How do I prevent post shutdown flooding?

I have an issue with my Holley 1904 carb on my '54 Ford.

The car starts fine when cold and runs fine while driving. However, it always floods out when I shut it off warm and park at the store or whatever. The other day I had the aircleaner off, doing something, and noticed that when I turn the car off, the fuel level starts to rise in the float bowl. It's almost as if the heat in the fuel line due to proximity of the engine block creates a thermometer rising effect and fills the bowl completely full, at which point gas runs down the intake for minutes upon minutes.

The float is adjusted properly. I don't have a new needle to throw down there, and have no idea of the condition of the seat, but it should be 'clean' as it's going to get.

What can I do to stop this from happening? When the car is running, the needle/seat is apparently a good enough seal to fight back the fuel pump, but when I shut it off, up comes the fuel...

Here's a photo demonstrating it flooding itself out (note for normal level): http://www.flickr.com/photos/luketrash/181225030/

 

Do you have an electric fuel pump? That could do it if you leave it on. I don't think that it's the heat think because I don't think that would be enough to overcome the needle and seat. Maybe you need to check the needle and seats and float level adjustment. Good luck.

 

It's the stock, mechanical pump.

I just read elsewhere that a sticky heat riser valve on the exhaust/intake link can get stuck and too much heat there can cause the same effect.

Does anyone have advice on both cooling down the fuel line with insulation, or figuring out if the heat riser system is working properly?

 

You could try lowering the float a slightly.

 

The issue is that even with the float completely submerged in fuel, it doesn't provide enough 'oomph' to the needle to cut off the fuel flow.

I need to measure the movement of my heat riser valve between a cold and hot engine to see if the spring is even doing anything. It rotates freely, but the spring might be inoperable.

 

It's funny you post this - I have a buddy that is having the same problem with his rochesters carbs on a 2x3 set up & mechanical fuel pump, flooding after shut down. He changed all the float levels, needle and seats - still leaking after he turns her off.
Does anyone know the cause and the fix?

 

It's either got too much fuel pressure coming from that alledged "stock" fuel pump or the gas is getting past dirt or what have you lodged between the needle and seat.
The first thing you need to do, if that pink shit on the fuel inlet pipe fitting threads is anything even reomtle like teflon get rid of it first.
That isn't a pipe thread anyway so it's not doing ay good and may be letting shreds get into the fuel supply.
It could also have a heavy float that doesn't give enough boyancy/resistance to over power the fuel pressure and keep the valve shut.

It'll also do that if the fuel tank level is higher than the carb float bowl level, and there's any dirt at all. That's why motorcyclse have petcocks that you have to shut off every time you park.

 

Back to the basics - there is only one way for more fuel to get in a carbuertor and that is through the needle and seat. I think you've got to recheck or replace it. It doesn't take much for them to leak

Why it doesn't happen when the engine is running is a bit of a mystery; mabey on shut-down heat does warm the gasoline and boil it, thus building up pressure

Just my $.02

 

Interesting...my old Jeep has the same problem but it also happens when it's running. It just slowly floods itself out.

Hank

 

on all my cars i run a phonlic spacer(heat shield) between the carb and the intake.it keeps the heat from boiling the feul in the float bowls,and flooding the motor.i saw these at jegs.


Manufactured from advanced phenolic thermoset plastic and engineered to withstand extreme high intake manifold temperatures, these spacers were designed to insulate and reduce heat flow to the carburetor keeping it cooler to allow a denser fuel mixture to enter the engine and produce more horsepower. Available to fit the standard Holley/Carter and Quadrajet four-barrel bolt pattern in your choice of either an open center or four-hole straight bore design, these spacers measure 1'' thick and are packaged complete with gaskets, studs, nuts, and washers. A must for any serious racing enthusiast

 

Check the float itself. If its got fuel in it replace it with a new brass float.

