Style of Holley Accelerator Pump Housing?

[Everett Ogilvie]

I am trying to determine what style primary accelerator pump housing came on Holley four barrel carbs installed by St. Louis, as opposed to replacement Holley carbs (on midyear cars especially, but early Sharks also). There are 3 types of primary accelerator pump housings;

1) "flat" housing body (no recesses on the 4 corners for the mounting screws) that mounts to the fuel bowl with Phillips screws with lock washers. The heads of the Phillips screws project beyond the surface of the pump body.

2) "flat" housing body with countersunk screw holes. Special screws are used on this style - flat, countersunk head with what looks like a clutch head, but a slotted screwdriver fits the head. Lock washers were not used due to the countersunk head, but the angled countersink area on the screw head has "lines/dimples" which lock the screw when tightened. The flat screw heads are completely flush with the housing body when tightened.

3) housing body with recessed corners for each of the 4 mounting screws. Mounts with Phillips screws and lock washers. Because of the recessed corners on the housing, the screw heads do not project beyond the housing body, but are contained with each corner recess (not a countersunk style however).

My 1976 Holley book shows almost exclusively style 3 above, using Phillips screws and the 4 recessed corners. This book has hundreds of photos of "aftermarket" Holley carbs, rather than original equipment carbs, which leads me to believe style 3 is NOT the St. Louis style.

I believe Holley carbs installed by St. Louis on midyear cars used style 1 or 2 listed above, and I am leaning towards the countersunk flush style, at least on big block Holley carbs. I have a 396 3124 carb dated 652 (purported to be a warranty replacement unit), and it has the flush-mounted style housing. The patina and finish make it appear as though it is the original pump housing. Two out of four period-dated 3247 carbs I have owned have had the flush-mounted style.

If there are owners with known original carbs (preferably unrestored, or restored using the specific original parts), can you provide inputs about the style of housing body and fasteners? I realize that most restored carbs encountered utilize the projecting Phillips screws with lock washers, but I think this can be attributed to the fact that those pieces are more common.

[Craig S.]

Re: Style of Holley Accelerator Pump Housing?

Everett - well, I have an original 3247 from my 66 427/425 that I am about to send out to be restored by Jerry Luck or Jerry McNeisch. I just checked for you and it is style 1, flat, no countersinks, screws protruding above the casting. The patina is old and matches the rest of the carb...gold hue is pretty much gone. The pump cover casting has part number 34R-2178 embossed on the face. The cover is attached by slotted phillister head screws, I can say if they are original, but they look like it from the wear and tear. The carb date is 5B1 and my car is a March 66 425...I can't vouch for certain that this is the original carb for the car, but, this is not a restored (yet anyway) car so it is at least period correct....Craig

[Terry M.]

Re: Style of Holley Accelerator Pump Housing? *TL*

Everett,
I vividly remember buying a clutch head screwdriver to use on the accelerator pump screws on the Holley on my 1970 LT1. As to the rest of your questions - I'll have to go into the cold garage and look. Do you have enough data that you want carburetor dates?

[Everett Ogilvie]

Re: Holley Accelerator Pump Housing (LONG)

Thanks Craig and Terry for your responses. The dates on the carbs might be important to help determine if a certain style was used early or late, but it is most likely more complex than that. The 3247 on my '66 is dated 585, but it is restored, so I do not know how it was originally configured. I have personally owned four 3247's (two with each style), but the dates on these carbs and restored/unrestored states are mixed, so my data is completely inconclusive.

The same part number Craig reported is found on both style 1 and 2. However, there is a suffix below the part number - I found a 1 on the countersunk style housing on my unrestored 3124 carb, and a 5 on the non-countersunk style on another 3247 service dated carb. I theorized this number could be an engineering rev of the part, which could make the 1 the earlier part, but I found an 8 on yet another countersunk style housing, so the picture is not clear. These part/rev numbers are "debossed", so they were part of the mold (I think the housing is a cast part).

It appears to me that the housing with the countersunk holes and the corresponding "self-locking" fasteners, would be a more complex/expensive system to make - the housing would need the additional step of machining the countersink, and the fastener is more specialized than the standard fastener and lock washer. I don't think too many manufacturers add cost or complexity to their systems - instead they simplify, so they could have reduced steps by using the same housing and not machining the countersink on the holes and by going to the standard fastener with lock washer. This line of reasoning would imply that early usage consisted of the flush-mounted clutch head type (with the elimination of the countersink later), but it is likely that the style could have been dictated by necessary clearance with the intake manifold on specific applications, so the usage by Holley could be complex. For example, if memory serves, the center carb on tripowers has very little clearance below the accelerator pump - maybe other carb/intake combinations had more clearance.

This "study" is part of a larger interest I have to determine original vs. replacement hardware throughout an entire carb of the period, down to the last screw. For example, the fuel inlet nuts on the bowls - some have two wrench flats in addition to the large hex, and some are simply round, without the flats - which is correct/original to a particular carb? The screws used to mount the secondary vacuum unit on 4 bbl carbs are observed to be either slot head or Phillips - which is original/correct (I think I have the answer to this one)? I believe some carb restorers simply go to the parts well when restoring carbs and you end up with whatever hardware they have on hand - in some cases in place of your original parts. Unfortunately, there are more restored carbs out there than originals, which makes this type of detail verification very difficult, but interesting in my opinion.

[Craig S.]

Re: Holley Accelerator Pump Housing (LONG)

Everett....I checked my 3247 again, it has the 2 mold number below the Holley part number. Your work sounds like the makings of a future Restorer article...Craig

[Chris H.]

Re: Holley Accelerator Pump Housing (LONG)

Everett, my 396 had a service replacement 3124 with a '66 date, and it had style #3 that you mention.

The pump cover always leaked which drove me batty. Turns out the cover was slightly warped from over-torquing the screws. I filed the cover flat, and that was that.

[Terry M.]

Re: Holley Accelerator Pump Housing (LONG) *TL*

OK Everett - yes your work sounds interesting. I'll check my original carb and message you off the board. It will be hard to find a significant number of unrestored carburetors, but sounds like an interesting survey. If you could get some kind of questionnaire or form together and place an ad in The Driveline you might get more responses.
BTW: Snowed here today, so I blew off the garage trip in favor of magazine work. I'll get there and message you.

[Clem Z.]

Re: Holley Accelerator Pump Housing (LONG)

any time you rebuild a holley sand or file the acc.pump cover because it will be warped.

[Terry M.]

[Everett Ogilvie]

Re: Style of Holley Accelerator Pump Housing?

Thank you for all the detail Terry. One thing - rather than the choke pull-off screws, how about the secondary vacuum unit mounting screws? It is these that I believe should be slot head. Indeed, the choke pull-off fasteners I have observed are phillister Phillips as you report, and in contrast, I find it interesting that the secondary vacuum unit usually seems to use 3 slot heads to mount it to the carb main body (on many/most of what I believe are original units). I had a carb restored once and when it came back, it seemed that many of the fasteners had been changed - it was then that I started observing the little details and trying to come up with some general guidelines for original vs. replacement hardware.

[Terry M.]

Re: Style of Holley Accelerator Pump Housing? *TL*

Sorry Everett, reading comprehension is in the dumper today.
Secondary vacuum actuator screws = fillister head slotted, gold with lock washers. Use common screw driver to remove.