SAAC Forum

In some circles, Holley power valves have developed the reputation for being fragile.

What happens is that in the case of a backfire, the carbs vacuum chamber is instantly positively (+) pressurize and works the diaphram in reverse to what it is supposed to do.

This could be a common abnormality caused by the choke being too lean in cold temps. Cars that don't get used often in winter driving may never have had the choke adjusted right and having a manual choke can be a little bit of a challenge in sub zero temps too.

This can over stress the diaphragm and cause an "air" leak. Once ruptured or cracked, when the engine is running normally, fuel will leak through the diaphram and into the intake manifold.
How much it leaks fuel depends on how bad the leak is.

Normally there will be symptoms of this that illuminate themselves in the engine running very rich at idle suddenly. If you do not have those symptoms, it is very unlikely that the power valve is defective, so leave it alone.


I think that the change in dependability of the power valves is likely the change in the contractors or suppliers that build them for Holley. It isn't something that anyone talked about having issues with in the '60s that I recall and Holley didn't start to install anti-backfire valves in their carbs until somewhere in the late '70s.

One could argue that addition is in essence a default acknowledgement of an issue that needed to be addressed I think rather convincingly.


That Moroso tool is something that is very usefull to someone who disassembles and reassembles Holley carbs more then once in a while since they would want to be 100% certain there were no component issues.

It doesn't exist to create paranoia.


Personally I just ran into a bad cycle of something like a 50% "bad out of the package" situation and for my own peace of mind wanted reassurance that the new valves were ok. So I bought it.

Used in conjunction with a vacuum pump it lets you verify the opening point of the power valve as well.

For me it is a valuable tool.

Again, I'm not arguing. We each have had out own experiences. Some possibly are just unique.

I have been running unleaded with 10% ethanol for about 49 years and have never had any of these corrosion issues that some are describing.

As GT350Shelb I think correctly points out, the initial quality of the part exposed to the ethanol is a factor.

Corrosion caused by higher levels of ethanol in the gas has been documented, no question but I just don't see it at the 10% level. I actually do not know if the actual formula for the fuel is varying according to the location and thus the refinery that makes it but that is just a remote thought that is only a remote possibility?

I'm sorry for your troubles and hope that you can find a solution that is workable for you.

First off, I am not arguing, just saying what I have experienced personally.

I bought my '68 GT350 on April 4, 1972.

Unleaded ethanol has been around since about 1975 which I have always used.
The only advantage that I found to using SUNOCO Racing gas, if it is an advantage, is that the car will immediately idle down from 800 something to 700 something.

I do not like the white lead deposits it leaves on the plugs and the valves or on the observable portions of the exhaust system.


My experiences with the original gas tanks is that they need to be kept as full as you can get them for storage, not the opposite.



Most of my 68 GT350 has used "Aeroquip hose" since around that time and 304 ss hard tubing where applicable so that might be a factor in the results with those components?

About the only original fuel hose that I can think of that is still on the car right now is from the fuel pick up to the metal fuel line outside of the tank. It is still original. Has been off of the car and examined and still un-cracked or showing signs of interior deterioration.

What you have experienced and that you share with others is appreciated and I note it. I can't deny your experience.



The carb valves show no evidence of foreign materials on them. They just show a mark where the rubber meets the metal ring of the seat.

I have also had issues with failed power valves but that isn't a recent thing. It is an on going phenomena. That goes way back to my start... and yes I do use the check valves installed in the throttle plates even when not original to the carbs.

I invested in a Moroso "power valve" check tool and my initial experiment of 12 brand new, "still in the bubble wrapper packaging" showed 50%, yes half, had vacuum leaks brand new, so really what needs to be factored into that equation is the quality level of the original part or the lack of quality in the original SERVICE  parts?


One probably does need to take into account my location though. There are places on the Earth where the compass does not work. In one case it is called the South Seas Anomaly. Who is to say there isn't another location where the normal laws of physics do not apply and right here in the NYC area could be one of them? After all,  to some, I defy ANY sensible logic? 



