned glue! When it dries out, it becomes glue!

 

Jon

[rocketraider]

18 hours ago, 60FlatTop said:

 

There is nothing more American than an arrogantly big damn American car tearing down a dirt road kicking up dust in its wake!👍

 

Side benefit: running all the crap gas out of it so it doesn't do hateful things like have been described in this thread!

[60FlatTop]

There is nothing more rural American than having your son lying on the side of a dirt road with his camera while his father comes barreling his way at 60 MPH on biased tires and single piston brakes in a cloud of dust.

 

That's after chasing away a few turkey vultures that were feasting on a deer carcass at the corner. The vultures looked on from the hedgerow with interest.