Motor flooding when not running

My car ran fine all summer with no issues. Went to start it recently after it had sat for a month or so. It wouldn't start and seemed like maybe it was flooded. Pulled the plugs out and sure enough they were drenched in gas. Cleaned them up and reinstalled. Car started right up. Parked it and about a week later, the same thing happened and again I pulled and cleaned the plugs. Started right up. Repeat once more today. What is likely wrong with the carb to cause of the flooding while the car is just sitting in the garage? Carb is an Edelbrock 750.

I would guess excess fuel pressure pushing thru the needle and seat. this could happen thru heat after the carb sits a few minutes after running, too much fuel pressure, wrong float level or some dirt in the needle and seats. I have had needle and seats gum up and stick open or closed. take the carb apart and look for something and do a hot fuel pressure check.

Needle & seat gummed up & sticking, time for a carb rebuild

Float stuck open.

How do any of the above flood an engine that isn't running?

Kevin

An unvented fuel tank can push gas past the needle/seat when the temperature goes up. Plugged bleeds can lead to a siphon effect in the carburetor but would affect how it runs. Is it rich? The AFB/AVS carbs aren't supposed to do this (leak below float level).

Don't run it until you figure it out. The oil is most likely contaminated with gas.

The guy lives in Detroit, it hasn't been hot enough in 3 months to cause gas in the tank to swell that much !!

Even if the engine flooded from heat soak, it appears to have sat long enough between startups for the gas to have evaporated off the plugs.

So my conclusion is its flooding at startup. Lift the hood, remove the air cleaner and look down the carb while someone's cranks it over. Make sure they are NOT stepping on the gas pedal. If gas is pouring in, check for something sticking the float(s) open. It takes a LOT of pressure to over power floats believe it or not. If you concerned about a backfire blowing your head off, remove the coil wire so the engine doesn't get a spark.

The liquid won't expand much either way, it's the air/vapor in the tank that tries to expand, pushing out whatever is in the way.

Another possibility is the main-well plugs at the bottom of the carb are porous. The plugs are aluminum and may become loose or corrode. Remove the carb. fill with fuel, elevate and watch for seepage out the bottom. Common problem on the older Q-jets. Not so much on the Edelbrock/Carter type.

Whatever, you missed the point ... it hasn't been that hot !!

Easy,,re-do your test with the gas cap off.

THIS; Had an issue w/a billet 850ish carb I built for Shane Studly and his stocker Mopar wagon. Ran great till he topped off the tank then the pressure in the tank literally crushed the ft. brass float(which I no longer use in builds) sticking the needle n seat flooding the car to the point of filling the crankcase w/gallons of gas. Solution, He added a vent to the filler neck and problem solved.....Especially important w/an elec. fuel pump....

Still dealing with this issue. Is it possible for a fuel pump to pump too much fuel when it goes bad? I took the Eddy carb off today and put another one on that I have that came off of a running car a little while back. When I started cranking the motor, once gas got up to the carb it started pouring out all over the place from the top of the carb and also the plugs flooded again.

Sounds like you have gunk in the gas tank sticking the floats opened
I would take the tops off of both carbs and remove the needles to see if the Viton tips have stuff stuck on them or stuck up in the seats in them
Stuff happens hat we don't like but we still have to deal with those problem to correct them, correct

Yes if a mechanical fuel pump air diaphragm hardens you can see an increase in pressure. Doing some of the test recommended would help you isolate. Pressure test, inspect the needle and seat. Something changed from the layover. Since you changed carb it may be fuel system pressure. But a sitting carb even if running previously can have the same issues. So unless you move a carb from a running car directly, you might not be able to cross it off the list.

By the way, even with a non vented gas cap, aren't gas tanks vented twice anyway? Once from rear and one from front via the overflows?

I was just watching some videos on You Tube about checking and adjusting Edelbrock floats. I am going to pull the top off the carb to make sure the floats are not stuck and at the correct position and also that the needles/seats are clean. Is it necessary to replace the gasket between the top and the body of the carb when putting the top back on or can I reuse the existing gasket if it's not broken or brittle?

Does it do it if the car isn't heat soaked? Sometimes the fuel will percolate after you shut it down as it has more time to absorb the heat, it can actually start to dribble out of the boosters, especially if the float is set on the high side.

Yes, it does it when the engine is cold.

I pretty much ALWAYS reuse the gasket. It usually wants to come off with the lid but may be stuck to the body in places. Gotta unstick it from the base where needed before lifting the lid off.

This afternoon I took apart the Eddy 750 carb that was originally on the car when this all started. The floats were not hung up at all and were at the proper settings. I cleaned the needles and seats even though they did not look dirty. In fact, everything inside the carb looked bright and clean. I also blew everything out with air before reassembly. Put the carb back together and back on the car. Pulled all the plugs again and dried them all off. Tried to start the car and no dice. Strong smell of gas and the carb was wet all over. I guess I will have to try replacing the fuel pump although I have never had nor heard of a fuel pump that pumped too much fuel when it went bad. I'm getting tired of all of this. Time to start ridding myself of my cars.

Did you ever check to see what the fuel pressure is? Seems like a couple of tests is better than throwing parts at it.

Did you check the fuel cap.. is this car in a heated shop.. what year is the car

I did open the cap but it made no difference and while I do have heat in the garage, I haven't had it on due to the 40 degree temps. 67 GTX.

If you want to rid yourself of the GTX you can send it my way.

I'm still looking for my old '67, RS23L77152552

I don't know if I missed it but I didn't see if you were using a mechanical or electric pump really doesn't matter but it sure sounds like the fuel pressure is too high and blowing past the seats in the carb.