On other vehicles here, everyday use cars, many of the "rubber" fuel lines have been replaced. There are no "factory original part numbers" on them and are largely NAPA parts. So far, so good...knock on wood, but simply put, I have not experienced any of the side effects others are describing in over 49 years, so color me cautious but respectful of others more experienced then I am.

With these "bumps of knowledge" on my head and if one is truly wiser by making mistakes and learning from them, I should be, but am not, in the "genius" class by now and still the general consensus is that I am just the "Village Idiot" and we just "humor Doug"?  That's actually ok with me since I long ago learned to accept that and at least get invited to the barque afterwards.. .even though?

After all, I am 75 now and don't look my age. I only look 74 so it confuses people because I still use words that are no longer in the vernacular, but I still remember them AND so far only one person has threatened me with a gun and he was just a medical doctor so that is likely understandable anyway by his own piers?

We have been running on unleaded 92 octane with 10% ethanol in New York State since about 1975.

There are few issues with it. Not many.

1) The advertised compression ratios shown by Ford mean little. In virtually all instances the actual measure static compression ratio is just about .5 point less.

That puts engines like the 289 at about 9.6:1 or so. Engines with actual static compression ratios in that range with non-domed pistons run fine on 92 unleaded. You just need to stay under 10:1 actual. That is the limit of the compressibility of 92.

During the first "gas shortage" here, "we" found that the 306hp Shelby version would run ok on "regular" which was posted at 89 octane.


Engines that were having issues even on 92 were engines with domed pistons like the Boss 302, Boss 351, 427 MR, and Boss 429.

2) Ethanol reacting negatively with the "rubber" components in the fuel system is largely over rated. Original Ford hoses and components in the system have/had no issues with it AT ALL. Aftermarket hose in the auto stores, that could be another story AT THE TIME but these days aftermarket hose marked "FUEL" is made to use with ethanol.
Fuel Pump diaphrams do not have any issues with 10% ethanol. You won't have issues with ethanol until you get to around a 25% level and there isn't anywhere in North America where companies sell that in the pump.

3) The ONLY issue that I have experienced with unleaded Ethanol fuel in the last 49 years is that the Holley carb VITON inlet valves tend to stick CLOSED after the engine has been sitting dormant for around 30 days.
The carbs like it better if you set the floats a little lower then Holley instructs. This isn't usually an issue on the primary bowls but the secondaries are a little bit of a PITA because by design there is less float travel in the secondaries.
Those admittedly I do struggle with to get just right.


There are those who feel that the engines run better on the equivalent of 106 leaded racing gas or even 103 leaded but that fuel contains so much lead that it introduces other negatives to the fuel system and even the exhaust system.

You can argue that it is what the engines were designed to run on but the reality is that the current blend of 92 with ethanol supports all of them.

Each of us will obviously take our own road but my view is that if you intend to drive the car at all besides just around the block, you need to make the adjustments to what you can buy in any "gas station" out on the open road and it isn't a difficult adjustment and paranoia is not your friend in any respect.

I got over this issue 49 years ago. If I can. Anyone can.

The paranoia is a demon that you are fighting unnecessarily and it is largely imaginary.

I would not do that to a regular production Mustang let alone one identifiable as a Shelby.

In my view reactions actually cut both ways though. There are those that are openly indignant of how the car currently appears and don't have issues with expressing that and the owners are indignant that the car does not fit into the "Shelby's society's" definition of how the car should be.

Often I notice quite a visible attitude of arrogance on both sides. I personally attempt to avoid both groups and try to appreciate both even though at times it can be quite an abstract endeavor.

I suppose I should point out that I have in fact been told to "go back to my arrogant SAAC buddies" as well as politically be told by both the extreme left and right that, "we don't need you here. Stop telling people that you know "me"." So I kind of get it all, generally, if not specifically speaking.

