fuel problem...flooding

[terrymac]

I'm having trouble with fuel gravity bleeding and flooding the engine to the point it will hydro lock if left with the shut off on over night. At first I thought the floats were too high and set them down, seemed to help it run better but it's still running rich. I pulled the needle valves and cleaned them. I again thought I had it resolved. Thought maybe I missed some dirt on the needle valve seats so turned the fuel off and run it out. Thinking this would flush the needle valves just in case. It was like a gyser fuel everywhere when I restarted with the fuel turned back on. I'm stumped, I would have thought the needle valves would hold off gravity
Terry
Opps ... I'm running 2 500 cfm eldebrock carbs with manual chokes. These were new from Speedway

 

[dovehunter79]

how much PSI are you running into the carb? You could be running too much PSI from the fuel pump into your carb.

 

[RPM]

It has to be a float level thing or the needle valves. Can you tell which carb is doing it?

 

[409T]

Had the same problem. It was dirt in the needle and seat assembly. Got in there by hooking up the new fuel lines without blowing them out first.

Jeff

 

[just for fun]

Started to talk about fuel pressure and thought not a player when the motor isn't running! Duh (on my part)Still I'd check it just to make sur over pressure hasn't damaged the rubber tip on the needle. You are running a fuel filter just befor the carbs right? the thing of it is where is the system picking up enough trash to keep messing with the carb needle and seat. Block off one carb to try and narrow it down

 

[railroad]

Make sure your gas tank is vented. It may be holding increasing pressure against the needle and seat. You may be able to remove the cap after some run time and determine if there is pressure in the tank. If you are running a metal fuel line, make sure it is not cooking somewhere along the way.

good luck,

 

[GT63]

I have heard of this happening if your fuel tank sits higher than the carbs. That's why I have a fuel shut off valve right below the tank.

 

[terrymac]

I've ordered new needle valves and seats sould be here on Monday. I really think that they should hold off gravity when the engine is shut off but I did put a shut off in the line when I built it. I'm going to play with the float levels some more in the mean time but I think that as long as the foats are low enougn that the fuel doesn't actually run out the top it should shut it off anyway
I'll keep you posted
Terry

 

[tnoftsger]

I have heard of this problem many times before. A shutoff valve is a good idea, however any needle and seat should be able to with stand 5 psi.

so with the formula:

Head in feet = (psi*(12^2))/Specific Gravity of Fuel in pounds per cu. ft.
or
Head in feet = (5*(144))/58 lb/cuft

Head in feet = 12.41

So unless the fuel level in you tank is 12' above the needle, it SHOULDN'T allow gas to slip by and flood the motor.

All of that assumes that the tank is vented and not under pressure.

That's about all the useless knowledge I can type up at one time.

 

[terrymac]

Spoke to edelbrock's tech line yesterday. I think I'll write that off as a waste of time. On hold for at least 10 minutes before I got to talk to anybody and then before I even finished describing my problem he was going off about High fuel pump pressure holding pressure in the line. After I finally made him understand what was going on he said "Oh I've heard of that you'll need a residual check valve, we don't sell them and I don't know where you'll find one or who makes them" I am going to check my fuel pressure over the weekend just in case and go from there. He did say that it wasn't uncommon that mechanical pumps get up over 10 lbs. I've never run into high pressure with a stock pump before but there is always a first I guess.

 

[Screaming Metal]

Sorry guys....been gone a while......We kicked some major ass but blew a engine doing it.......Guess thats what racing is all about.............

Fuel leaking past your seats is caused by:
1. Too much pressure
2. Something holding the needle off the seat:
A.Trash
B.Seat distorted
C.Something not allowing the needle to seat, like say, the float
assembly put together wrong
3. Fuel bypassing the saet all together..........

Usually fuel flowing past your diaphram pump is caused by the pump being weak. 'A mech. pump can't push fuel past a electric.....but a electric can push it past a mech.' is something a old mechanic once told me........seems to be true.
Even if your tank is to the valve covers, you'd have to have a siphon action going on.
Even if your engine is shut off.....you should have very little fuel going thru your pump.......remember there's a diaphram, spring ass. in there that acts like a flow control valve. If the fuel gets past that, you'd have to push hard on the float and seat to get fuel past that. At least 10 PSI, I would guess.

Sounds to me you've got a leak inside the carb......like a check valve thats come unscrewed, a seat that has come loose, a welch plug leaking, something to that effect. Or your pushing way past 10 psi, or possibly even a screw in your lower floatbowl is dripping.

Take your time.....eliminate one thing at a time.......pay attention to details........it should show itself fairly quickly.......

