Fuel pressure regulator

[oprn]

I am having a bit of a puzzling issue with my engine. It seems to be getting richer and fuel mileage is going down. Background:


type 4, fresh engine with maybe 800 miles on it.

Was getting 29 mpg but now down to 25 mpg. Smells rich when following it on the highway. Used to cruise at 14.2 to 14.5 AFR now is in the 11.8 to 12.3 range. exhaust pipes black inside O2 sensor black. AFR at full throttle unchanged at 12.5 to 13.2.

Italian Weber 40s idles were 52, changed to 50, no real improvement.

This is the fuel pressure regulator which if I recall was factory pre-set at 2.5 psi, now at 3.4psi, tried to get it lower but 3.2 is the lowest it will go. Literature says 1 to 4 psi range. Carter electric pump.

Is this regulator the problem?

[madmike]

Yea I think quality control on these went out the window lately I swapped to an 'Aeromotive' return style with boost ref
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[jpaull]

Have a guage mounted?

I would first check the floats. I run idfs at 3psi with no regulator and the floats can hold that over night.

[raygreenwood]

[Maddward]

I had a mix up with one of those Holley regulators. Part number 12-803 is for 4.5-9 psi and 12-804 is for 1-4 psi. They are the same exact regulator externally, they just use a different spring. Take the top off the regulator and check. A plain colored spring is the higher pressure one, a spring with red paint marks on the coils is the lower pressure one.

[slalombuggy]

Are you using a return line to the tank for excedssfuel or just deadheading it to the carbs. I tried one of these with no return line and got really frustrated I went to a Maripassa regulator from CB with a return port

brad

[Mark Evans]

I ran the Holley type with a gauge mounted on the supply side and could dial it in perfectly.
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[APPLEGREENVW]

Here is a great video on fixing the issue with the Holley regulators.

https://www.youtube.com/watch?v=vRYOW9WLHLs
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[oprn]

I was not aware this was a Holley regulator. It was not advertised as such.

No it does not have a return line to the tank, it is intended to run "dead headed" at the regulator.


Foolish me I took it for granted that factory set would be fine. My bad for not checking it on install.

It could be that a bit of something is stuck under the seat too. Time to investigate further.

Thanks for the video! Same regulator as his.

[oprn]

[[email protected]]

worst case you can clip a coil off a stiff spring to soften it up enough to get adjustment.
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[modok]

I don't think I ever had a similar problem with the fuel pressure.
I've run float needles and seats far uglier than those, but they worked Ok. with faucet or carter 3-4psi pumps or stock pumps. I've discarded floats that were too heavy, and needles/seats that appeared too worn, but i never had either part actually fail for me.

Not to say that isn't possible, but, if it takes those things a LONG time to wear out, so, it's unlikely for them to act up "suddenly" unless they get something stuck in them, like a fiber strand from a hose, which can happen. or something STRANGE has occurred.

Is it possible.... when you had them apart, you swapped the needles from one to the other? or the seat assembly or a jet isn't fully tightened? Just wild guess.
I've always been a little afraid of that, as far as, if the last guy mixed up what needle goes to what seat, you'd have NO to way to know, nobody would.

What does the fuel pump put out unregulated? I have no experience with that unit, but just from the size of it I'd expect you'd need several PSI pressure drop across it to work right, with such a small diaphragm.

[modok]

Fuel pressure specifications, from weber maunal, translated from italian/metric to english

scale range, for fuel supply feed pressure measurements; may also be of the wide scale range type measuring,also depression(mano-vacuum-meter).
It must be ducted in proximity of carburettor connection by meansof a plastic tube so that the instrument may be kept in driver's compartment and give pressure readings during vehicle operation at high road speeds when pressure drops are more likely.

For the majority of Weber carburettors, normal fuel feed pressure values are the following:

-

Maximum pressure: 0.3 kg/sq.cm
(4.2 psi)

measurable when engine operates in the transition (progression) or idle speed stages


-

Minimum pressure: 0.2 kg/sq.cm
(2.8 psi)

measurable on the road around top rated vehicle speed.

[Maddward]

The Holley regulator springs aren’t that expensive if you end up needing one. I just recommended checking because I was shipped a 4.5-9psi version when I ordered a 1-4.

https://www.holley.com/products/fuel_systems/fuel_...rts/12-807

[oprn]

No I haven't had the float valves out.

I intended to check the fuel pump pressure without the regulator but forgot last minute in my excitment to try out this spring.


The spring looks like it came out of a flashlight. The one that puts the pressure on the batteries. A bit shorter and somewhat softer. Backed off it gave me 0.8 psi so I cranked it up to 2 psi and put it all back together.


Out on the road I'm back at 14.2 AFR at cruise so it did make a difference and we should be back up to 29 mpg I'm thinking. Idle is much smoother too even though I didn't touch the screws.


I might experiment with dropping it a bit more. The engine will tell me on the uphills when I reach the volume limit. I should see it on the wideband too.

[oprn]

[oprn]

[modok]

There are a lot of factors. The needle and seat size, viton tip or metal, the fuel pressure, all may require different setting.

Even, how the engine vibrates can make the floats work better or worse, and nobody really knows which way it's going to be.
I've always thought that's why the Kadrons are the way they are, but I don't know for sure.

A lot on guys on here advocate 11mm float level, in the usual IDFs, or even 10

I always set them lower, about 12mm from the gasket, for various reasons but mainly just seems to work for me.

But.....it does not have to be exactly anything, nor does the fuel pressure, if it's working fine.

[[email protected]]

On decel MAP is very high, pulling more fuel through the idle circuit than when at idle (lower vacuum). Back in the day that's why early emissions engines had a vacuum pot which prevented the throttle from fully closing when vacuum was high.

[mikedjames]