[Tom Vaught]

The only time I ever saw issues with the slotted gasket on the Tri-Powers was when the vehicles were parked in the desert, you had a nasty sand/dirt storm come up, and cover the vehicle with dust. The dust would go everywhere. Guys would rubber band a rag over the breathers in the valve covers to keep the grit out of the engines.

Because the grit is everywhere in the air some of the grit can go thru the slots in the base gaskets and rest on the throttle plates. Most times the design of the Rochester Throttle blades did a nice job of sealing to the carb bores. But you need to clean that crap out of the carbs before you restart the engine. Most times the fix was take the carb apart, soak it it gasoline, and put it back together. Only had to do this a couple of times when I lived in the South West.

So the Solid/Non Slotted gaskets would allow you to proceed down the road after a nasty dust storm vs being trapped in the desert cleaning and fixing your carbs.

Some would throw a blanket over the engine to try to seal it from the dust but that rarely actually worked.

But the desert is not a city but you would be surprised at the amount of dust that collects from the normal traffic that goes into the air.
Sealing up the engine in the city was more than just an emissions deal, in my opinion.

Just my observations, but may have nothing to do with the actual story, But the Engineers did make the change for a reason.

Tom V.

[carbking]

Tom - I actually asked one of the Rochester engineers about the slots, not a vacuum leak but about unfiltered air entering the carburetor through the slots. His comments had to do with when the engine was running, not parked in a desert dust storm; but he said that virtually no air would enter the carburetor through the slots. He commented that the edge of the throttle body was a "dead" area, and that any variance in pressure in/out would be positive, that is that air would move from inside the carburetor out through the slots. Having never lived in the desert, I did not think to ask him that question.

Your comments sound reasonable; but we don't know that the engineers were actually responsible for the change. As you know, engineers don't always have the last say in what is marketed

Wish I had access to some of the internal Rochester files concerning these decisions like I do the Carter and Stromberg. Two of the most interesting reads I have ever read concerning carburetion are (1) the Stromberg file on how, if economically feasible, carburetor modifications could be made to avoid patent royalties, and (2) the Stromberg file on carburetor inventions submitted to Stromberg.

[Kenth]

Odd though that only 1959-66 Pontiac Tripowers got the closed throttle body gasket?

My understanding is that it would be beneficial to use the vented gasket with the use of
todays gas?

Looks like factory correct would be the 7015106 vented gasket after all?
This Bulletin 9C-640 is dated December 1965.

[carbking]

Kenth - there is a bulletin dated 1967.

Jon.

[Kenth]

Jon - yes those bulletins were annual, only NO Rochester Tripowers from factory 1967 and later.
Why would the problem with desert sand only apply with Pontiac Tripowers?

[Dick Boneske]

I have several NOS Tripower carbs from '59, '63, and '64. All of them have the vented gaskets. That's true of the end carbs and the center carb.

There should be no doubt in your mind, based on the bulletin above and my experience with NOS carbs, that the vented gaskets are the way to go when rebuilding Tripowers. All the kits' I've seen have both vented and non-vented gaskets.

[carbking]

In post 19, I speculated why Delco Rochester made the change from the vented to the non-vented gaskets on the end carbs.

THIS THREAD IS A GREAT EXAMPLE OF WHY I CAME TO THAT SPECULATION!!!

Kenth started it, asking what gasket he would get in one of our kits, and why. And the answer was the non-vented gasket BECAUSE that is the latest specification I have from Delco Rochester.

Tom V. made the comment about the dust storm.

Dick B. believes the vented gasket is the one to use because it was used originally (and it was, all of the bulletins printed during the actual production run of the tripowers substantiate Dick's claim of originality).

So just in this thread, we have several RESPECTED carburetor people that cannot agree. How many pixels have we disturbed to come to no consensus???

Wonder how much Rochester spent in non-productive time, and postage answering the question.

From my standpoint, I really don't care. I will continue to build our kits with the latest bill-of-material I have for each carburetor. But if someone has their mind made up that the vented ones should be used in these carbs, and really doesn't mind a few extra bucks, let me know when you order, and I will include BOTH!

We have both gaskets made in the USA, and I do production runs of 500 each at a time. I am not going to run out of either.

Jon.

[sixty8ragtop]

Superior knowledge and service. Great kits and rebuild services. Ron and Tim Hewitt at Daytona Parts Co., 1191 Turnbull Bay Road, New Smyrna Beach, FL 32168 (386) 427-7108. https://daytonaparts.com/?gclid=CJGu...FRY7gQodZX8C8Q

[Tom Vaught]

I have always used the vented gaskets as my 64 GTO was a KC Built car and has never "gone west". No need to worry about massive sand dust storms in Michigan (or Missouri).

Tom V.

But Carb Engineers did stuff for a reason and it would be nice to pin-point that reason.
If it was a "Hot Start Fix" that was adapted across the board or otherwise, fine with me.