 

[Ted Brown]

Just my two cents worth.. I have seen may too many people use Teflon tape on their brass and steel fittings, a very big no no, as that gets into your system and causes a ton of problems... NEVER use teflon tape on flared fittings of any type.. :lol:

 

[putz]

I agree with Ted.Teflon tape should not be used on anything with seats or switches that stop the flow use teflon thread sealer in liquid form if needed. Not pipe sealer either.

 

[Humidi-T]

He did say that it wasn't uncommon that mechanical pumps get up over 10 lbs. I've never run into high pressure with a stock pump before but there is always a first I guess.[/QUOTE]

My stock SBC pump puts out 9-10 psi on the gauge at the carb.

 

[terrymac]

I guess it's eat crow time I checked the pressure and it was 15 lbs so I installed a regulator then followed edelbrook's recommendation lighter step springs on the on the metering rods. Flooding problems seem to be all gone. I don't really understand though. Why would the higher pressure affect the needle valve well after the engine was shut off. Mechanical fuel pumps are from an era when everything was carburated and this is the first time I ever ran into this problem using one.

 

[Screaming Metal]

I guess it's eat crow time I checked the pressure and it was 15 lbs so I installed a regulator then followed edelbrook's recommendation lighter step springs on the on the metering rods. Flooding problems seem to be all gone. I don't really understand though. Why would the higher pressure affect the needle valve well after the engine was shut off. Mechanical fuel pumps are from an era when everything was carburated and this is the first time I ever ran into this problem using one.

Hey.....Holley used to make a full on racing mechanical pump that'd hit 35 or 40 psi when the rpm's go up! But that was back in the 70's/ early 80's. nothing to be embarrassed about.......just think on it as a quest for knowdledge.....thats one less question that has to be answered.......

by the way....if its a over the counter Holley of the mild performance kind....shoot for about 4 to 6 psi....mount a pressure gauge at your log.....(they make your setup look cool).............

 

[Screaming Metal]

Just think of the area just ahead of your carb to the fuel pump being a high pressure zone. That needs to hold pressure for a while after the system is shut down......remember....you ahave a diaphram in the thing, along with springs......acting as a one way valve. If the pressure would bleed off just when the engine is turned off.....the pump would have a tendercy to loose prime.

That needle valveis on a angle and the seats aren't the hard brass variety that used to be in carbs back in the old says.....because of the angle they'reon and the float mechanism.....they can't take a lot of pressure.....plus they're steadily being opened and closed.....fuel sloshing, etc....

If you have the coated tips in your carb.....watch what kind of fuel you run......gasahol was bad about making them distort slightly..............

This is designed this way so after lets say 3 or 4 weeks.....gas evaporates.....you'll have a full floatbowl and some fuel in the line to help pop things right on off on the first touch of the key!........Ted and Brucer could probably add more........

Say....where's PasadenaHotRod........is he OK????????

 

[blownt]

needle and seat will not stop gravity if your tank is higher than the carbs. Fuel, like water will seek the lowest level. And it will go right thru needle and seats.

When I first built mine I had a tunnel ram with 2 600's. Could never get it running right so put on a single hi-rise and 850 carb. Put it in the garage after driving. The next time I opened the garage a few days later there was a STRONG odor of gas. I looked in the gas tank and it was empty and all the gas was in the oil pan. Since the tank was now higher than the carb it siphoned thru the line, thru the carb, thru open intake valves, past the rings and into the oil pan.

Added a small brass ball valve before the fuel pump. Just remember to close it when you put it back in the garage or you will have another oil pan full of gas. Also remember to open the valve or you will stop a block or so from your house.

Also drain and replace the oil. Run it a few minutes and replace it again. A SMALL amount of gas in the oil will wipe out a set of bearings and a crank in a hurry. I had to get a new crank when I rebuilt the motor after that experience. Went with the blower and that stopped the problem. Carb were much higher than the tank.

After I get mine back on the road after my new modification I definently will not worry about gas siphoning.

 

[Ted Brown]

How do you see around that scoop?? Something that is just for looks and gets in your sight path of people, I would think would not be a good thing.. ?? Drive safe, that would get ME a ticket... :ciao:

 

[Screaming Metal]

How do you see around that scoop?? Something that is just for looks and gets in your sight path of people, I would think would not be a good thing.. ?? Drive safe, that would get ME a ticket...

Me too Ted.....I got a warning ticket once driving my 421 Pontiac with my 8-71 and twin 780's on it.........'Obstruction of view' was the wording......about 5 blocks away and 30 minutes later....I was given another one.....'exhibition of speed'........I just called it a burnout......my young but stupidier days.............