Re: Weber fuel recirculation- Questions
 

A nice friendly system would cost about $500.. still wanna play ?

If you got the bucks, patience, and system outline it's idiot proof.

$500 ?? How'd you arrive at that figure? You mean if he pays for labor?

Hey Sherwood

My float levels are/were good, I checked them a few times during my troubleshooting. Maybe the vibrations are a factor, but that's a stretch I think. I tried every fuel pressure beteween 2 psi and 6 psi too.

More possible that the 9 inch fuchs and sticky rubber generate a whole lot more side g's than those webers were ever designed to handle. One thing is for sure - the problem completely disappeared after I plugged those holes off. Car runs like a champ at all throttle openings, and there isn't a hint of sputtering at the track or while slaloming now. Before I plugged the holes even a single hard turn would flood the carbs.

It certainly is strange that no one else has seen or heard of this problem. I wonder how many guys who have actually drilled their carbs also track their cars? I wonder too if the PO free handed the holes in the wrong place instead of using the PMO jig. That wouldn't surprise me since the short block I inhereted with these carbs had some creepy/wacky things done to it (don't ask - if you consider 911 engines to be automotive porn then this guy was into s&m). :eek:

Thanks for the interest.

good thought. good analogy.

I have a sweet 3/8" flex head Snap-On for such a routine.
Some reg mfg say one way to test their reg is to remove all spring tension, so it's not considered damaging afaik. What your psi ga reads is what you get. It's not like a torque wrench or an analog ga that reads more accurately in the middle.

personally I like to find the lowest psi, if needed, by starting a few psi higher and slowly reduce spring tension till that point is reached.. in other words the diaphram has some spring to it. I don't like the idea of zero spring on the diaphram.. actually diaphrams should be alcohol resistant, imo, which isn't always the case.

Carbs vibrating can cause various prob's . Sherwood gave an educated guess imo.

The PO sounds like a consideration 'cause I've never read or heard of such a thing.. although a pro might have? Nice that the seemingly remote answer worked out..


fwiw, it's a carb eat MFI world. http://www.pelicanparts.com/support/smileys/wat6.gif

My MS PowerPoint skills should do.

A by-pass/BP reg

http://forums.pelicanparts.com/uploa...1108713437.jpg

ps: I can't think of a reason for a check valve ?

Ron,
Only reason I can think of for a check valve is to keep some residual pressure in the lines for startup. This is not a fuel injected engine where a head of fuel pressure is necessary. There should be plenty of fuel in the bowls for startup even with empty fuel supply and return lines. In fact, even w/zero fuel pressure, one could idle the engine for a couple of minutes on the fuel in the float bowls.

I would also suggest placing the filters on the pressure side of the FP. Other than that, looks fine despite the number of fuel lines required.

Sherwood

yep.. I understand the "w/zero". I miss being able to start and run a carb'd engine from a coke bottle full of gas, lol.

The CIS filter that Grady mentioned is a good one for sure, although Racor makes a nice 150psi all steel with an internal replacable filter that can be bought with a 2 micron filter. The Racor Model 110 costs about $90. The element is about $15. I like the 2 micron filters on these 911 carbs. For more entertainment a differential psi ga could be plumbed in for filter monitoring with any filter. I'm not sure that a ga before and after the filter can be used for this.

For example my filter is maxed out dirty at 5# differential under max 30gph load. So if 20mpg = 3gph, 30gph/3gph the 10% max flow. Then 5# differential max/ 1/10 = .5# diff.. If the differential is linear?
I know friction loss isn't linear to flow. So lets say filter loading is not linear. Then the differential could be 1/2 of the above .5# = .25#. I'd have trouble reading that difference between 2 ga placed before and after the filter. Actually I think it's the square of the difference in flow, which is even a smaller differential at 3gph.

What I'm searching for is a monitoring reason to have a ga before and after the filter ?

Sherwood,

I agree about the heat soak issues. Remember my priority list.
1) Keeping the engine cool.
2) Insulating the carburetors from the heat.
3) Keeping cool fuel to the carburetors.

Keeping the engine cool is first and foremost addressed with the engine cooling fan. The 1.82:1 fan ratio is the best and most economical solution. Of course front oil coolers also contribute.

The Factory/PMO insulators between the heads and intake manifold are a must. We used them three deep 30 years ago.

I agree; a fan in the engine compartment will significantly help the heat soak issue.

I found the part number for a Fuel Injection Schrader valve to use as a fuel pressure test port or sampling port. It has an 1/8” pipe fitting and is designed for use with fuel. It has a steel safety cap and looks just like a tire valve stem. It is “Valve assembly with cap” Ford #EOA Y-9H 321-A. I’ll buy one on Monday for all to see.

