I have a power valve tester made by Moroso that works good in conjunction with a hand held vacuum pump.  I typically use it to check the vacuum rating but it also checks for leaking diaphragms.

Lorena, Texas (South of Waco)

I did find some sediment this time.  It starts out somewhat coarse and disintegrates as I rub it between my fingers until it can't be felt.  I see it in the float bowl and on the float bowl side of the metering block.  I don't see evidence of it on the other side of the metering block or the main body.
Is this contamination due to inadequate filtration?

I also got the power valve tester and the valve is a 7.5 that is fully closed at about 6psi according to the gauge on my vacuum pump and moves smoothly between 0psi and 6psi.  I don't know how accurate the gauge is.  It does hold vacuum.  The portion of the diaphragm that can be seen looks wet.  The pintle and seat look ok.  There was also fuel in the power valve cavity of the main body.  The power valve gasket was moist with fuel but the valve was tight.  Given that part of the gasket is exposed to the fuel, I don't know if that necessarily means anything.  The power valve cavity and corresponding area of the metering block have black residue consistent with what I have seen when fuel has been seeping or leaking for a while.

Can a power valve test good but still be bad somehow?
I'm thinking that the actual cause is either the metering block gasket or power valve or power valve gasket.  I'll clean it up the best I can and if it seems like a full rebuild is in order afterwards, then I'll have a good excuse to try the new 670 that I have.











Lawrenceville, GA

All good questions.  Looks like you need a finer screened fuel filter.  My experience with power valves has been if the power valve holds a vacuum, then the gasket is the problem.  Those gaskets can be touchy in remaining centered on the power valve when tightening them to the metering block; if not centered then fuel is allowed to seep into the power valve cavity in the main body.  When in doubt, just replace the power valve.

Lorena, Texas (South of Waco)

The photos of the brown stuff and your description of it sounds a lot like Phase Separation. Where enough water gets into the fuel and causes it to separate into little bits that are soft. Eventually bacteria can get in there. Also the water will rust metal. At this stage of separation : with fuels that have Ethanol in it it will harm the engine when running, with Conventional fuel it does not harm the engine when running. Either way the engine will misfire.

https://www.epa.gov/sites/production/files/2015-09/documents/waterphs.pdf


1936 Ford 3W Coupe : 56 T-Bird 312, 47 Packard 3 speed, 40 juice brakes.
1968 Merc Cyclone FB GT 390, Getting a better front clip!
1977 Ford F-250 Supercab RWD Explorer Long box.
1976 Chev Camaro RS LT
Future rebuild : 1949 Ford F-1

I don't think that is the problem given that the symptoms point to too much fuel, causing flooding.  It will be easy enough to test with a remote fuel source and fresh gas, though.  We'll see how it does after I clean it up and put it back together with new gaskets and power valve.


Lawrenceville, GA

One other thing to add. The power valve is open to manifold vacuum. When the engine is shut off warm, fuel vaporizes and then will condense in the cavity behind the power valve. If the power valve checks good and the gasket is OK then that is likely where the moisture and discoloration is from.

Although it doesn't sound like this is your problem.
There is a "fix" for leaking holley power valves that are caused by backfires. Holley makes a kit.
https://www.holley.com/products/tools/carburetor_tools/parts/125-500

A little trivia.
Back in the 80's with Fords variable venturi carburetor this vaporization issue cause the rubber diaphragm to deteriorate and since vacuum and the diaphragm was what controlled the ventura there was no throttle. The Ford fix was to drill a drain behind the diaphragm. I had a lot of customers request that I convert the Variable Venturi  to a holley 2bbl back in the day..

Dave

The Street Avenger comes with the check ball.

I cleaned everything, installed anew power valve and new gaskets.  Started it up and it was idling great.  I turned the idle screws in and it stalled - seems good.  Decided to take it for a test drive and right as I got to the bottom of my driveway, it stalled and no longer idles, again.  I got up the driveway fine.  I had to rev it to get into the primaries but doing so resulted in plenty of power to get up the driveway with ease.

