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Old 12-04-2007, 05:39 AM   #1 (permalink)
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Holley accelerator pump cam mounting positions

I don't get it. The descriptions I have read make no sense.
eg: From this page: Holley Carburetor - Adjusting the Accelerator Pump Circuit for Greater Performance
Accelerator pump cams can be swapped with those of different profiles (change in duration and lift; you know the drill). In addition, the cams have two different mount locations. This allows you to toy with the pump cam without swapping it for another. To change location of the cam, the small screw is removed and then replaced in the second hole.

OK. I have a 750 Vac P/N 80508S with a 30cc accelerator pump and a GREEN pump cam. The pump cam has TWO positions and the carb arm has TWO screw hole positions. The two holes in the cam line up directly with the two holes in the carb throttle arm, which defeats the purpose and renders all instructions I have read ambiguous.

Now, what I don't get is that all the instructions say to: "change location of the cam, the small screw is removed and then replaced in the second hole. "
This has NO EFFECT other than moving a SCREW from one hole to the other as they BOTH LINE up exactly.
Please, can someone decipher the "Holley speak" B.S. and tell me what exactly is meant by "moving a screw to the other hole"
As far as I can make out there is FOUR possible ways to mount the cam.
AM I missing something?
How do I go from standard position hole 1 on both to 2nd position (hole 2) that actually does something other than move a screw? I assume the cam gets rotated but HOW? What does it look like? Which screw hole is used on each part (carb arm and cam)???? Another ambiguous piece information from Holley and the like!!!! Grrrrrrrrrrrrrrrrrr
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Old 12-04-2007, 08:45 AM   #2 (permalink)
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Re: Holley accelerator pump cam mounting positions

If memory serves me, if you look at the arm, you will see two holes, one with the screw in it but through the second hole you will not see a hole in the cam. You remove the screw and rotate the cam until the hole in the cam is under the second hole in the arm. This is the first adjustment.

If that doesn't work, remove the screw and turn the cam until the hole in the cam lines up with the first hole in the arm. This would be the second adjustment.

If that doesn't work, you remove the screw and rotate the cam until the hole in the cam is under the second hole in the arm. This is the third adjustment. Repeat one more time until the screw is back in the first hole and you have gone through the entire cam adjustment for the accelarater pump.

You are correct that with two holes in the arm and two in the cam you would have many possibilties, but move it one hole at a time, and if that doesn't work go to the next. If you have the same success I did with the last two Holleys I bought, you will still have problems. I had to call Holley tech service three times to get the thing close to where it would idle and run well enough. I had to remind the tech guy that this is a new carb and as far as I am cocerned, it should run right out of the box and only require tweaking to schieve higher performance. I now use Edelbrock exclusively, but I am sure there are those out there with horror stories about Edelbrock.

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Old 12-04-2007, 10:25 AM   #3 (permalink)
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Re: Holley accelerator pump cam mounting positions

The holes shouldn't line up perfectly... the holes in the cam are usually about 65 degrees apart where the holes in the throttle linkage should be about 60 degrees apart (those numbers might be a little off, it's been a while)... so using the 2nd hole should require the cam to be rotated 'forward' 5 degrees, 'advancing' the cam, changing the working profile.

Are you sure both holes line up exactly? Like you could put a screw in both holes at the same time? It shouldn't be that way. Also, from my experience the green cam maxes out a 30cc pump, I'd be afraid to leave it on for more than just testing without upgrading to a 50cc pump. It just seemed like the pump was stretched to it's limit, and I wouldn't want to tear the pump diaphram, that's a fire hazard.
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Old 12-05-2007, 02:45 AM   #4 (permalink)
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Re: Holley accelerator pump cam mounting positions

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Originally Posted by Motorhead View Post
The holes shouldn't line up perfectly... the holes in the cam are usually about 65 degrees apart where the holes in the throttle linkage should be about 60 degrees apart (those numbers might be a little off, it's been a while)... so using the 2nd hole should require the cam to be rotated 'forward' 5 degrees, 'advancing' the cam, changing the working profile.

Are you sure both holes line up exactly? Like you could put a screw in both holes at the same time? It shouldn't be that way. Also, from my experience the green cam maxes out a 30cc pump, I'd be afraid to leave it on for more than just testing without upgrading to a 50cc pump. It just seemed like the pump was stretched to it's limit, and I wouldn't want to tear the pump diaphram, that's a fire hazard.
Thanks for the replys. Green is the standard cam for my carb. I thought it was BLACK until I took it right off and put it in the light and saw 290 on it. I have had it for 4 years now. Started to develop a bog and it turned out just to be slack in the accelerator cable. All is good now, thanks
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Old 12-05-2007, 04:57 AM   #5 (permalink)
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Re: Holley accelerator pump cam mounting positions

Pinkies are the standard on every carb I have seen.

If you had a greenie, then someone had that box open before you got the carb, or they just made a mistake at thefactory... But not sure why they would have green cams on the assembly floor?

