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Wed Jun 05, 2019 4:00 am

I don’t know who made the fuel pump, but it says “made in Brazil” on it. It’s putting out 4.5 psi and I want to knock it down to 2.5.

Do you think I can get it down to 2.5 with (how many) gaskets, or should I go the pressure regulator route?

Wed Jun 05, 2019 4:35 am

According to the factory manual, max delivery pressure should be between 3.0 and 5.0psi. Your's seems to be in that range. Why change it?

Wed Jun 05, 2019 9:15 am

A lotta folks on here warn against going above 3 PSI.

And there are symptoms as well. Gasoline smell in the garage overnight...from under the decklid, nowhere else.

Wed Jun 05, 2019 9:26 am

Am thinking that the main diaphragm spring in the fuel pump should have a fairly linear spring rate (lbs./in.). So if you take off the fuel pump and measure the maximum stroke of the fuel pump actuating rod underneath (i.e. while slowly rotating the engine crank, and taking measurement from lowest point to highest point that rod moves), then stack gaskets to thickness about 1/2 that rod travel length, it should cut your fuel pump pressure by approximately 1/2 as well. Or whatever other ratio you want to use -- e.g. gasket stack thickness of 1/3 rod stroke length should reduce max fuel pressure by about 1/3, and etc.

All of that is "in theory" anyway -- there may some additional effects due to preload in the spring, etc. But gives you a starting point to shoot for, in any case. Then adjust gasket stack thickness up or down to get the actual measured fuel pressure reading you desire.

Wed Jun 05, 2019 9:57 am

Tinsnips wrote: A lotta folks on here warn against going above 3 PSI.

And there are symptoms as well. Gasoline smell in the garage overnight...from under the decklid, nowhere else.

I'm running 4.0 with no issues at all. It is possible that VW engineers knew what they were doing. Perhaps you have a needle valve that has dirt in it and not closing fully.

Wed Jun 05, 2019 10:59 am

Tinsnips wrote: A lotta folks on here warn against going above 3 PSI.

And there are symptoms as well. Gasoline smell in the garage overnight...from under the decklid, nowhere else.

There's no end to the nonsense posted in these forums. The pressure spec depends entirely on which carburetor you're using.
As mentioned, the spec for the 34 PICT-3 is 3-5 psi. Earlier carbs had a lower fuel pressure spec.
You can easily determine if your carb is getting overfueled by checking the level in the float bowl. That is where any effect
of overpressure begins and ends. If it's too high, you can use a thicker washer under the needle valve, replace the
needle valve, use gaskets under the fuel pump, use a different or "modified" diaphragm spring in the pump, or try a
different pump (the original Pierburg mechanical pumps typically output less psi than aftermarket ones). Each gasket
of typical thickness (.3 mm) under the pump will reduce pressure at most 2%. That means at least 10 gaskets per psi.
But using that many gaskets will reduce the stroke so much you'll likely cause fuel starvation at high speed.

Your garage fuel smell is caused by a leak somehere, not excessive fuel pressure. If you don't have the fuel cutoff valve that
VW originally put in your fuel line, it might simply be slow gravity flow of gas from the tank to the carb while it's parked. Again, simply popping
the top of the carb and checking the fuel level will reveal that.

Wed Jun 05, 2019 11:28 am

I have never used a fuel pump with more than one genuine gasket thickness either side of the fuel pump spacer. I run a genuine VW squaretop pump which lasted 30 years and 450,000 miles before a rebuild was required.

As kreemoweet points out there is the likelyhood of fuel starvation at high speed ie wide open throttle.

I bet you a lot of people are not running the appropriate washer thickness under the needle valve.

Seriously the fuel pump is a significant part of running the vehicle and people run these crappy fuel pumps to save money and wonder why they have problems with them.

Just buy a genuine pump/overhaul kit and be done with it.

Thu Jun 06, 2019 1:40 pm

Tinsnips wrote: I don’t know who made the fuel pump, but it says “made in Brazil” on it. It’s putting out 4.5 psi and I want to knock it down to 2.5.

Do you think I can get it down to 2.5 with (how many) gaskets, or should I go the pressure regulator route?

What is the motor and carb?

Thu Jun 06, 2019 1:42 pm

fuel pressure and fuel volume.

The smell is coming from somewhere else.

Thu Jun 06, 2019 3:56 pm

Anybody else note that gaskets come in a staggering array of thicknesses?