There is a good reason for a check valve at the pump and an open restrictor in the return. When the fuel system heat soaks the expansion from bubbles forces the fuel and bubbles toward the return and not the supply. If the return is blocked by a sealed pressure relief valve, the pressure will force its way past the N&S or the supply pump in the absence of a check valve. Not good.


I’ll modify my original list of components:
1) Fuel tank.
2) Electric fuel pump.
3) Filter.
4) Tee on supply side.
5) Banjo fitting at carb (4 total).
6) Tee on return side with pressure/sample port.
7) Fuel pressure sender (not yet shown).
8) Bypass pressure regulator.
9) Tee for pump relief (if used).

To read:
1) Fuel tank.
2) Filter screen fitting in tank.
3) Electric fuel pump with check valve.
4) Fuel filter.
5) Supply hose & pipe (7 mm, -6 size).
6) Tee fitting on supply side.
7) Double banjo fittings at carbs (4 total).
8) Tee on return side with pressure/sample port.
9) Return hose & pipe (9 mm, -8 size or larger).
10) Fuel pressure sender.
11) Fuel pressure regulator with bypass restriction.
12) Tee for pump relief (if used).
13) Return fitting to tank.


Best,
Grady

Here is the latest version:


http://forums.pelicanparts.com/uploa...1109232462.jpg

Best,
Grady

Here is the CIS fuel filter I like to use with carburetors. Bosch # 0 450 905 016.
I'll find the Porsche number.

The adaptor at each end are half the original fitting and
half Aeroquip -6 fittings silver soldered together.
Note the original copper sealing ring.
The silver -6 caps are to keep it clean while in the spare parts box.
There is a very nice rubber mounted bracket for attaching this
to the front cross member. I’ll find the Porsche part numbers.



http://forums.pelicanparts.com/uploa...1109342256.jpg

it even has its own bracket??! cool!

Here is what Pelican joefranz has for his front mounted fuel
pump on his ’73.5T now carbureted 3.0 and light weight.
He made this slick bracket from a rear pump bracket.
He has the filter and fuel pressure regulator at the rear
(next to the CDI) but he has been following this thread
and may relocate to the front.

That is a Bosch CIS pump and the new Pierburg pump.


http://forums.pelicanparts.com/uploa...1109351138.jpg


http://forums.pelicanparts.com/uploa...1109351183.jpg

Best,
Grady

FWIW, I'm in favor of locating maintenance items (like a fuel filter) within easy access less they be forgotten and not maintained.

Sherwood

How much does the stock CIS pump weigh?

Randy,

I’ll get Pelican joefranz to reply to your question. He has all that info. There is a noticeable difference in weight – his goal.

The above Bosch filter weighs 275+/-1 grams with the (steel & silver) adapters but without the caps. I’m sure there are some Porsche racing parts that are even lighter.

Best,
Grady

Thx Grady - BTW, Richard Parr told me directly that only the two little filters he supplies need to be used. That's all I have in there now, but an extra, big filter up front can't be a bad idea.

The Bosch pump weighs 28 oz.
The pierburg pump wieghs 9 oz.
The weights were done on a postage scale pre-loaded to the middle of its range, so the weights should be reasonably accurate.

The fuel pump bracket pictured above is actually a standard porsche part.
It's listed in the PET as a rear mount for a 930.

I'm using a Racor filter, as recommended by Steve Weiner. There is a bit of a weight penalty with the Racor, I don't have the exact number at the moment, but I think it was about a pound heavier than the aluminum CIS filter. It's also a bit bulky -- would prabaly be tough to mount on the front crossmember.

I think the bracket Grady is referring to is one that I made to mount the filter and Holley in the original filter/accumulator location.

http://forums.pelicanparts.com/uploa...1109396452.jpg

I'm still a couple of months away from getting my car back together, so I don't know yet how any of what I've done is going to work.

Joe

http://forums.pelicanparts.com/uploa...1302798517.jpg

Latest version.

1) Fuel tank.
2) Filter screen fitting in tank.
3) Electric fuel pump with check valve.
4) Fuel filter.
5) Supply hose & pipe (7 mm, -6 size).
6) Tee fitting on supply side.
7) Double banjo fittings at carbs (4 total).
8) Tee on return side with pressure/sample port.
9) Return hose & pipe (9 mm, -8 size or larger).
10) Fuel pressure sender.
11) Fuel pressure regulator with bypass restriction.
12) Tee for pump relief (if used).
13) Return fitting to tank.

Best,
Grady

I may need to do this to. Great Thread. I just read the first few posts but look forward to reading this later this evening. ...great knowledge on this board!
Thanks!