[Kenth]

Originally Posted by Tom Vaught

If it was a "Hot Start Fix" that was adapted across the board or otherwise, fine with me.

The "hot start fix" would be using the vented gasket according to the document Jon posted.

All the other GM Tripowers uses vented gaskets, due to that reason, but Pontiac went from a vented gasket to a non-vented gasket for the end carbs, wich i find somewhat odd.

[Dick Boneske]

I have always thought the vented gaskets were important for the end carbs in case the throttle plates leaked slightly. I thought, in that case, the air sucked past the plates would flow through the vents and not so much past the venturi cluster, causing nozzle drip if there was a lot of leakage.

In the center carb, I don't see an advantage to the vented gasket, since there is always air flow past the throttle plates at idle and above. The added air that leaks in through the vented gasket would lean the overall mixture slightly, but not a significant amount.

The discussion of vented base gaskets reminds me of the question I've always had about the small (.027") holes in the throttle plates on '64-'66 end carbs. Why are they there?

[Tom Vaught]

Originally Posted by Dick Boneske

The discussion of vented base gaskets reminds me of the question I've always had about the small (.027") holes in the throttle plates on '64-'66 end carbs. Why are they there?

As you know the throttle blades on the end carbs rest on the walls of the bores.

I was told one time, (and it may be pure bs), that when the engine is cruising down the road under a moderate to higher vacuum that the end carb throttle blades would still see a vacuum under them if they were solid plates and you went to WOT quickly. Therefore more force on the linkage required to open the blades.

But with the small 0.027" holes in the blades, there would always be some reduced vacuum under the blades and the blades would see less resistance as far as opening goes.

In some ways it makes sense but not having access to vacuum probes and a very accurate Carb test stand, I cannot say one way or the other. What do you think of the concept Dick?

Carb Engineers do stuff for reasons.

Tom V.

[Dick Boneske]

Tom,

It must be something like that as a reason for the small holes. Sure would be nice to be able to talk to one of the engineers involved in the design of these carbs. I wonder if any of them are still around.

[barrierblue66]

I know a guy who was an engineer that worked on the Rochester's. I may see him Friday.

1963 Catalina Safari, Silverleaf Green, Cameo Ivory
1966 Grand Prix, Marina Turquoise

[barrierblue66]

Talked to my friend last night and he replied:

I reviewed our discussion last night with a fellow carb engineer I worked with and we agree - the forum explanation is not correct.* No way a .027" hole can do anything with the vacuum load on the valve.* My thought that is that is is there to simply prevent a flooding carb to spill onto the manifold is valid to us. * The size will pull fuel thru it but not enough to stall the engine but enough to make you aware of a problem.

1963 Catalina Safari, Silverleaf Green, Cameo Ivory
1966 Grand Prix, Marina Turquoise

[Tom Vaught]

"My thought that is that" says that he does not know the answer either.

Or he would post "This is what the function of the hole is and why it is there".

Tom V.

[Tom Vaught]

Found this in a old carb manual:

"Although the idle mixture is controlled by adjustments on the carburetor, the BASE MIXTURE (and the mixture ranges that are possible) depend on the balance between the amount of air flowing through the hole in the throttle plate and the amount if air/fuel coming through the Idle Circuit. The correct Air/Fuel mixture at idle is different depending on what the idle ignition timing is, and that in turn is different between different carburetor systems and distributors."

So the small holes in the throttle blades are there to "balance the air vs fuel" at idle. Has nothing to do with "preventing a flooding carb ........."

Tom V.

[Kenth]

I don´t see that the small, .027" holes in the end carbs throttle blades would have too much with "balancing the air vs the fuel" to do, not even at idle speeds.
This would be obtained with with larger holes in the center carbs throttle blades.

I would say that the small .027" holes are there to keep the throttle blades clean from excessive fuel vapors clogging the blades circumference.

At least, this is what i´ve found.

[Tom Vaught]

Obviously you and I both know that the last post I made was in reference to the holes in the center carb as it is the only one that has a idle circuit where you can "balance the air vs the fuel" as the END CARS DO NOT EVEN HAVE IDLE CIRCUITS.

If your post is assuming a "varnish like substance" coating the edges of the blades and causing them to stick, I am open to hearing the logic behind that deal with the bleed holes.

Tom V.

[Kenth]

Tom, as we have discussed the outer carbs bypass air holes for quite a while, i wasn´t shure what you refered to when you wrote;

"So the small holes in the throttle blades are there to "balance the air vs fuel" at idle. Has nothing to do with "preventing a flooding carb ........."

Usually the idle bypass holes in the center/single carbs throttle blades are much larger than .027", and then used to keep the thottle blade edges in correct position to the off idle slots/holes.

And yes, i´m assuming fuel vapors will make a "varnish like substance" coating on the edges of the outer carbs blades and causing them to stick over time, unless they are ingested for combustion by the .027" holes, for folks that won´t go WOT too often.