It is very helpful if you have a thick enough skin to be able to tolerate it all and being a native New Yorker I understand that nobody here agrees on anything anyway, no one likes each other and that everyone complains about everything all the time.

All things considered though it would be nice that once in a while one of our major league sports teams could win something and at least get into the finals? See. Complaints, complaints! 

I thought it was just some kind of a tatoo on his butt? Now I understand.

Quote from: shelbymann1970 on March 08, 2024, 02:56:38 PM

Quote from: Kent on March 08, 2024, 03:04:03 AM
Yes that's a usual thing I see often and it don't make sense to mount fiberglass like this.

I always did it the right way and thought its wrong and was not done like this by the factory but I thought its better for the fiberglass and years later I found a concours restored one at a saac meet and found out my thinking and doing was right as they mounted it the same way like I did all the years.

By the way I need one of these top panels does someone here has one for sale?

what boggles my mind is the header brackets have a threaded extruded hole for the bolt so why would anyone mount it wrong because you would need a nut or clip on the backside to hold it in place and possibly tightening up on the extruded hole.

It's a no brainer to me. Very juvenile.

Mine is original Ford Service part and does not have a part number on it.

I am obviously missing something here? A fence?

Quote from: Bob Gaines on February 29, 2024, 08:11:35 PM
Shelby Parts and Restoration used to sell stainless steel ten spoke /69 Shelby lugnuts . It was found out that you had to continuously re torque them as they frequently worked loose. Not the case with the chromed steel lugnuts.

A switch from carbon steel to stainless steel in a structural application, such as lug nuts, is going to have risks.

I don't know of any application where stainless steel is used for other then a cosmetic application. It is never used for a structural application.

Where it gets threaded together, it has problems with the structural integrity of the cut threads themselves.

The chromed steel lug nuts need anti-seize compound as well.

I actually think that 100lbs-ft of torque on stainless steel is over stressing the threads.

It is a VERY good idea to use anti-seize compound on the studs and lugs. Just don't over do it.

Once re-torqued the lugs will stay where you set them.

If you don't ant-seize the studs, just washing the car and letting the lugs sit for a year or so will tend to stress out the lugs in breaking them loose. They are not hardened steel and it is easy to deform them otherwise.

In addition, it wasn't mentioned, BUT ANYWHERE you use stainless steel bolts or nuts, you virtually have to use anti-seize on them. Those things just chafe the threads for no reason and strip out easily if you don't.

I agree with Tim on the diaphram thing. They work fine and have less effort but you will never get the clutch pedal to be at the correct height. It is always too low.

The other thing is that the Centerforce in particular will push the pedal up when you are over about 5,000 rpms and I'm used to it but it always catches me by surprise and distracts me from the job at hand, which is paying attention that you don't wreck the car and kill somebody while you are at it.

The stock long three finger is what everything in the clutch pedal system is designed to operate. The diaphram is good but definitely an alien device to a vintage Mustang.


IF for some inexplicable reason that you let someone else drive the car with the diaphram in it, they are going to ask you "what's wrong with your clutch?"

Quote from: Lincoln tech on February 20, 2024, 03:08:31 PM

Quote from: deathsled on February 20, 2024, 02:21:15 PM
Hey, what happened to my post count?

Your'e a Victim Of Circumstance     

I think his days are numbered?

I think 544 actually got the medium riser with the aluminum heads that Ford called the GT40 engine. Aluminum water pump. Aluminum hub on the balancer. Magnesium intake.

Limited to 10.5:1 and 425hp in order to survive the 24hrs of Lemans.

Originally Ford referred to the cam as a "special grind" but I never saw the specs on that one but it looked like the standard solid lifter MR grind to me? Others may know more about that one.

As far as I know, you had to be someone special to get one from Ford. You just couldn't buy one from the Ford Service Department at your local dealer.