 

good question, too bad i don't have a good answer!

i'm running 3 holley 1904s on my falcon, and have the same problem. it's simply not most of the obvious "idiot" problems listed above. i've dicked with the float level, tried many different floats and needles and seats, both new replacements, old stockers and NOS ones(they don't make them to original spec anymore). i've adjusted the fuel pressure down to the point that it goes lean by the time you hit third gear due to such low fuel pressure. nothings taken care of the problem. about the only practical thing i haven't tried is a phenolic spacer, which would have to be made from scratch since no aftermarket company is willing to step up and supply the MASSIVE demand for these shitty 1bbl carbs! mine are glass bowls, and sure as shit after shutting it down you can watch the fuel fill the bowl through the needle and seat and percolate.

maybe i'll try a bypass type regulator one of these days to keep the fuel supply cooler, but that's a bit of work to accomplish.

i suppose one could try to custom build floats out of the plastic material that most newer carbs run, it may be more buoyant than the brass floats, but i dunno if it would help.

i've just learned to live with it so far. hell, i wish i could find a huge secret stash of these carbs, i'd like to do a 6x1 setup with em, i think they look a helluva lot cooler than 97s, for no reason other than the glass bowls.

 

I am hanging on to every word of this thread. I've been fighting this same issue on the Autolite 4100 in my 66 Galaxie for a while now. I have been through the carb 4 times even after I rebuilt it. Clean as a whistle. Blown out every passage with 150 psi. NEW floats, adjusted floats, added a fuel pressure regulator and turned it down to 4 psi.

The only factors that changed...

Went from stock 4 barrel cast-iron intake to Edelbrock.
Replaced the stock filter with one of those glass fuel filters.

I'm thinking I am getting more heat soak from the aluminum intake than the cast iron

or...
the after market filter doesn't filter particles fine enough and I should go back to the stock filter.

 

Well, as mentioned above, my carb works fine when the car is running. The fuel level rises 2/3 full and stops. The float/needle are able to overcome the 3psi or whatever the fuel pump delivers.

However, when the car is shut off, I can stand there and watch the fuel level rise up in the glass bowl (rather quickly, I might add) Since the fuel pump is mechanical, and not moving, and the gas tank is at least 1.5 feet lower than the carb, it's pretty scientific to watch. It's heat related, and I can't figure out if it's the fuel line sitting next to the block, or the heat riser on the exhaust/intake setup. Probably a little of both. The phenolic spacer looks like a great idea, but I'm not sure where I'd purchase one for the 1bbl carb. Yep, that's pink pipe tape on my threads. It leaks otherwise, and I don't have a local source for a new brass fitting. I don't have the tape in the fuel line though. It's back around the threads.

It's quite possible my needle is getting a weak seal, but it manages to work just fine when the fuel pump is working against it. This heat related fuel flow, however generates more pressure/suction. I think I saw this on Mr Wizard when I was a kid.

 

I second this! I had the same problem, but on a ford 302 with both a Holly motorcrap carb, and an Edelbrock AFB 4bbl carb. Figured out the problem was heat saturation in the carb, was causing the fuel to percolate out the vents. I put about 4 thin metal and paper spacers under it, and it fixed it. I would have liked to use the plastic, but didn't have the underhood room. I bet it would work even better. I want to get a plastic aircleaner, because my metal one holds a lot of heat on the motor.

 

i hadn't thought about that Mojo. I'm using the oil bath air cleaner, which is all steel, and large. I imagine it's a great heat retainer. I think I'm going to cut myself some asbestos gaskets tonight and stack them.

 

Doesn't Edelbrock, or somebody, make a manifold that has a space between the carb mount and the cradle at the bottom that's supposed to solve this problem without the carb spacer? Seems it might help with the heat saturation problem. If that's not the heat source then trace the fuel line back to the tank. Obviously, if the fuel line is anywhere near the exhaust or block, that's another problem and it needs to be moved. If you have a laser thermometer, test the temp of the line. I wander if the carb has a vent or something that is blocked too. This almost sounds like a syphon, if I read it correctly, that the fuel bowls were filling up after the engine was turned off. Anybody else, I'm all out of idiot ideas on this one.

 

Ok if you follow these steps you will cure the problem I have has the same thing many times here in the south.

I have a 84 GMC truck with a LT-1 350 in it and I installed a Edelbrock EPS performer intake with a 600 cfm AFB carb as soon as I did when I shut the engine down it would start to boil the fuel and starve for fuel under heavy loads. (I also installed a Holley Mech fuel pump 110 GPH at 6 psi.