I have three different gaskets in my stash right now. The thickest is about .060" and the thinnest is about .010". That's .25mm to 1.5mm, so a larger pressure difference per thick gasket according to the numbers kreemoweet posted.

So to answer with a given number, we'd need to know what gaskets you have IF you actually do need to lower your pressure.

Robbie

Thu Jun 06, 2019 4:22 pm

asiab3 wrote: Anybody else note that gaskets come in a staggering array of thicknesses?

I have three different gaskets in my stash right now. The thickest is about .060" and the thinnest is about .010". That's .25mm to 1.5mm, so a larger pressure difference per thick gasket according to the numbers kreemoweet posted.

So to answer with a given number, we'd need to know what gaskets you have IF you actually do need to lower your pressure.

Robbie

We also need to know the stroke of the pump rod at 4.5psi before we'd know the gasket thickness required to reduce it by any amount (assuming linear spring rate) and ideally the rpm that pressure should be measure at for his engine.

Sat Jun 08, 2019 10:45 am

So here's my fuel level....

1970 beetle, 30 PICT-3.

Sat Jun 08, 2019 1:07 pm

Do you have some kind of shop manual that shows you how to measure, and what your settings should be?

The measurement is down to the millimeter, so I’m not even going to make a guess from here if you are high, low, or just right.

Robbie

Sat Jun 08, 2019 1:41 pm

I had about 7 psi, dropped to 4 psi with about for or five gaskets as I recall You I guess will need one or two to get what you desire, of course which thickness gasket?

Bug On!

Sat Jun 08, 2019 6:41 pm

While the pump gaskets do vary in thickness, so do the pump flanges. The newer ones that go with the repro pumps are a different thickness (I had posted on this elsewhere) -- don't remember now if it is thicker or thinner.

The gasket for the carb cover also varies in thickness. The newer ones are thicker and need an additional (or thicker) washer under the needle valve to maintain the correct float height.

Sat Jun 08, 2019 7:38 pm

Hmm, that carb of Tinsnips has one thick-ass gasket, and looks like one of the cover
screws has the head broken off. Leaving a carb screw off could very well result in
leakage, and fuel odors.

Sat Jun 08, 2019 7:58 pm

Quote from Tinsnips.

"I don’t know who made the fuel pump, but it says “made in Brazil” on it. It’s putting out 4.5 psi and I want to knock it down to 2.5".

What are you measuring the fuel pressure with and how accurate do you know it is?

Sun Jun 09, 2019 3:00 am

kreemoweet wrote: Hmm, that carb of Tinsnips has one thick-ass gasket, and looks like one of the cover
screws has the head broken off. Leaving a carb screw off could very well result in
leakage, and fuel odors.

That’s a stud I had to install. A PO stripped the bowl threads.

Many thanks to all for the input.

Sun Jun 09, 2019 7:04 am

If it was my VW and i was running that fuel pressure, I'd do the following-

* Remove the fuel pump and measure how much the fuel pump pushrod is sticking up at its highest travel above the fuel pump stand. It should be 13mm. There are different fuel pump plastic or bakelite stands out there. Folks should ALWAYS measure this before simply slapping the pump on.

In all likelihood, your fuel pump main diaphragm spring is too stiff. That spring is what determines the fuel pressure. Yes, you can reduce the pressure by stacking gaskets under the pump to lift it up, away from the pushrod, reducing the travel of the pump rocker. However, you're lowering the fuel pressure AND VOLUME.

Every Brazilian or German Pierburg fuel pump I've restored and checked the fuel pressure on afterward was right at or near 3psi with only one gasket under the pump. I use the OEM Effbe rebuild kits in my restored fuel pumps. I've also used NOS Effbe fuel pump rebuild kits and got 3psi each time. In all cases, the fuel pump pushrod was measured at 13mm above the fuel pump stand at its highest travel.

Tue Jun 11, 2019 1:26 pm

Tinsnips wrote:

So here's my fuel level....

1970 beetle, 30 PICT-3.

Listen horse, you're not going anywhere. Separate the two issues - the smell, the fuel pressure. Now, issue 2 the fuel pressure is solved because it is a non-issue and you can get on with issue 1- the fuel smell.

Sniff around, inspect the fittings and hose, look for discoloration, ask a friend with a big schnozz to sniff out the source of the issue.