Gradual fuel pressure decrease.... Why?
 

Hi all,

After 5 years parked and an engine transplant, the car starts and runs great, 3psi on the regulator to start, after about 5-10 minutes (or less) running fuel pressure gradually drops (over several minutes) to nearly zero.

Running 44 idfs. Fuel system comprises tank>filter>pump>regulator/gauge>carbs.

I replaced the filter and the pump and there was no change.

Are symptoms consistent with a bad regulator? Could storage have gummed it up or caused it to malfunciton?

Thanks, Dave

after 5 years parked, I'd be tearing the carbs apart and soaking them in solvent.

But yeah, sounds like you have a bad regulator. What kind is it?

Thanks Jared - engine is a brand new FAT build, new 44 IDFs. I can't recall the make of the regulator. I may crack it wide open and flush it, maybe it is partially blocked?

Do regulators simply restrict/constrict the fuel flow?

THanks.

You need to figure out what regulator you have. Get a picture.

Yes, a regulator works off the idea of constriction, think thumb on the end of a garden hose.

We arent talking a lot of pressure here with carbs... 5psi at the most.

What fuel pump are you running and WHERE is it located?

What kind of gauge are you using as well? Is it calibrated?

http://photos.at-speed.com/Cars/1968...p4Wuq&lb=1&s=A

Holley fuel pressure regulator Summit fuel pressure gauge - at-speed photos

Holley regulator and gauge, not calibrated, basically identical to the setup pictured. Both sat while car was stored.

Have run two different pumps to cross check. First a US made pump, looks like a small bosch, worked fine with prev. engine, sat while car was stored, I susepct it was still OK. Second just installed, a brand new carter. I suspect I wasted some cash on this.

Pump and filter are installed in front trunk, beside spare, big (new) fuel filter first, then pump. Regulator is in engine bay, below battery tray.

Dat's it.....

Since this is a double post, see my answer in the other one.

Based on your thumb on hose description, I bet there is something blocking the regulator once the fuel starts to flow.... I had suspected this and blew out the the line backwards, but may not have cleared whatever is blocking. Thoughts?

If there's no blockage, John's probably right.

Just disconnected the carbs, backed off the regulator, ran the fuel pump, dumping the gas into a glass jar. Some bits of black rubber like stuff in the first half gallon, clean after that. reconnected, went to adjust the regulator and it would not reduce the fuel pressure which sat 9psi. I see that regulator has a rebeuld kit which includes a rubber diaphragm..... hmmmm

That is the same regulator I used on the race car and I had to rebuild it every 3 years or so. The guys that ran "street" gas had to rebuild it every 18 months or so as the chemicals in the gas will eat the neopreme right up. Worse if the car does nor run often enough to fully flush out the fuel system. I used to use Marvel Mystery Oil in the gas, even race 100 octane as it was not as good in 2010 as it was in 2000. You can always open it up to see what the internals look like?

You did not mention the tin or seals and if the regulator is under the battery tray then that area can get really hot.

Tin is fresh and intact and seals are in place. One hole on drivers' side where ductwork went, will seal that, 914/6 oil tank holes, will leave those.

The problem occurs even though the engine and bay do not get exceptionally hot (yet). The weather here is cool. I have not put the cooling system to much of a test yet, but all is in good order, including the thermostat bellows which works as it should.

This is adding up fast, thanks. I will be picking up a rebuild kit tomorrow, and will install a clear fuel filter in the engine bay, as much to monitor the condition of the regulator as anything else.

Thanks for the guidance.

Are you aware of a more long-lived regulator?

Are there insulators between the carbs and the manifolds?

Thick gaskets anyway - 1/8" or so. Does that count? Tall manifolds too.

No, see my post in the other one you made.

OK, thanks guys. I will deal with the supply issues first and test. I'm certain that the problem described occurs with cool carbs and engine bay. Once that's fixed we'll see what happens when things heat up a bit more.
Thanks very much for the guidance.

Dave

Update:
Upon disassembly, regulator does not APPEAR to have a problem, however it is possible that there may still be some crud in the lines below.

Am contemplating options, there are some things I should change about this setup while I'm at it. Like the need for a fuel pump that requires a regualtor at all, or installing anything that may require maintenance below the battery tray or having multiple inaccessible hose clamps buried inaccessibly under the car, or.....

