Need help with flooding after engine is off.

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Dusterdude72

Dusterdude72

IN MOPAR MUSCLE MAGAZINE
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Hey guys ,

Looking for some input on this issue I have.

so I was having a rich running condition for awhile and I finally got a pressure gauge and seen I was running 9.5psi from my pump to the carb. so I picked up a holley regulator and installed it and dialed it down to 6.5 psi. Car runs great and the rich issue cleared up alot.

however....my new issue has been that after I shut the car off. I can get out and look under the hood at my fuel pressure gauge and see it still holds the 6.5psi pressure in the line. and it takes about 20 minutes or so before that pressure leaks back down to 0psi.

the issue is that since I installed the regulator I can smell gas from my carburetor. And after it has been running and then shut down and left to sit for more than a couple minutes it is hard to start. it will crank over a few times before it finally starts up.

what I think is happening is the pressure in the line is holding after the engine has shut down and the that pressure bleeds fuel off down the carb which in turn floods it out a bit and makes for a hard start.

so what I tried today was installing a return line. on my regulator I have 1 inlet and 2 outlets. I have my pump going to the inlet and I have one outlet plumbed to the carb and I plumbed the other outlet to the return line that runs to the tank.

by doing this I solved the issue of the line holding pressure after the engine has been shut off, and I solved the issue of the gas smell and the hard start issue seems to be gone aswell. BUT now I can't read my fuel pressure gauge (its bounces all over the place as if its reading each individual pulse of the pump). and the other issue is that by giving an additional path for the fuel to escape I dont think the pressure at the carb is correct any longer. when I first fire it up it wants to stall and the idle is sporadic and I have to crank the fuel pressure way up just to clear the idle up some.

so my question is.....what do you guys think is going on and what suggestions might you have for me?.

it ran great with just the fuel pump hooked to the inlet and one outlet going to the carb and the other outlet blocked off. my complaint with it set up that way was the fuel smell and the hard start.

Thanks in advance for any help guys.
 
Could be a fuel boiling issue, a return is a good idea, but a .020 or so restriction would eliminate a fuel pressure supply problem, while allowing the release of pressure when the engine isn't running..
 
I dont think its a fuel boiling issue. Back when I had the pump ran directly to the carb I never had issues with fuel smells or hard starting. it just ran rich and had to much pressure so I went ahead and installed a regulator.
 
70aarcuda said:
what kind of fuel pump is it>?
Click to expand...

factory style mechanical fuel pum. airtex brand. I was surprised to see it was pushing 9.5psi being that it was just a factory replacement pump and nothing performance or high pressure.
 
Keep the return line, just install a .020 or so restriction in the return line. also will alow some fuel to circulate through the lines, keeping the supply side a touch cooler as well
 
and what would I use to restrict the fuel flow in the return line? and where abouts should I install it? (cut the line and install it or is what your talking about something that can be installed in a fitting at the regulator or something.

I get what your saying though. if I could restrict the flow of fuel that goes through the return line it would increase and steady out the flow of pressure that goes to my carb.

I also thought of something similar to this earlier today. something like a shut off valve installed in the return line and leave it opened just a hair...enough so that some fuel can escape but without it sending a rush of fuel down the return line and messing with the inlet pressure on my carb while running.
 
just take something like a bolt.... or a piece of brass, use a pin drill to put your orfice in it... then just shove it in a section of your return hose that is rubber
 
An easy way is to use a Wix 33040 or 33041 filter -- 5/ 16 and 3/8 -- which has a built in 1/4" return line fitting with an orifice
 
quick update guys.

today I pulled the brass fitting out of my regulator that my return line connects to. I tapped some threads into the backside of the opening on the fitting and threaded in a brass block off with a hole drilled in it about 1/4" in size. Fired it up and still had the same issue. fuel pressure gauge just before the carb was bouncing all over the place. So I took it back apart and I installed another plug but with a hole about the size of 1/32" pretty tiny hole. reinstalled it and fired it up. Checked the fuel pressure gauge and its STILL bouncing all over the place. it didnt even slow down the rate at which the gauge bounces. I thought that a hole as small as I installed in the return line would have atleast steadied out the pressure readings at the carb.

so now im not sure what I should do....I cant get an accurate/stable pressure reading at the carb with a return line (even with it restricted down in size). And if I do not run a return line I get the hard start issue do to pressure holding in the line between the regulator and carb after engine is off and then it bleeding out through the carb and flooding it.

I also thought of that wix filter with the return port but it seems asthough I would still have the same issue (fuel having an alternative exit and giving a funky pressure reading and pressure stability at the carb).

yes I am sure I could run it PRE regulator which would give me a fuel return....but would not solve the issue with the pressure holding in the line post regulator.

also I dont think I mentioned it but I DO have an insulator gasket between the carb and intake which should help if it were a issue with heat soak.

any ideas guys?.
 
Can you diagram the layout of your system? Must be something we are missing here.
 
dont mind the diagram skills or lack there of lol. I did this up real quick in paint to give you an idea of the set up.
 

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If the fuel pressure is being bled off through the carb on shutdown I think you are getting debris trapped between the needles and seats keeping them from shutting and sealing completely when the float bowls are full. What kind of carb are you running, Holley or Edel/Carter? I know on my Carters if the fuel filter goes bad and allows debris through to the carb it will act exactly how you are describing; in fact when I had this problem I could look down the carb throats and see fuel dripping from the boosters. New fuel filter fixed the problem; make sure you use a metal filter too, not the crummy plastic ones as they eventually warp from underhood heat.