If it is a double pumper, was the rear cam also green or was it pink?

The green cam is a very agressive cam, and should not be used for 90% of the applications.

If your bogging at launch, the reason maybe your getting too much pump shot from the greenie...
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Old 12-05-2007, 05:31 PM   #6 (permalink)
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Re: Holley accelerator pump cam mounting positions

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Pinkies are the standard on every carb I have seen.

If you had a greenie, then someone had that box open before you got the carb, or they just made a mistake at thefactory... But not sure why they would have green cams on the assembly floor?

If it is a double pumper, was the rear cam also green or was it pink?

The green cam is a very agressive cam, and should not be used for 90% of the applications.

If your bogging at launch, the reason maybe your getting too much pump shot from the greenie...
Its a 750 VAC 80508S Holley factory rebuilt and the cam hasn't been changed since I got it
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Old 12-05-2007, 07:05 PM   #7 (permalink)
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Re: Holley accelerator pump cam mounting positions

I love the great mis conception of "Out of the box performance". If ANYONE out there tells you that you can get a new carb, boolt it on, and every thing will be great is full of shiza.
I buy all my carbs from DaVinci performance, they are BASE LINE set up to my application and dyno ran to be sure they are leak proof and have no surprises. When I get it I talk to Dave and do the final set up on it my self .
There is NO WAY unless your carb is bought and ran on the pump, that it will be spot on right out of any box when received.
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Old 12-06-2007, 12:26 AM   #8 (permalink)
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Re: Holley accelerator pump cam mounting positions

Unless you have an extensively modified engine or you want the carb fine tuned to your engine/ car application you can buy the correct Holley carb for your application, bolt it on, adjust the idle and drive it.
You cannot do this with some modified and most racing engines. The carbs are tuned to general CFM applications within certain hp ranges. Within those ranges the carbs will function reasonably well.
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Old 12-07-2007, 02:33 AM   #9 (permalink)
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Re: Holley accelerator pump cam mounting positions

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Unless you have an extensively modified engine or you want the carb fine tuned to your engine/ car application you can buy the correct Holley carb for your application, bolt it on, adjust the idle and drive it.
You cannot do this with some modified and most racing engines. The carbs are tuned to general CFM applications within certain hp ranges. Within those ranges the carbs will function reasonably well.
Apparently the 80508S I have is THE carb for a particular 430HP small block Chev crate motor.
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Old 12-07-2007, 02:11 PM   #10 (permalink)
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Re: Holley accelerator pump cam mounting positions

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Originally Posted by PaulS1950 View Post
Unless you have an extensively modified engine or you want the carb fine tuned to your engine/ car application you can buy the correct Holley carb for your application, bolt it on, adjust the idle and drive it.
This is very true, however there is a BIG difference between "drive it" and "run optimally". The metering can be quite a ways off, usually on the richer side, without any discernable loss in driveability. And just because you take it to a dyno and your WOT comes out to a perfect flat 12.5:1 doesn't mean jack about how it's running when you're driving down the road. Unfortunately, most all except for the high-end carbs don't have the tuneability necessary to fine-tune the cruising conditions, such as replaceable air bleeds, idle feed restriction, etc... but since most people don't have a wideband O2 or 4-gas machine, they'll never know the difference, and what the engine is REALLY capable of in regards to maximum street driveability and economy.

So yes, there IS such a thing as bolt-on-and-go, but that only applies to people that aren't too particular about exactly how well the carb is really tuned.
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Old 12-07-2007, 11:49 PM   #11 (permalink)
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Re: Holley accelerator pump cam mounting positions

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Originally Posted by Motorhead View Post
This is very true, however there is a BIG difference between "drive it" and "run optimally". The metering can be quite a ways off, usually on the richer side, without any discernable loss in driveability. And just because you take it to a dyno and your WOT comes out to a perfect flat 12.5:1 doesn't mean jack about how it's running when you're driving down the road. Unfortunately, most all except for the high-end carbs don't have the tuneability necessary to fine-tune the cruising conditions, such as replaceable air bleeds, idle feed restriction, etc... but since most people don't have a wideband O2 or 4-gas machine, they'll never know the difference, and what the engine is REALLY capable of in regards to maximum street driveability and economy.

So yes, there IS such a thing as bolt-on-and-go, but that only applies to people that aren't too particular about exactly how well the carb is really tuned.
Have I ever built a carb for you? You sound like a guy that ran road-race courses and I tuned his carb so that he didn't even need to have a a working accelerator pump. That was the nicest running carb I ever did. Most guys just want to accelerate without a bog, which can be hard to do on a flat bottom, but it is a lot easier and quicker than tuning IFR, PVCRs, HSABs and IABs. Most often tuning a carb just means jets, power valve and at most power valve Channel restrictions. Only a real driver whats a carb tuned to the level that you are alluding to.
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