Critical......I see many people running mechanical pumps w/out a regulator stating that it doesn't matter but it sure the hell does. AND if the car lands on the crown/top of the eccentric, it will hold pressure unlike an electric pumping fuel till it bleeds off....

I don't think that is true as the fully depressed lever compress the spring and creates the vacuum to draw in fuel. No pressure as the cam, lever hold diaphragm up. Plus, non of these mechanical pumps have perfect check valves, in fact usually there is a bleed hole in check valve button for anti-perc purposes. So pressure would bleed back to tank.

I am really confused about the non vented cap also. Unless I am missing something, must be a lot of folks with plugged tank vents and collapsed fuel tanks from the suction/vacuum pulling them inward.

I also think we need a lot more information on where fuel is specifically leaking out from to flood all the cylinders. If the pump overcame seat force and kept needle open the fuel should spill out the vents on the top? Is the top of the carb wet?

If a venture gasket was missing you could wind up with normal fuel level spilling out raw fuel into venture. Or if the bleeds were plugged causing a syphon action that would continue to leak fuel out venturi nozzle. It is even possible an accerator pump nozzle can drip from syphon effect if the closed design.

Having said all that, the fact that two different carbs do this, does lead you to believe something else is at issue unrelated to carb.

If it was a pressure problem with the tank when you removed the line to the carb it would have sprayed gas everywhere. If it's heat soak it won't do it cold and normally will start after cooling off without cleaning the plugs. So I think the car fooled you and us into thinking it flooded when you parked it but I believe the pump pressure is too high and is flooding the car as you're trying to start it.

Mike

"I don't know if I missed it but I didn't see if you were using a mechanical or electric pump"

The fuel pump is a factory type mechanical pump.

"I also think we need a lot more information on where fuel is specifically leaking out from to flood all the cylinders. If the pump overcame seat force and kept needle open the fuel should spill out the vents on the top? Is the top of the carb wet?"

With the original carb, only the plugs were showing signs of excess gas, nothing pouring out of the carb itself.. When I put the 2nd carb on (which was another Edelbrock although lesser cfm), gas was pouring out the vents on top as well as the plugs flooding. I took that carb apart today and it was the same as the first, floats not stuck and set properly and the needles and seat were clean.

"If it was a pressure problem with the tank when you removed the line to the carb it would have sprayed gas everywhere."

Just a little dribble when I disconnected the fuel line from the carb.

"Having said all that, the fact that two different carbs do this, does lead you to believe something else is at issue unrelated to carb."

This is why I asked if a bad fuel pump could over pump fuel vs. the typical loss of fuel pressure.

Keep in mind, I have not changed anything on the car prior to this occurring, just parked it in the garage like normal. The fuel pump and carb. are the same ones that were on the car when I bought it a couple of years ago and I hadn't had any issues of this nature since I bought it.

Change the pump

Well FP can rise when the air dome diaphragm hardens and no longer acts as a damper. Now on compression of diaphragm via spring pressure you windup with a higher pressure since no deflection of the air dome. Whether it is so high to overcome needle pressure not sure but plausible.

EB do require a lower pressure then the orig carters. They use a smaller float and larger orifice which means less force available on the needle to hold back the greater force generated by the FP pressure when a larger orifice is used. Think Brake cylinder diameter. Same effect.

What seems confusing to me, is the bowls probably start out dry or at least low. Your only cranking at a slow rpm and at some point the car should start before the bowl is so high it overflows. So maybe some other issue preventing proper starting that is ultimately leading to a flooded engine too.

so what is your fuel pressure? pretty easy to check

I agree with Dragon Slayer's analysis.

It's very unlikely the pump is causing the problem if the pump was OK in previous uses.
Since its only 40*F and the engine is cold, seems unlikely vapor pressure would be the cause.
It's more likely that the needle and seats are not sealing, or the floats are not floating.


The simplest way to narrow this down is tee a pressure gage into the fuel line. Then you'll know where the problem is.

The simplest way to narrow this down is tee a pressure gage into the fuel line. Then you'll know where the problem is.

This has been stated for days . Guess he does not want to check it.

FYI, it's not that I don't want to check it but rather that I can't at the moment as I don't own a fuel pressure gauge. I wanted to rule out the carb being the problem first before buying a gauge to check the fuel pump pressure.

True

You can buy combo gauge at HF for $13.00 How many days have you wasted?

The only time I have wasted is reading your posts in this thread. If all you have to contribute is smart-azz remarks why do you bother to post at all?

In 1992 my 67 GTX broke down on the side of the highway and it took me 1 1/2 hours later to get back to get it and it was gone. I had owned it since I was 16 years old and had it 14 years . I have not heard anything about it since.

Well, I'm here to tell ya it IS true and that I have seen the regulator hold pressure when shut off so it is valid sometimes weather normal or not....

6 Pax there are only 2 things that can make the gas overflow out of the carb. Too much pressure or the needle and seat being open. Also when putting the carb back together make sure the metering rods are in the main jets. The only reason I mention this is I bought a car from a friend that would load up stopped in traffic but would otherwise run fine. He had the carb an AFB rebuilt at a well know shop that had a good reputation but when I took it apart one of the metering rods was bent in a L and not in the jet. Anythings possible.

Wish I lived closer so I could stop by and help you find the problem.

Mike

Since the first reply 15 days ago people have been saying fuel pressure, yet you ignore it. Why ask for advice if you won't take it? Yet when someone points out the obvious you get all hot and bothered and start name calling.

It's hard to be sure whats going on sometimes when just reading response's.

There's always the chance it could be getting flooded by you pumping on the gas trying to start it and possibly in combination the ignition might not be working. If it has an MSD it won't fire with a low battery but will crank over fine. You can always fill the carb put fresh plugs in it and pinch the fuel line shut and see if it will start. If it doesn't it ain't the pump.

Let us know what you find.