1. Make sure you have 5 to 6 psi of fuel pressure thats more than enough for a stock engine.

2. Move all fuel lines AWAY from teh engine most GMs will route it behind the alt, waterpump ect all this does is blow heat on the fuel line and allow it to soak up heat when sitting.

3. Use the Phenolic spacer between the carb and the intake manifold it will be one of the best purchases you will make it helps make a bit more power and cools the body of the carb a lot!

4. DONT USE that clear glass fuel filter there are a lot of reasons for this and make sure the fuel filter is mounted away from heat sources in fact install it at the fuel pump down low where there is not so much heat from the engine to affect it.

Or even better spend a little more money get the big racing filter and mount it on the wheel well of something the thing to remember is keep it away from heat as much as possible.

5. Make sure you mixture is right for the setup if its to lean it may run hot just a suggestion.

6. Go to a junk yard or whatever get creative and try to figure out a way to vent fresh outside air right into the carb instead of the air in the engine compartment you will be amazed at the power increase more so in a hot climate.

I did all of these things and my fuel problems vanished even when its 250 degrees under the hood!

By the way by switching to the Edelbrock performer intake and their AFB (Which is really a Carter) I picked up 2 more miles per gallon on the HWY and more low end torque.

Jim Mackinlay

 

There is an old trick to getting flare fittings to seal without tape/sealer.
Disconnect the fitting. Slide the nut back on the line to expose the flare. Wrap the tubing behind the flare with kite string. (about 2 wraps) Be sure no string gets to the sealing surface of the flare, only the side the nut tightens against. Reinstall the line and tighten to spec. Voila, no leaks...and it's hidden by the flare nut so nobody even knows you had an issue.

 

Harley Davidson already makes your answer.

Last 10 or so years of production use a vacuum assisted petcock. No vacuum, and it doesn't matter what position the switch is in, it ain't flowing fuel. Dunno how hard it'd be to hide or modify em, but the mechanism is out there.......

 

Please keep in mind that with a mechanical fuel pump you can have some residual pressure even with the engine not running, so a marginal needle/seat/float combination can lead to this. Think about how the mechanical pump works. The cam lifts the plunger and draws fuel into the pump, and then when the cam turns so that the plunger is free to move, the spring in the fuel pump "pushes" the fuel into the carb. It's not the action of the cam against the plunger that moves the fuel from pump to carb. So if you shut the engine off and it happens to stop with the plunger not in contact with the cam, which in most cases is going to be more than half of the cam's rotation, that ol' spring is going to keep fuel pressure on the needle and seat until "leaking" allows the plunger on the pump to contact the cam surface. Now add some heat soak to the mix, and the pressure actually goes UP higher than it does during normal operation. A GOOD pressure regulator between the fuel pump and carb should prevent this from happening, but usually they look out of place on the stuff we build............

 

Here's what I do, or used to do, when I used to have that problem.

Just to get you by for today until you fix it more permanently...

The quickest and easiest way I found to deal with it for now is what I used to do-

I used to simply flip a switch to shut off the electric fuel pump about 20 -30 seconds before I shut off the engine so the carb was close to dry before I shut down the engine.
I used to have the habit of flipping off the pump switch as I entered a parking lot, and by the time I pulled into a parking space, the carb was close to empty. It always started easily when I did that.

I later learned that I could turn it off about 2-1/2 blocks before home, stop at two stop signs and just make the driveway before it stumbled. I know some will say it isn't fun for long, but I made a game out of it for a while until I fixed it more permanently later. My kids used to like the "game" to see how far we could go on one carbful of gas with the pump turned off

An empty carb doesn't boil, if the fuel in the hot fuel line boils, there is room in the carb so it won't spill over into the manifold, and when you turn on the pump 4-5 seconds before hitting the starter you will have fresh, cool fuel to start the car with.
Makes a world of difference.

*********************

Long term fix....

