[RALPH DUNHAM]

Hello I would like to know why a pontiac 4bl has two cut outs in the secondary blades and olds and buick do not ?? is it somthing to do with the ideling of a pontiac or somthing els ? thank's .

[78w72]

what do you mean "cut outs"? can you post a pic? none of my pontiac q-jets have anything cut out of the secondary plates...

[Greg Reid]

There are people here who can explain this a LOT better than I can....but if you look at the airhorn directly behind the secondary air flaps, you'll see two small fuel supply holes.
Those openings that you are asking about exposed those fuel openings directly to the intake so fuel can be pulled as soon as the secondaries open. Without the openings, no fuel will be pulled until the airflaps open.
There is more than one variation of the openings. One type has the large square openings and another is just a very small half-moon opening and some none at all.
As for why they are on some carbs and not others...Just like anything else, what seems like a good idea to some manufacturers in some years, doesn't in other years.
In fact, I think they did away with them entirely in the mid 70s maybe?

[harry k]

Originally Posted by 78w72

what do you mean "cut outs"? can you post a pic? none of my pontiac q-jets have anything cut out of the secondary plates...

Here you go.

[jonmachota78]

Originally Posted by RALPH DUNHAM

Hello I would like to know why a pontiac 4bl has two cut outs in the secondary blades and olds and buick do not ?? is it somthing to do with the ideling of a pontiac or somthing els ? thank's .

the premise is not true. I have two Pontiac qjets from different years and neither have the cutouts.

[jonmachota78]

Off my Buddys old 72 Bonneville

[78w72]

Originally Posted by harry k

Here you go.

i thought you meant the actual butterflys. regardless, never seen that on any mid-late 70's pontiac q-jets. must be older or somthing oddball.

[Greg Reid]

I have to correct part of my earlier post. I said the two fuel holes were behind the flaps, I meant to say that they are ahead of the flaps.
As to which carbs have them, I have some with and some without. I do think they are primarily on the earlier carbs. I have swapped some onto the carbs I wanted them on.
Also, again, some just have the small scallop out of the leading edge at the holes and some have the large, rectangular cutout. I don't use those.
Finally, some of the carbs have the leading edge of the flaps directly centered on the fuel holes so you don't really need the cutouts. The main thing is that you don't want NO cutout if the fuel holes are completely above the flaps. You get a hesitation in fuel pullover from the holes in that configuration.

[RALPH DUNHAM]

Hello to all thank you for all the help I think I have the anser and an idea thank's

[gtofreek]

I have only seen this in the early performance q-jets. If I had to take a guess, I would say from 67-70, or there about. Like someone else mentioned, it helps to get fuel flow initiated before the air valves open, from the way I see it anyway. I have not seen it on later carbs starting with a 1 in their numbers.

[Jeff Hamlin]

No slots on the 66-67 OHC 6/SPRINT Q-Jets either.

[jamaca85]

I am no expert on this topic but I have seen them in 69-71 q jets. but cliff would be the expert on this....he should know all about it

[Mr. P-Body]

Not brand specific. "Performance" carbs had them, "stocker" and emmissions carbs did not.

The notches are about 5/16" square, directly over the main discharge nozzles in the secondary. the purpose is to allow a small amount of air to pass the nozzles before the air valve opens, creating a lower pressure around the nozzles, getting a "head start" for fuel flow as the valve opens and the metering rods rise.

I'm sure Cliff or others can explain it it more detail, but this is the jist of it. The effect can be realized by drilling 1/4" holes in the same spot.

I have a '79 Olds 350 carb with the notches.

Jim

[67cruiser]

Mostly for air but GM found out later that the cut-outs where to big. I took standard ones off any Buick or Olds and simply put a small knotch in them instead. Under the flaps i then ruffed up the underside with a punch for better flow. seems to work for me.

[GTOLou]

Originally Posted by Mr. P-Body

Not brand specific. "Performance" carbs had them, "stocker" and emmissions carbs did not.

The notches are about 5/16" square, directly over the main discharge nozzles in the secondary. the purpose is to allow a small amount of air to pass the nozzles before the air valve opens, creating a lower pressure around the nozzles, getting a "head start" for fuel flow as the valve opens and the metering rods rise.

I'm sure Cliff or others can explain it it more detail, but this is the jist of it. The effect can be realized by drilling 1/4" holes in the same spot.

I have a '79 Olds 350 carb with the notches.

Jim

I think they are called transition slots -

[gtofreek]

The transition slot is in the throttle body.

[GOAT WHORE]

Originally Posted by gtofreek

The transition slot is in the throttle body.

X2
Two different things.

[Cliff R]

Secondary POE (Pullover Enrichment) is well covered in my book, as are the slotted secondary flaps. They were Pontiac specific, used on most V-8 carbs from 1967 to 1973. Not the best set-up, as they actually allow too much air into the engine when the huge secondary throttle plates first open.

The very best POE set ups were used on the early 455 Buick "high performance" carbs, holes under solid flaps, and the 75-79 Pontiac carburetors having the holes in line with solid flaps so they can see the underside of them. If I had to rate one of these designs as the very best, it would be the set-up found on the 75-79 Pontiac carburetors (301's did not use this set-up).

The large slots found on the early Pontiac carburetors, are a great set-up in theory, but less than ideal in practical application, as with many other things related to this hobby.....Cliff