Also if you are running an Edel/Carter without a plastic spacer it's pretty much guaranteed the gas will boil off in the bowls esp. when sitting idling in traffic or heat soaking upon shutdown. When that happens fuel vapor fills up the intake and carb throats making an over-rich condition on hot starts which is why you need to crank it longer. I've just learned to live with it on my Duster as I currently don't have enough room to run a carb spacer on my 360 with the air-gap intake and stock hood.
 
MOPEkidD-3 said:
If the fuel pressure is being bled off through the carb on shutdown I think you are getting debris trapped between the needles and seats keeping them from shutting and sealing completely when the float bowls are full. What kind of carb are you running, Holley or Edel/Carter? I know on my Carters if the fuel filter goes bad and allows debris through to the carb it will act exactly how you are describing; in fact when I had this problem I could look down the carb throats and see fuel dripping from the boosters. New fuel filter fixed the problem; make sure you use a metal filter too, not the crummy plastic ones as they eventually warp from underhood heat.

Also if you are running an Edel/Carter without a plastic spacer it's pretty much guaranteed the gas will boil off in the bowls esp. when sitting idling in traffic or heat soaking upon shutdown. When that happens fuel vapor fills up the intake and carb throats making an over-rich condition on hot starts which is why you need to crank it longer. I've just learned to live with it on my Duster as I currently don't have enough room to run a carb spacer on my 360 with the air-gap intake and stock hood.
Click to expand...

Everything is new, carb is a new summit racing 750cfm carb.....it doesnt have the issue when hooked directly to the pump....so it seems like if it was an issue with debris lodging that it would also do it hooked up that way and not just when hooked to regulator.

It also has a new filter which is a steel case filter.

I can start the duster up cold....let it run a couple minutes (not even to operating temp) shut it down. go to try and start it 5 minutes later and it will have the starting issue due to the pressure being held in the fuel line. so I dont think its an issue with the fuel boiling.

something to do with the pressure holding in the line and bleeding off after it is shut down. I either need to figure out how to stop it from bleeding the pressure off down the throat of the carb or I need to relieve the pressure so that it doesnt have the pressure issue. The problem is...each way I hook it up comes with its own set of additional issues lol.

sure I could leave it hooked up and deal with having to crank it a little bit to get it to start but I dont want to have the gas smell under the hood after sitting and I dont want to labor the starter and battery over time either.
 
dont understand this boiling of gas ...been using the same eddy 1406 for almost 10 yrs in LAS VEGAS, with no spacer under the eddy air gap...performer or performer rpm that the carb has been on.....many times i have gotten in the car..and the engine temp gauge is at 140..and it has not been started yet..

take the needle and seats out..blow them out with some carb or brake cleaner...
 
Have you got the regulator return hooked to the factory vent line? Did you remove the valve at the engine bay end of the vent tube?
 
67Dart273 said:
Have you got the regulator return hooked to the factory vent line? Did you remove the valve at the engine bay end of the vent tube?
Click to expand...

No I installed new line from the regulator all the way back to the tank. And as I mentioned earlier I have also tried adding multiple restriction orifices into the head of the return line and still have the issues with not having a stable pressure reading at carb.
 
You ever think that there might be something internally wrong with that fuel pump....

according to airtex it is suppose to max out at 7.5 psi....
 
I noticed that aswell. But the pump I had on it before this pump which I believe was a carter also ran about the same pressure . so I just assumed they under rated the pumps a bit.

even so...I dont see how that would come into play. The regulator is between the pump and the carb . My issue is the regulator holding pressure in the line between it and the carb with the engine OFF.

If I do not run a return line and just run my fuel line from the pump to the regulator and from the regulator to my carb. my fuel pressure gauge is as steady as can be....doesnt pulse in the least bit. But with it installed this way I have the issue with it holding pressure in the line and dripping fuel down the carb with the engine off and flooding it.

it I run the return line I can get rid of the flooding issue but in exchange I cant get an accurate fuel pressure reading and I am not sure how stable the pressure is at the carb because of it.

its a bit of a tricky issue so far lol. Trying to come up with some ideas on what I can do to resolve it.

for the heck of it I may pull the needles and seats tomorrow just to check them but I doubt there is anything lodged in them. fuel line is all new,filter is new,pump is new,carb is new,gauge is new,regulator is new and tank has been cleaned. so I am not sure where any debris would have came from. but ill check anyhow just for the peace of mind lol
 
your retriction orfice is to large.. it needs to be small, real small, like the .020 I mentioned earlier..All you want it to do is bleed off the pressure when the engines off, if the restriction is to big, it will simply flow too much fuel all the time
 
70aarcuda said:
dont understand this boiling of gas ...been using the same eddy 1406 for almost 10 yrs in LAS VEGAS, with no spacer under the eddy air gap...performer or performer rpm that the carb has been on.....many times i have gotten in the car..and the engine temp gauge is at 140..and it has not been started yet..

take the needle and seats out..blow them out with some carb or brake cleaner...
Click to expand...
Could be the formula or the blend of fuel in your area, around here, when they change the blends winter/summer, you can absolutely tell a difference. Race fuel seems to NEVER have these issues, in my experience
 
I've got to give props to replicaracer. I went in town and had to do a lot of hunting to find a # 76 drill bit ( .020) but finally found one.

Ended up tapping threads into the outlet side of the fitting I'm using to connect my return line to the regulator. I then too an old edelbrock fuel jet I had sitting around and soldered the opening closed. And then drilled it out with the #76 bit. Then threaded it into the fitting and reinstalled it.

Fired it up and my fuel pressure gauge holds nice and steady while running and when I shut the engine down it only takes about 3 seconds for the pressure held in the line to bleed off down the return line!.

Good call and thanks for the tip. Looks like this little fix may have did the trick.

Here's some pictures of what I did invade anyone else ever runs acrossed this issue


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