Hello all!

Having some on going difficulties with my fuel system. Last time at the track I had a lean running condition when under load on the 1-2 bank. Swapped a gasket once back home and now can't replicate the problem.

Decided I was going to refresh a few components as a precautionary measure. Fuel regulator (as this is where the split happens between the left and right carbs), fuel pressure gauge (the old one was well old), and adding a spare carb to my track side spares.

Previously I had not had a problem with fuel pressure per the gauge. After swapping in a fresh Holley 12-804 and an oil filled gauge I was unable to regulate the pressure down to 3 psi. Was not able to regulated it lower than 15 psi for that matter.

A little research on the web indicated that the 12-804 and the higher pressure 12-803 sometimes get mislabeled. So I bought a rebuild kit which came with both springs. Swapped the new low pressure spring into the new regulator. Initially I could get the pressure in the 3 lb range but after a sort while the pressure would creep up. To make matters worse if I bounce the throttle I actually can watch the fuel pressure drop off

The fuel pump is a Holley blue top so it has a max pressure of 14 psi.

My next track day is 2 Saturdays from now so I need to sort this soon. Has anyone else run across this before?

Thanks,

Miguel

Miguel,
The simpler (and probably simpler) way to go about this would be to just put a self-regulated Carter-style pump in. The ones CB Performance sells are well known for their reliability and match well with just about any dual carb setup.

http://www.cbperformance.com/ProductDetail...roductCode=3193

If nothing else, you could order one as your spare and if you have trouble at the track day, this would be simple to install at the track.

I went with a full (nearly) AN fitting and hose full supply system a while back. I guess I could remove the ends at the pump and install one of those but it seems like the Holley pump and reg is a pretty common solution. No reason it shouldn't work for me as well as it works for everyone else....

I've never tried the carter rotary pump, because of the lack of screw type fittings

I've been through 2 facets, 3 holley's, and 1 of the larger carter pumps for v8's that is not an inline style on my race car

I've really struggled with all of the holley's. my builder told me how reliable and good they were, but after 2 failed I ended up putting a facet back in place of that pump. I still run one holey as my primary pump but really don't trust it either.

(I run a 2 pump fuel system)

I wonder if your holley could be part of the problem?
mine would run correct pressure in the pits and for 2 laps or so, but then I'd come in when the car started acting up and would have a loss of pressure until it cooled

I know yours is creeping up, but the fact that its not consistent is also a concern.

I think the Holley Blue puts out too much volume for your regulator to compensate.
You either need a smaller pump or a second regulator with bypass,
like Paul (eimc) describes in his fuel issue thread.

Too big of a pump for the regulator. They can only regulate what ranges they were designed for. Either order another low-pressure Holley (2-5 psi) or try what Chris recommends.

Right-O swapping out the fuel pump

So one C-Note for for a Holley Red or 2 for the Mallory

Pour money and stir!

M

Or as Chris suggested, set up a bypass style fuel system layout to dump the excess volume back to the tank. If you do that, the extra volume won't be a problem and pressure regulation won't be an issue either.

I was trying to keep it simple for the initial fuel system so I opted for a return-less set up. I have a similar setup on my GTV, but am using a facet pump and redline regulator/filter unit for the components, and it has not given me problems in the last three years.

I have seen a fuel return setup on DCOE's that was simple and clean in theory. A fuel outlet is added to the bowls which lets the bowls over flow back to the fuel tank. The floats are removed and the pick up for this outlet is set at the ideal fuel level line. The bowls always are full and the pressure in the system is minimized. I have the impression that this style of system was outlawed sometime ago....

Either way not trying to reinvent things here. Looking for the simplest system to get me on the track enjoying the ride.

M

Just this last weekend (first time on the track) I was having a similar issue.
Car would run great for ~10 minutes hard, then start to bog at WOT and not have the same pep.
Hard to tell if it is a lean or rich condition (murphy's law = datalogging was not working when this happened for AFR & EGTs).

I suspect a fuel pressure problem.
I have the holley red pump & regulator up front with the fuel cell, 3/8" steel line through the tunnel and a pressure gauge at the splitter in the back where they split and go to dual fuel filters & 40 IDFs.

I have nice new lines everywhere except from the fuel filters to the carbs.
Damn those weber fuel inlets being 5/16" / 8-9mm!
I will definitely be replacing the weber inlet hosebarbs with AN fittings...( anyone know the drill & tap size for that?)

I am even considering putting in a fuel pressure sensor and logging it with everything else.
It is not heat soak as I have the phenolic spacers, tall intakes, and carbs are cool to the touch when I come in.

There is a fitting that threads into the weber with a crush washer and a -6AN on the other side. Took me a while to figure out the thread but it exists. I'll look in my file tomorrow and find the part number. Super nice to have when you have to pull carbs and mess with the intake system.

M

In the past I've tapped them with 1/8" npt IIRC.
More recently I found some fittings with the correct metric thread.
I think they're M10 x 1 or something odd like that and I think I got them at Pegasus.

One random thought after reading the thread again. Are you sure you're measuring pressure in the right place? If you measure upstream of the regulator, you will certainly see higher pressure ...

The gauge is between the reg and the carb to measure the pressure in the supply to the carb

Here is the part number form Summit RUS-670480 and a link: -6AN to 10x1

Makes for a super clean install and very serviceable.

Miguel

Thanks both of you.

I looked at the carbs last night without pulling the lines.
It looks like the hose barb nipples on the carbs is just pressfit in.
Is that correct, or is it actually threaded?

I'll order the parts from the link above and I have the taps, but I just wanted to be prepared to do it right.
(And sorry for the thread-hijack)

Some Webers have pressed in hose nipples.
Others have the threads on both sides with a plug in the unused side.
I would use npt to AN adapters to replace the pressed in nipples. The fittings are only a couple bucks each.

No problem on the thread jacking.

Mallory pump came in yesterday. Swapped it in last night. Pressure spot on. Thanks Chris and everyone who helped!

M

which mallory pump (part number) did you end up using?

I am still looking for a holley alternative myself

Mallory Pump

Chris mentioned he uses the Mallory on his car, which for me is a pretty strong endorsement. And your reporting of going through the Holley's was another valuable data point.

Once I received it I was very impressed with the build quality. It might be a smidgen heavier though.

If you are going to mount it where the Holley was before you will have to rotate the body around on the bracket so the inlet and outlet match. At first it does not seem like it will rotate but it does. Slow and steady pressure will get it started.

Before I opened this thread, my search here on the forum turned up as many (subjectively) threads of people using the blue tops on carbs as red tops.... For future searchers don't go for the blue top if you are shopping for a pump.