Holley Accelerator Pump Covers -4 variations

[Gerard F.]

with the same Holley part number.

Getting back to my carburetor project after a little hiatus over the holidays.

Here's my collection of Accelerator Pump Covers taken from various 65-68 Holley carbs:




Funny, these covers all share the same basic Holley part number, 34R-2178, yet there are 4 different configurations, 5 if you want to count the difference in screw heads (slotted vs phillips)

From left to right they are:

1. Flat cover with beveled screw holes for clutch head screws
2. Flat cover with corners recessed, came with short phillips screws
3. The two in the third column have flat covers with the bolt heads protruding. The upper one came with phillips screws on a later carb, the lower one came with slotted screws on an earlier carb.
4. The one on the far right came from a later replacement 3810 and has a B after the part number. The rounded configuration with recessed corners seems to be common to later and current replacements for most Holleys.

The single digit number under the part number, seems to me, to be a casting mold number, as it doesn't seem to have any rhyme or reason as to the configuration.

Are there other configurations of this part number?

Can anyone identify the years of the first three columns indicated above.

Which pump cover would you use on a late June 67 3810?

[Terry M.]

Re: Holley Accelerator Pump Covers -4 variations

Not much help to you, but my 1970 came with clutch head screws. I still have the screwdriver I had to buy to try to stem the tide of fuel seeking freedom. I can find the cover configuration in a couple of days when I get done with a small road trip if you think it would be useful to you.

[Timothy B.]

Re: Holley Accelerator Pump Covers -4 variations

Jerry, My dated 3810 came with your example #2. I am curious about the same question..

[Joe L.]

Re: Holley Accelerator Pump Covers -4 variations

Not much help to you, but my 1970 came with clutch head screws. I still have the screwdriver I had to buy to try to stem the tide of fuel seeking freedom. I can find the cover configuration in a couple of days when I get done with a small road trip if you think it would be useful to you.

Terry-----

Yes, the Holley carb on my 1968 Chevelle SS L-78 used clutch head screws in a variety of locations, including the accelerator pump. I can recall looking all over Los Angeles for a clutch head screw driver when the carb failed on me on a vacation trip in the summer of 1968. The car was only a few months old but the local Chevrolet dealer (Citizens Chevrolet on Colorado Bl. in the Eagle Rock district of Los Angeles) told me that the carb only had a 90 day guarantee and I was just past that.

I found clutch head screw drivers but I never found one of the correct size-----all were either just too small or just too big. Finally, I went to a carburetor shop and asked the guy there if I could use his. He told me that he'd never been able to find one, either. Then, he showed me how he just used a regular, flat bladed screwdriver by jamming it in the clutch head and turning. That solved my dilemma.

This whole situation, and especially the failed carb after only a few months of use, is one of the early-on things that caused me to develop a "prejudice" towards Holley carbs. I had to rebuild the carb a few more times before I finally sold the car in September, 1969 with less than 20,000 miles on it. I shed no tears when the new owner drove it away. Less than an hour later I was driving my new 1969 Corvette. What a complete joy the Q-Jet turned out to be. Not without any problems over the years, but very bearable compared to the Holley.

[Clem Z.]

Re: Holley Accelerator Pump Covers -4 variations

with the same Holley part number.

Getting back to my carburetor project after a little hiatus over the holidays.

Here's my collection of Accelerator Pump Covers taken from various 65-68 Holley carbs:




Funny, these covers all share the same basic Holley part number, 34R-2178, yet there are 4 different configurations, 5 if you want to count the difference in screw heads (slotted vs phillips)

From left to right they are:

1. Flat cover with beveled screw holes for clutch head screws
2. Flat cover with corners recessed, came with short phillips screws
3. The two in the third column have flat covers with the bolt heads protruding. The upper one came with phillips screws on a later carb, the lower one came with slotted screws on an earlier carb.
4. The one on the far right came from a later replacement 3810 and has a B after the part number. The rounded configuration with recessed corners seems to be common to later and current replacements for most Holleys.

The single digit number under the part number, seems to me, to be a casting mold number, as it doesn't seem to have any rhyme or reason as to the configuration.

Are there other configurations of this part number?

Can anyone identify the years of the first three columns indicated above.

Which pump cover would you use on a late June 67 3810?

the reason for some of these changes was that some of the pump cover would hit on certain intake manifolds and cause a vacuum leak or cause the base plate to be cracked when you tightened up the carb on the manifold.