Fuel pressure good, float level good, still the old needle and seat.

It is easy to start when it stalls now.  That actually seemed to change when I replaced the fuel pump.

I tested the new 7.5 power valve and I could not get it to hold vacuum.  I tested another new 6.5 power valve, and again, it would not hold vacuum.  A very slow bleed in each case.  I tested 3 used power valves, including the initial 7.5 and they all hold vacuum.  I installed the new 7.5, thinking that maybe I was somehow messing up the testing of the new valves although I don't know how I could do that - it's pretty simple.  I guess I'll try a used one and see if that takes care of it.  It was idling fine for about 5 minutes.  If the new valve is bad maybe that would be just about enough time to fill the cavity and reach the vacuum passage.

The fact that it seems to do fine with enough throttle that it should be mostly or entirely  on the primaries indicates to me that it is not a fuel quality or ignition problem  Those would just get worse in a situation where it is under load, right?.

And I just realized that I forgot to replace the vacuum cap on the ported vacuum port.  So I need to do that but that should have nothing to do with it.

What a tease, idling great for a moment and then back to the problems.


Lawrenceville, GA

If there is a very slight bleed of fuel from, say, the power valve into the main body cavity, more throttle means more air and may utilize this bit of extra fuel bleed and run ok at any throttle setting other than idle.   The pics supplied look very similar to what stale fuel will cause.  The phase separation mentioned by Robs36Ford in a previous post is what it looks like to me at this point.  The gritty brown slime and the overall brown color on everything "wet side" suggests this. About 4 years ago, someone brought in a Motorcraft 4350 that looked very similar to your Holley with the pump plunger totally destroyed and air bleeds with this gunk in them. It was so amazing that I took a few pics of this and will later look for them.  I'm sure your vehicle takes on assumed to be fresh fuel on a routine basis so stale fuel shouldn't be a factor .I also beginning to question what these swings in chemistry are doing to the specific gravity?  However, this brown debris and all that was a result of the fuel in question.  Also, stale fuel produces it's own (nasty) odor along with irritating the sinuses and eyes but that wasn't mentioned.  Very interesting unsolved mystery................my thoughts, JEFF..........


64F100 57FAIRLANE500

I know what bad gas smells like. This still smells and looks fresh.  This particular fuel is about 2 months old because I've been doing other stuff on the truck.  But generally I drive it regularly and it does not sit more than 2 weeks, so fuel is always fresh and it was fresh when I initially started noticing the intermittent problem.  Stale old fuel just isn't the reason for this to have started.  I've had it sit this long several times in the past while I did other work with absolutely no problem.  The inside of the float bowl does not look out of the ordinary for a 10 year old fuel component compared to others I've seen.  I suppose it's possible I've seen only exclusively bad things but I doubt it

I also don't think phase separation is the problem.  I have a fuel cell with a sump. If that was going on, I'd be getting the separated alcohol and water first and it simply wouldn't run or smell like gas.if that was happening.  It  certainly would not have started out idling well yesterday.  Simply bad gas also isn't likely because the first 3/5 of this tank was fine.  I use premium fuel which is typically about 5% ethanol near me so separation is possible with that but it would not be nearly as bad as it is with the lower grades.  And again, when it initially happened the fuel was fresh.

I will test it with fresh gas shortly if nothing else seems to take care of it but I'm just not convinced that it is a fuel quality problem.


Lawrenceville, GA

Hmmmm, thanks for posting. Well, not noticing the foul odor means a lot. It sure looks like something dissolved in a batch of fuel.  Is this the unibody pickup? Are you perhaps using the in-cab tank? I ask this as with my 64, it's easy to shine a good LED flash light into the filler opening and have a peek at the interior of the tank. Would be curious to know if any of this is evident there? Or could something have broken down/dissolved in the old fuel pump that was "stuck" at 12psi?? Same applies to the regulator that may have a neoprene parts??


64F100 57FAIRLANE500