Solution to Severe engine flooding

Here's my take from encountering this problem years ago. Odds are the car will not start because:

1) The gasoline has washed the oil off the cylinder walls, and you aren't getting enough compression. In this case you'd need to squirt some oil into the cylinders on top of the pistons and spin the engine so the oil gets onto the cylinder walls and seals the rings. 

2) Or the gasoline itself is old and has degraded/separated into its component parts. I've had this problem with small equipment that sat up too long. Requires draining all the old gas out and replacing with new.

3) Or you still have the flooding problem, and the mixture is too rich to burn. If so, find and fix the problem causing the flooding, and take the spark plugs out and let the engine set for a while so the excess gas can evaporate out of the combustion chamber. You may still need to oil the cylinder walls.

4) Or you have a ruptured fuel pump diaphragm that is pouring gas into the engine pan. I've seen instances of the entire crankcase filled with gasoline on old Chrysler slant 6's. They would not start despite getting fuel and spark. But sometimes they'd blow the entire pan off. Again, the problem was the gasoline diluted the oil and there was no compression.

5) Or this is an older car with a vacuum tank with a stuck float, due to a loose bushing above the float. Gasoline then gets sucked directly into the intake manifold via the connection between the manifold and the vacuum tank, completely bypassing the carburetor.

6) Or your carburetor is gummed up and the float is stuck down, or is full of gas and has sunk. This may be the most likely cause, rather than a carburetor mis-adjustment.

You didn't mention the car or the type of fuel system it has. More information would help.

jrbartlettNov 3, 2017

You didn't mention the car or the type of fuel system it has. More information would help.

What a party - pooper - not giving us a clue as to what in blue thunder the vehicle is.....is part of the fun  !

jrbartlett , I'd say you completely nailed almost all possible causes and also solutions. Appreciate your precise and efficient reply!

The problem is occurring in a 1947 Desoto s11. 

Damn, I hadn't thought about the lack of compression due to the gasoline. I know the gasoline had mixed with the oil, as was evident when I changed the engine oil.I don't think there is dirt or gum inside the carburetor, as it is new, and the gas is also new and the gas tank had been washed. The carburetor gasket is good, and the carb isn't itself flooded, only the intake manifold.

I think it narrows the problem down to the carburetor adjustment and/or fuel pump pressure. The fuel pump is a mechanical type that attaches directly to the crankshaft of the engine.

I know that the fuel pump must be sending much more gasoline than what is used by the car, as cranking it for 20 seconds or so is already enough to fill up a 1litre bottle.I don't know if this is normal or not. I am confused though as what keeps excessive gasoline from entering the intake manifold.Is it the idle mixture screw, is it the float needle/valve?What happens when the bowl is full and the fuel pump keeps pumping?

The fuel bowl and float valve work exactly like the float and valve in a toilet tank. Level comes up to normal, valve shuts off. Does that help?

It is normal (and also desirable) for the fuel pump to be able to deliver a whole bunch of fuel when just pumping into an open hose.

Mechanical fuel pumps usually deliver about 5psi or 2.5psi depending on what era they are from. The shop manual should have the answer.

Yeah, but when the bowl is full, and the fuel pump keeps pumping, wouldn't that damage it?....I guess not because there is not enough pressure, correct?

My other question is, can the main jet be adjusted?Or does it depend on the carburetor( some are adjustable others aren't)

yeah , my manual says 3.5psi to 5.5 psi.

tom61Nov 5, 2017

Yeah, but when the bowl is full, and the fuel pump keeps pumping, wouldn't that damage it?....I guess not because there is not enough pressure, correct?

No. The pressure is set by the spring inside the pump. If no gas is used, the diaphragm just stays up, and the arm doesn't pump the diaphragm anymore until some gas is used and the diaphragm comes back down.

tom61Nov 5, 2017

My other question is, can the main jet be adjusted?Or does it depend on the carburetor( some are adjustable others aren't)

On almost every carburetor the mains cannot be adjusted without changing parts. The mains are adjusted by changing the jets and/or metering rods.

Exceptions exist, like some industrial carburetors, and a very, very few "universal replacement" carbs from long ago. Also, there were mixture adjustments on some very old cars (brass era).

The short answer is you will never see it.

Let me rephrase my earlier question, If the fuel bowl is not adjusted properly, so that there is too much fuel, where will the excess fuel leave?

Thanks guys, that sure answers alot of questions!

tom61Nov 5, 2017

Let me rephrase my earlier question, If the fuel bowl is not adjusted properly, so that there is too much fuel, where will the excess fuel leave?

Anywhere it can get out. The main jet, the bowl vent, etc... Mostly it will run over into the intake manifold. It may also run over on the outside.

Bloo, I'm pretty sure the gasoline is running over into the intake manifold, because after I crank it for a little bit ,the intake manifold floods with gasoline.But no gasoline leaks on the outside

I'm gonna open up the carb, and check the float adjustment....as I bought the carburetor new, I had initially assumed it already came adjusted, but I know this is now not the case.

When you mention

BlooNov 5, 2017

 Mostly it will run over into the intake manifold.

Where exactly would this be? would it soak through the gasket and then enter through to the main jet which then discharges too much gasoline?

Damn, I probably sound like a 3 year old that says 'why' all the time....

I'll let you all know how it goes.Thank for the help received so far!!

It wouldn't have come misadjusted. If it is misadjusted, whoever built it screwed up. If this is that modern-ish carb from your other thread it might have a plastic float. If it does, you will need to weigh it (on a grams scale). They fail by absorbing gasoline and getting too heavy to work properly. If it is a brass float make sure there isnt gas inside.