I suggest you look for Bob Tomlinson's Original Weber Tech Manual or Pelican Parts.com - Haynes Carburetor Manual this right here.

You need to do a bit of reading before going any further. Thick gaskets are not the same as carb insulators. I suggest you read up on the basics, then come up with an idea for a fuel system based off of that.

FAT Performance should have also given you an idea of how to set up the carbs for this engine.

I've been thinking about this problem some more.. What kind of cam and headwork does your engine have?

44's may be too much for your engine.

Engine is a turnkey FAT motor, dyno tuned and run in with 44IDFs in place at their facility. Idles beautifully, runs great, very strong, until fuel pressure drops. Heads were totally rebuilt and have larger than stock intake and exhuast valves (can't recall the size) and were ported, manifolds matched etc.....

BTW, FAT has been great to deal with, nice people, very helpful.

I expect the issue is simpler and more basic than carb size, (I would hope so!) at least I will be certain to eliminate the possibility fuel supply problems before going further. This setup worked fine with the previous engine but sat for several years.

Have not had a chance to run again with revised fuel system, but will hopefully tinker this weeekend. I have a 3.5 psi vane type pump, will run without a regulator but will rig the gauge and watch what happens.

Have some experience with webers - last engine had 42DCNFs, I rebuilt a set from a maserati merak, jetted, synched, setup myself, am well acquainted with the basics, though I am hardly an expert.

Will re-read the weber books I have for "first principles" on fuel supply, (just in case) but the question was asked hoping to get some opinions from those (like John Rogers) who have thoughtfully built and learned from track cars, without budget as the first priority.

Thanks as always, going to dig out the weber books.

Dave

Well after several ideas such as spacer blocks and such, my only other suggestion is to find a dyno shop and get someone that knows Webers and hopefully Porsches with carbs and run the car on the dyno. In southern CA we are very fortunate to have several and ALL the race pre shops use them and as Wayne Baker (#22 car) likes to say: an hour on the dyno is worth a DAY tinkering at the track!

As part of the setup they hook up fuel pressure, ignition sensors and even exhaust temps from each cylinder so everything can be seen and adjustments made. That is what was done on my car every time we had the engine out or at the beginning of every race season.

The issue with fuel is NOT pressure but flow ( gallons per minute) and it is measured by how well the engine handles high power runs and doing this over a 30 minute or 1 hour race session. There are several web sites that let you enter all your engine specs and it gives you what capacity pump is required. This is usually for water cooled engines though and we found that getting a pump with 150% or their recommendation worked very well. I used Holly pumps and the capacity ended up giving a fuel pressure of 6# and the regulator lowered it to 3.5 or so. Note the regulator reduces pressure and should NOT reduce flow and I think the Holley regulator does this well? When the race car was built, the complete stock fuel system was pulled and trashed. We did not use a bottom feed tank, as the fuel cell suction came out the top with a baffle for the pickup. We used 1/2 inch SS solid lines, no return, no filter at pump suction, Porsche 930 filter at the engine compt just before the lines split for each carb, each carb had a small filter, the fuel inlets at each carb was connected to smooth out pulses and surges and that is where the pressure gauge was (not on the filter). We tested capacity yearly as part of the dyno test and if I remember correctly it was about 25 GPH or so. The carbs were rebuilt each year and every two years sent to Pierce Manifolds for a complete redo which is $$$$$$ but they are better than new.

have you ever cleaned or replaced the metal mesh sock/strainer/filter that is on the fuel outlet tube inside the fuel tank? did you remove and flush the tank prior to installing your new engine? have you replaced EVERY inch of fuel line?

"black crud"...deteriorated fuel line? btw, if you are using the the CB/Carter version pump, when you received it there may have been a round metal canister attached. it is a before the pump filter. when i installed the CB pump on my carbed car i took the metal filter off and replaced it with a stock FI filter upstream of the pump.

on p 50 of the cb weber manual. note item #3. a gause filter that is in the fuel inlet housing that is located on what would be the outside of the carbs when installed (1 per each carb). with what appears to be your fuel delivery issues, i would ensure they are clear as well.