Keep the carb as cool as possible. I use a spacer under the carb to reduce heat transfer. On one car it is a phenolic spacer, on another it is a stack of gasket, metal spacer (looked like a larger gasket and stuck out like a motorcycle cooling fin), gasket, metal spacer, gasket, metal, etc etc. There were several in a stack under the carb.
I don't remember where I bought that from, but it used to be commonly sold in the 1970's as a carb insulator.

A cool air intake usually makes a big difference on most cars I have had. Not just a performance boost, but also the benefit of esaier starting in hot weather. I used to put a large (3 inch I think) heater air hose on the air cleaner snorkel and run it to the cooler air in front of the radiator behind the grille. More often than not, I had to cut off the tapered snorkel "snout" coming out of the air cleaner to get a larger opening for better air flow, and something to attach the hose to.

I always blocked off the heat riser passages under the intake manifold, and threw away the heat riser valve that would get in the way of the exiting exhaust gasses. That kept the intake manifold cooler. No bad effects at all except for a few minutes extra warm up time ONLY in the coldest part of the winter. It helped the engine performance on all but first few minutes on the coldest days.

I have never had any vapor lock problems (somewhat different from a carb-boiling problem, but slightly related) on the cars which had a fuel return line back to the tank.
The only cars with vapor lock problems were the older ones that did NOT use a return line. The fuel would move slowly, picking up lots of heat along the way.

******************

Here's one thing I tried while I had the family on a long travelling vacation, and didn't want to deal with a long fix while on a trip-

On a low mileage late model car (in the 1970's) After a few hot-start problems away from home, I went into an auto parts store and picked up one of those $3.00- 4.00 silver-can fuel filters. The one I picked out was one with the usual inlet and outlet nipple for the usual flexible fuel hose, but this one also had a smaller third-nipple on the outlet side for use with a fuel return line to the tank.

Since it appeared to me that the filter had an orifice built in to the small outlet that would limit the amount of fuel being returned to the tank, I surmised that it probably wouldn't starve the engine by directing too much fuel volume away from the carb and starving the engine, but would still let the fuel recirculate just enough to keep a cool fuel supply instead of making it sit around and boil in the fuel line.

I put the filter close to the carb to make sure that nearly all the fuel got a chance to recirculate and stay cool, and ran a small return line to the rear.

It worked like a charm, so I left it on for the next several years. No more vapor lock.

That should work on just about any carburated car as long as you don't let the return line flow so much it starves the carb. Just enough bleeding of excess fuel back to the tank to keep a constant flow of fresh fuel to prevent heat-soak and boiling.

 

Dare-To-Be-Different...he's running a mechanical pump.

 

I know, but the return-filter-return-line trick I used was on a mech fuel pump car, so it should work on most.

... and this info will be read by guys with electric pumps also.

and keeping the carb cool is good for any engine.

 

oh and dont forget to change your oil..its probably deluted with fuel

 

Does it do this only when the engine is at full temp. What about when it has only run for a few minutes. Did the original setup have a return line. I would lean toward those who suggested a thick base gasket. Hope you sort it out.....soon, don't wreck your motor.

 

turn the car off, pull the air cleaner and look , listen.

Chances are the fuel is percolating causing the float to bounce and the carbs to flood.

Caused by heatsoak and todays crappy gas.

 

I second that...all my old cars now do it to some extent...it seems like the gas gets less stable every summer. I've slightly lowered the float in all, which helps some...spacers help too...

 

My daily does the same thing as well. Its loads up like a mother when I start it hot. I think next time I'm at Pep Boys I'll spend the cash on a plastic spacer and see if it helps.

Oh ya, EBrock aluminum manifold and EBrock carb. Never did it with the stock stuff, it just didn't run worth a damn.

 

Think on this, the cap om the tank is the vent, right, it lets air in the tank to make up for the gas you use. But some are not just a hole in the cap, they are a check valve. lets air into the tank but not out. So now the tank gets hot, the vapor pressure rises, it cant get out, it forces the fuel past the neddle and seat.
When the engine is running, it's using fuel at a rate that will keep this from flooding the running engine, but when you stop the engine, no fuel use, it forces past the neddle and seat.

Try leaving the fuel cap loose when you shut the engine off hot, see what happens.

PM me if this works and I'll send you my address to send the beer to

Frank