The gas doesnt need to soak through anything to come out. The float valve just keeps the bowl to a constant level, literally like a toilet tank. The jets are open to the bowl. Gas is sucked out of the bowl by venturi vacuum. The airflow through the venturi (or past the throttle plate while idling) pulls the gas out of the bowl.

The gas in the bowl is always sitting there ready to go. It should not be running over.

Common causes of running over:

1) Float is sunk, or too heavy, or misadjusted

2) Float valve doesn't seal (look at the tip, if it is rubber, is it split? If metal, does it have a groove worn?)

3) Fuel pressure too high. This is extremely unlikely on your Desoto since you have a stock mechanical pump. Are you sure there isn't an electric pump running in the back somewhere?

Good luck!

I opened up the carb today, and I found an extra screw and nut stuck between somewhere , and a needle valve inside the carb.

I know it didn't come adjusted because when it came the idle mixture screw was opened all the way.

If they didn't adjust it properly when they should have, I wonder what else could they have done.

I bought it brand new from a US company called 'southwest performance parts'

The pump is the stock mechanical pump.The valve is the rubber tipped one.Everything seems to be good.

I even blew into the gas inlet and no air went in

They don't adjust the mixture screw for you. That has to be done on the car more or less like I posted earlier.

They do adjust the float, or at least they should. Nobody who buys a rebuilt carb is expected to do that because it requires taking the carb apart, measuring carefully, and bending stuff.

Bloo, thanks again for the reply and your experience and insight.

I found it strange that they had an extra needle lying there inside the gas bowl and an extra bolt & nut outside.

Anyway, I was having difficulty getting it started again, even after changing oil and installing new spark plugs. I even used 'liquid fire' to try to get it started wit no luck.

I've concluded that due to the cold weather, any starter fluid that I sprayed in there condensed to rapidly to be able to be ignited by the engine.

Also, It seems that the fuel float is still too high (even though I bent it down a tad) as there is still too much gas coming through.

Also, when I turn the mixture screw all the way down, nothing happens, much less the car stalling.

From what I understand, the car should stall when the mixture screw is turned all the way closed, correct??Also, the spark plugs quickly develop a thin layer of carbon which further suggests to me that the mixture still has too much gasoline. Fortunately thought, the intake manifold no longer floods!!

So I am thinking that what I still have to do is lower the float a little more...Or could it be a jet that is too wide?I've heard of jets that are too rich...the manual even suggests to change to a 'leaner metering jet when in locations of high altitude'.

So instead of lowering the fuel float I should change the metering jet? How can I tell the difference?

Also, Bloo, you mentioned how it is only the vacuum from the engine that sucks the gas in, and the height of the fuel inside the bowl is what dictates how much fuel actually goes to the engine. Can these holes be seen? Or are they internall?

I've attached a file that shows some of the symptomes I had, problems I encountered, tests I did and some solutions I've found, if it is of any help to any one out there with a similar problem.

Once again bloo, thank you so much for all the help you've given. I'll further tackle the problem tomorrow and let you know of any updates.

flooding problem problems, symptomes & solution .docx

tom61Nov 9, 2017

Also, It seems that the fuel float is still too high (even though I bent it down a tad) as there is still too much gas coming through.

You have gotta set that by the book for whatever car the carb came off of. TIny changes in height do affect the mixture, but there isnt enough range of "ok" to use float height as an adjustment. If it is too low you will run out of gas going around corners. If it is too high, it runs over. Is that a plastic float? If so it might be shot.

I don't know what the internals of this carb look like exactly, but that valve needs to shut OFF. No gas can leak around it. Theres probably a gasket washer on the threaded part that screws into the body. Is it sealing?  On carbs where the float, valve, and hinge are all on the same casting i used to blow through the fuel inlet. When I would turn it upside down so that it was closed with the weight of the float on it, it needed to shut OFF HARD. The height needs to be set to whatever the book says. I cant stress this enough. There is also probably a spec for "float drop" , or how low the float can hang. This keeps the float from hitting on the bowl when it goes all the way down.

tom61Nov 9, 2017

Also, Bloo, you mentioned how it is only the vacuum from the engine that sucks the gas in, and the height of the fuel inside the bowl is what dictates how much fuel actually goes to the engine. Can these holes be seen? Or are they internall?

The height makes slight changes in mixture, but mainly determines whether it runs over or not. The jets are used for determining the mixture.

tom61Nov 9, 2017

From what I understand, the car should stall when the mixture screw is turned all the way closed, correct?

Yes. It should stall. This is a 99.9 percent sure sign the float bowl is still running over. If the engine keeps running, the engine is getting gas from something besides the idle jet while idling. Some carbs have a diaphragm-type power valve that can pop. Nearly always though, it is just gas running out the main jet because the float level is too high or the float valve is not shutting off.

I don't think this carb has a diafragm, and I can't imagine a busted float on a new carb. Also, it seems pretty light compared to the float on the old one.

I'm gonna lower the float down another tad and see how it goes.

Would you know of a place/website where I can get specs for this carb? I'm specially interested in the size of the metering jets.

-Nothing like working on a vintage car while listening to vintage music

As I said, the acceleration response is much much better than it was before. Certainly the new engine oil has made a large difference for the better.

My only concern is still that the engine won't stall with the idle screw all the way down. In fact, it won't even make a difference whatsoever.

The only cause of this can be a float that is too high, or am I missing something?

Most likely it is too high.