[Gerard F.]

Re: Holley Accelerator Pump Covers -4 variations

Jerry, My dated 3810 came with your example #2. I am curious about the same question..

Tim,

The *2 was the one I was going to use on this June 3810. It is exactly like the one on the 751 3810 that's on the car.

Just couldn't stand having two unfinished accellerator pump covers, so I refinished them this afternoon with the screws. Here's my collection now:



Incidentally, those clutch head screws are the same screws used to attach the secondary metering plate to the body.

Well, it looks like next week for the throttle body assembly, and then final assembly.

[Timothy B.]

Re: Holley Accelerator Pump Covers -4 variations

Lookin good Jerry,

Before you assemble the metering block and metering plate check the idle jet and PVCR with you pin drills and let me know there size.

[Bill M.]

Re: Holley Accelerator Pump Covers -4 variations

I found clutch head screw drivers but I never found one of the correct size-----all were either just too small or just too big. Finally, I went to a carburetor shop and asked the guy there if I could use his. He told me that he'd never been able to find one, either. Then, he showed me how he just used a regular, flat bladed screwdriver by jamming it in the clutch head and turning. That solved my dilemma.

Joe:

Too late for you, but I just measured the clutch head driver I bought decades ago for the clutch head screws on my 780 Holley accelerator pump. It is 5/32, and I found one at Vintage Trailer (on the web)...in case someone else needs one. The right tool alows you to over-torque that leaky sucker.

Bill

[Gerard F.]

Re: Holley Accelerator Pump Covers -4 variations

Lookin good Jerry,

Before you assemble the metering block and metering plate check the idle jet and PVCR with you pin drills and let me know there size.

Tim,

I did check all the pinholes, here's what I found:

Main Body Air Bleeds: (in air horn)

Primary High Speed (Inner) .028" #70 bit
Primary Idle (Outer) .070" #50 bit
Sec High Speed (Inner) D/S .0225" #74 bit P/S 0" undrilled*
Sec Idle (Outer) .031" #68 bit
* this is the second time I found undrilled air bleeds on a 3810, checked it with compressed air to be sure

Secondary Metering Plate:

This one had a #19 metering plate with top Idle feed holes of .028, and bottom main jet holes of .070,

Correct is a #22 metering plate with .028 top/.076 bottom. I have a new NOS #22 to replace the #19.

Primary Metering Block (4743):

Main Well Air Bleed (top hole) .028" #70 bit*
Idle Circuit holes (bottom) .031" #68 bit*
PVCR .039 #61 bit*
Main Jets were #66, will use #65
PV Unknown existing, will use a 6.5

*I did drill the one blocked Sec High Speed Vent .0225" and the Primary Block checks against 2 other blocks (4743 and 4608) that I have.

Also so the throttle body has the idle pinholes in both secondary and primary barrels (.020"). One on the secondary side was blocked so I freed it up with a drill bit.

Tested everything with compressed air to blow out any debris or glass beads.

[Timothy B.]

Re: Holley Accelerator Pump Covers -4 variations

Thanks Jerry,

Sounds like everything is in spec. Where did you but those small drill bits??

[Gerard F.]

Re: Holley Accelerator Pump Covers -4 variations

Thanks Jerry,

Sounds like everything is in spec. Where did you but those small drill bits??

Tim,

Most hardware stores have them, try ACE or TruValue. Take a look in the section where they have micrometers, because you will also need one of those to check the thickness of the bit (since they are easily mixed up and have no discernable markings)

One set comes in a round case and is pretty pricey. The ACE set is flat and you can take one bit out at a time, and is a little cheaper. But you still need the micrometer and a conversion chart to the bit #.

[Timothy B.]

Re: Holley Accelerator Pump Covers -4 variations

Thanks Jerry,

The drill bits are on my list because I want to verify air bleed and IFR sizes before putting my carburetor back together.

I look forward to hearing how your 3810 carburetor runs on the car. I can't believe the air bleed on the secondary was never drilled. Bet that thing got rich fast under accelleration.

[Clem Z.]

Re: Holley Accelerator Pump Covers -4 variations

Thanks Jerry,

The drill bits are on my list because I want to verify air bleed and IFR sizes before putting my carburetor back together.

I look forward to hearing how your 3810 carburetor runs on the car. I can't believe the air bleed on the secondary was never drilled. Bet that thing got rich fast under accelleration.

they are also a siphon break and if not drilled they can cause the fuel to keep running after the engine is shut off