Vapor Lock Issue

[Dean]

Ok guys I'm looking for new ideas on vapor lock issue here as I'm about out of them.

Truck is a 1985 K30 with a 572 big block in it.

I've done the following which has helped some but it is not completely gone as it has done it at least three times this year.

Spacer under eldebrock carb
GM shield under carb
wrapped gas lines
bigger radiator fan
cowl hood
open air cleaner element

The truck does have dual fuel tanks. Should I try a high pressure fuel injection pumps with that recirculating line? And put a fuel pressure regulator before carb? I'm not sure this would all help or not?

I'm open to any suggestions.......

Thanks

[Bullseye54]

One other thing,make sure you don't have a filter between tank & fuel pump.Was having same type of problem with Edel carb on my 68' removed filter & put one after pump no more problems.My 67' has a Qjet with filter before pump with no problems.

[storm9c1]

Originally Posted by Bullseye54

One other thing,make sure you don't have a filter between tank & fuel pump.Was having same type of problem with Edel carb on my 68' removed filter & put one after pump no more problems.My 67' has a Qjet with filter before pump with no problems.

+10000

And Eddys need more volume, not pressure. I couldn't resolve these problems without using a Eddy fuel pump. They are designed for high volume at 6psi (which is what an Eddy wants). Drove me nuts the first time I got involved with using Eddy carbs.

[Bullseye54]

I was just going to mention the fuel press deal,it caused a stumble off idle on mine.I put a summit press reg. on mine & took care of stumble.

[mstrav1973]

what about an electric pump as a primer to the mechanical pump on the engine? I had to do this on an LS6 454 I had in a truck and it solved my problems. I never confirmed vapor lock or that the mechanical pump couldnt keep up.

Matt

[Dean]

I only have an electric fuel pump (AC Delco) that is back in the frame. Should I put a Eldebrock electric pump in place of this one? Do I need more volume or pressure?

The only filter I have is up near the carb.

I'm not even about to turn the A/C on........that would make it even worse I'm sure. It is bad when it does this towing a trailer and no place to pull off. The steering and brakes are rough at that point..........grrrrr

[Shyguy]

Ah, now this kind of clears up some stuff when you say you only have an electric fuel pump. Vapor lock may not be the problem.

The fuel pump may be the problem. Is it close to the exhaust?

You could go with an Eldelbrock fuel pump and regulator with both mounted away from the exhaust or shielded from the heat of the exhaust.

Have you checked the condition of the pickup sock in the gas tank?

Just throwing out some ideas at this point.

[Dean]

Maybe I do need to move the electric full pump even further away from the exhaust.

Where would be a good place to mount this pump? Up in engine compartment? Not much room down by the exhaust.

The socks in both tanks are both new.

[storm9c1]

Volume is needed on Eddy carbs at no more than 6.5psi pressure MAX. Other carbs can put up with more pressure to keep up with volume. But not an Eddy. You can have less than 6psi, but you better make sure it pushes some volume.

I've had the best luck with using their own (Eddy) mechanical fuel pump (1721 sbc, 1722 bbc). It is a 110 gph unit that puts out exactly 6psi of pressure (no regulator needed).

If you currently use an electric pump only, make sure it meets these requirements. Does it already have a regulator in-line with it? If so, you just may need to upgrade to a larger capacity pump. If no regulator, you will have to find one that puts out 6psi at 110gph or more on its own (or add a regulator).

I also question how close your pump is to your exhaust.

[El Jay]

I hope my naivete' doesn't show too badly.

Are you sure it's a vapor lock and not fuel starvation because of an unvented gas cap(s)?

[Shyguy]

Originally Posted by El Jay

I hope my naivete' doesn't show too badly.

Are you sure it's a vapor lock and not fuel starvation because of an unvented gas cap(s)?

I should have thought of that, I had a problem with a motor home because the gas cap was not vented many years ago.

[cdowns]

are you sure your gas tank is vented well enough?
have you checked the pickup in the tank? i saw a real odd one once where the pump actually had enough suction to pull the bottom of the tank up and restrict the outlet.

[storm9c1]

Originally Posted by cdowns

are you sure your gas tank is vented well enough?
have you checked the pickup in the tank? i saw a real odd one once where the pump actually had enough suction to pull the bottom of the tank up and restrict the outlet.

+1. Check that too!!!!!!!

[Dean]

Yeah I guess I better check both gas caps too just to be sure.


I bet moving that fuel pump up to the firewall would be better.

[El Jay]

IIRC, electric fuel pumps should be mounted as low and as near the fuel tank as possible for optimum performance.

[cdowns]

yeah closer to the tank is better// if you suspect it's overgeat due to exhaust pie it's a real easy fix to make a heat shield out of a piece of aluminum and clamp it on the exhaust pipe to shield the pump from the heat

as far as checking gascaps just use the truck for awhile and as soon as you get out take the gascap off. if you hear a whooshing sound when you remove cap there's a vent problem with your tank

[Dean]

The electric fuel pump is about an inch from the exhaust. I do have a shield on the exhaust and the fuel pump/line is wrapped. This is driving me crazy......... I'll be checking the gas caps again too.

[Dean]

I'm a GM electric pump #2511589. It has 72 GPH and 6-8 psi.

[storm9c1]

Originally Posted by Dean

I'm a GM electric pump #2511589. It has 72 GPH and 6-8 psi.

As I said before, I had fuel starvation problems with Eddy's before esp on big blocks (which gets worse with heat and appears to be vapor lock but it wasn't). The only way to solve it was to replace the stock fuel pump (which was probably about the same flow rate as the one you listed). The Eddy pump puts out 110 gph @ 6psi, which seems to make an Eddy carb happy.

Either replace it with a higher flow unit (or do more testing if you don't want to throw parts at it). A test harness with a fuel pressure gauge strung through the passenger window should tell you if your current fuel pump can keep up. If pressure drops below 4psi under acceleration, you need a better pump. With that big block you have, I really don't think 72 GPH is enough for an Eddy. At least by my experience.

[piecesparts]

If you have a mechanical pump on the engine, do you have a return line from it, back to the tank? There is some vapor locking in the fuel line and I found that installing the return to it's normal design helped my truck. I am using the Edelbrock fuel pump that has the removable plate on the bottom. I installed the plate with the optional plugs and then used one of the ports for the return outlet. Make sure that you use an orificed hole to keep the fuel pressure up on the carb. Another avenue would be an electric pump for better fuel feed. Have you looked at changing your fans to electric and getting a better airflow through the radiator?

Which carb spacer are you using? I have the phenolic 1" spacer on my stroker engine and it definitely helped.

[Dean]

I do not have a mechanical fuel pump on this engine just the electric one. Sounds like I need to look into the Eldebrock pump or maybe a return line.

My carb spacer is phenolic. Everything has helped a little but it is still there.

[piecesparts]

Originally Posted by Dean

I do not have a mechanical fuel pump on this engine just the electric one. Sounds like I need to look into the Eldebrock pump or maybe a return line.

My carb spacer is phenolic. Everything has helped a little but it is still there.

Since you already have an electric pump, I would keep it. I would put a pressure regulator close to the engine and let it have a return line to the tank. That would keep the fuel to the carb a lot cooler. The mechanical pump can absorb heat from the engine and headers.