Fuel flooding out of Edelbrock carburator

[The_Handier_Man1]

From: oldRoadRanger_al  (Original Message)
Sent: 11/7/2005 4:44 PM

Here's a strange one I have not run into, wondering if any of you have.

On a trip a few months ago when it was hot out, the beastie ('77 Dodge MB400 chassis 440 motor) started running really rough while at a 60 mph cruise on a two lane out in Wyoming. I pulled over and she died immediately. Smelled gas so I removed the doghouse and air cleaner. Cranked her and it finally fired after a bit. Gas poured out from the metering rod covers on the Edlebrock and other spots flooding like mad so I figured the needle(s) was stuck. Took the carb top off and apart, all was clean, not a speck of anything to hold the needle open. The floats are set properly too.

What I did notice and never have encountered in my 4 decades of shade tree mechanics is when I pulled the fuel line from the carb there was tremendous pressure. I mean pressure! fuel shot all over and it sounded like I disconnected a fitting from an air hose. There had to have been 30 psi... or so it seemed. The fuel pump is new and was fine till then. Could this be the opposite of vapor lock? Could the fuel be boiling in the line from the pump to the carb due to radiant heat from the exhaust manifold building up this pressure? Have any of you guys run into this in hot weather and has anyone installed a pressure regulator at the carb to fix.

It continued to flood out intermittently during the 4 hours home. Especially when you worked it, like up a hill or pushed too fast on those empty roads, making heat.

I never have seen this flooding from overpressure before, and it seems to me that what it must be. Boiling in the line after the pump with nowhere for the pressure to go but past the needle & seat. I'll install a regulator and insulate the lines.

Any thoughts?

Thank you!



From: cooneytunes
Sent: 11/7/2005 9:36 PM

That's a new one on me.....I have a 76 440 and it was prone to vapor lock from exaust using the mechanical fuel pump...so now I'm using an electric fuel pump...solve the problem.........My 76 has non-vented fuel caps, I think in 77 they went to vented fuel caps.....it might be possible that the vent in the fuel cap is plugged up causing an excessive build up of pressure in the tank....and  / or the line going to the charcole canister is plugged up and not allowing it to vent properly....I'd try opening the fuel filler cap if it happens again..if it belches a lot you've got too much pressure in the tank ...max pressure should be about 7 lbs,,,if you could get a pressure gauge on the fuel line you;d know.....I could be wrong, but don't think your problem is being caused by excess heat in the line....sound more like an exxcessive pressure build up caused by something  failing to vent..........air does some funny things with liquid inside a closed line or piping system...Keep us up to speed at what's happening with it...
Timmy



From: denison
Sent: 11/8/2005 7:01 AM

Make sure the fuel lines are not in 'sight' of the exhaust manifold or exhaust pipes. There should be something in the way between them to stop radiant heat. I had vapor lock on my 413 until I put some pieces of aluminum flat sheet between the lines and the manifold; in such a way that nowhere was the exhaust system radiant heat able to 'see' the fuel lines or fuel tanks.
And when I had vapor lock, it was due to the temperature of the fuel before it reached the fuel pump. My fuel pressure would go to zero. This was above 8000 ft and about 95 in the shade, much hotter on the sunny black macadam pavement. I dont think the heat downstream from the pump was a problem. In your case I would check the pressure from the fuel pump. I think it should be 9 psi. maximum.



From: spudboy
Sent: 11/8/2005 10:27 AM

My 72 D22 with a 413 had the same problem.  After running for about two hours in hot, high elevations, I would slowly lose power to the point that it would only run with the dog-house off, floored and no air cleaner.

I now have it set up with venting gas caps, an electric fuel pump and routed the fuel line on the outside of the frame and as far from the exhaust manifold as possible, new 360 degree air cleaner...problem solved.

-Spudboy



From: oldRoadRanger_al
Sent: 11/8/2005 4:40 PM

Thanks for the comments.
I will insulate the lines, install guards so the line can't "see" the ex. manifold and plumb in an adjustable pressure regulator.
The pump is not faulty it's pressure is normal. Gas cap is a locking one that fits so loose I worry water will get in, pressure will not build up. Seems like that would be it though. My brother who was with me on that trip (fishing in Yellowstone) is a 25 year ASE Master Mechanic and he is scratching his head. That's why I figured I'd post to see if anybody else has this strange problem.



From: ClydesdaleKevin
Sent: 11/15/2005 2:26 PM

Woah!

Are you all implying that a "vented" gas cap should still have some pressure, either positive or negative, when removing the caps?  Are they made like radiator caps, with specific psi pressure relief?

I ask this because I thought my new caps were the problem when we encountered fuel problems on our trip, and I altered them to vent freely.  It wasn't the problem after all, but now its got me thinking...should I get new caps to replace these ones that I altered?

Kev



From: denison
Sent: 11/15/2005 3:04 PM

   A vented gas cap is essentially a dust and insect cover, and to keep fuel from splashing out on bumpy roads - holds no pressure.   Of course even the non-vented caps are supposed to relieve when the pressure gets above some level - so the tank wont rupture.   
   Assuming your modfications dont result in them spilling gasoline from a close-to-full fuel tank when you bump over bad sections of road you can keep them.  It would be unsavory to waste petroleum resources.
   By the way Kevin, we are in Mercedes TX for the next few months, using a library computer, since my linux based laptop isnt agreeable to dial from my father-in-laws house to my netzero account.



From: ClydesdaleKevin
Sent: 11/16/2005 5:20 PM

How far is that from Houston, Dave?  Any chance you and the missus can make it down here this weekend to come to the last 2 days of the Renaissance Faire?  Right after this weekend, we are headed to Virginia Beach and then Richmond for a couple of small Christmas shows, and then down to Florida for the three winter Ren Faires that we work down there.

Kev