38 Weber / fuel pressure question

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Apr 9, 2009
Mason, Texas
What are the symptoms of a 38 Weber receiving too much fuel pressure?

I got into a bind/stranded and had to replace my fuel pump with an electric pump. Now, when the engine is warm, it will die at idle (700 rpm). Cranks up fine when cold... runs great until I stop :bang:. All ignition parts are new. Engine is a 74 f.5, and runs STRONG! Just replaced the electric choke with a manual, thinking that was the problem. Now I'm thinking of adding a pressure regulator.

No, not going back to the mechanical pump. Planning a tbi on the new engine I'm building.

Please chime in if you have some insight. Thanks! :popcorn:
Webers use very low pressure, probably down around 3 psi, you could have a 5-7psi, 15 psi, 35-40 psi, or 60-100 psi pump?????. If you are thinking TBI you might want to look at ebay #251530256646 Adapter, or #261715893989 or #251595965586. If you are not interested in any of that, then talk to me about the TBI installation instruction manual.
Thanks Downey! I have purchased most of these items from you... plan to follow your lead with my tbi!

What are the symptoms of too much fuel pressure? I've been researching, but have not found much on the subject.

My current electric fuel pump is supposedly rated at 2.5 - 4 pounds... but it came from AutoZone, so who knows. I don't have a pressure gauge. I replaced the carb gaskets a few days ago to fix the vacuum leaks. Now the gaskets are saturated and are leaking again. :bang:
Install a fuel pressure gauge and then you will know which way to go. Everything else is speculation.
Go find a CJ series fuel filter or similar - it has a bypass built in that will bleed off pressure if your tank has a return line . Generally , over fueled Webers will die at idle or at least chug pretty bad and clear right up when the throttle is opened . It doesn't make sense to run good cold but that could be the pump being sluggish .
Thanks for the responses!

I'll buy a tester today and get an accurate fuel pressure reading.

Sarge... What year CJ filter? I'm completely ignorant when it comes to jeeps.

I forgot to mention... when the engine dies, and I attempt to restart, it will start for a brief second (literally one second), die again, then make a gargling/boiling sound, along with a mild backfire. Again, it only does this when the engine is warm (180 degrees).

Any thoughts?

Thanks again!
If you want to verify - next time it dies just pull the air filter off and look down the carb throat , if the needle is being overrun it will be dripping fuel out the main venturis . Just pick a late 70's fuel filter from a Heep , almost all parts stores carry them .
Hey Sarge, something like this?

Your symptoms say flooding at carb/intake, but back fires are normally electrical, so might want to sniff around in that area.
Hey Sarge, something like this?

View attachment 1012609

Yep , that's the animal . I'd still verify it's flooding with a visual check in the throats and make certain it isn't a choke issue or something dumb . Fuel pressure gauge is the best way to tell , the standard issue vacuum/pressure gauge is handy to have for these older trucks and worth having around .
My 76 came to me with a Webber carb and an adjustable flow regulator in the fuel line. I thought it was because it was operated at high altitudes ( vehicle came from Colorado and was used in the High Country) now I know why it has the regulator. You learn some good stuff hanging around here.
I'll warn you in advance - unless it's an older regulator none of them work very well with the Weber , it needs a steady low 3psi or even less offroad . All the newer low-pressure pumps are about as reliable as a Yugo , although there are/were exceptions . Best route is to use the stock mechanical pump and either tap the carb's inlet head (very tough to do it right without wrecking it ) or use an inline bypass filter . I have built brass bypasses that had provisions for using a Weber main jet to regulate the flow and they worked the best . There are bypass type regulators but decent ones cost more than a new carb . Just be careful about placement of the filter and heat , route the return one way or another back to the tank - best and easiest solution .
So far so good Sarge truck runs strong as it is currently set up. I'm pretty sure this is an older regulator. It is identical to the one I put on my 74 mini truck when I changed out the electric fuel pump and it was producing too much pressure for the stock Mazda carb back in the early 80s. I will keep an eye on it and change to a by pass filter if I develop any problems.
Thanks for all the input.

Yesterday, I bought a fuel pressure tester. This morning I hooked it up and tested... the tester measured 6.5! I assume this is my problem.

I ordered a Holley 12-804 adjustable fuel pressure regulator from Speedway. The factory setting is 2.7, but can be adjusted from 1 to 4 lbs.

I'll post an update after the install later this week.

Thanks again! :beer:
No offense , but those regulators don't work much better than the crappy dial-types from Purlator . It really needs an open or slightly restricted flow to the return side of the tank . Some have had luck with that reg , most haven't including myself when I ran the 40DCNF on my Sami .
I installed the Holley fuel pressure regulator , along with a Marshall gauge. I have the regulator set at 2.5 lbs. The Weber still floods after the engine is warm. I don't understand this at all. Can someone clue me in?

Okay Sarge, I admit defeat, and will give your bypass fuel filter a try. Do I install the bypass filter before the regulator or after?

Thanks for the suggestion/advice!

Stick to the Viton float valve , they handle vibration better . Do you know the correct procedure for setting float height by hanging the float by it's pin the measure ? Do not measure it with the top air horn upside down , it compresses the internal damper spring in the float valve and sets the fuel height way too high . The air horn needs to be held vertically .
No sir. Never adjusted floats before. I've read quite a bit in the last few days about it, as well as watched a few you tube videos. I pretty sure I can do it. I'll give it a try this evening. Any suggestions for measuring? Will calipers work?

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