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  #16 (permalink)  
Old 07-09-2008, 01:20 PM
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Quote:
Originally Posted by 302 Z28
Mechanical secondaries do not belong on a street driven car unless you own a gas station. There is no performance gain from running mech secondaries on a street engine, quite the contrary in fact.

Vince

Completly untrue and way too simplistic.. It seems to me that most remarks like that are based on the assumption that we are comparing typical "performance (holley/demon) carbs.

The bottom line is that vaccuum secondaries are reccomended for the average Joe because they are automated.

There are lots of different carbs in both categories, an old Carter 450 with mechanical secondaries will get a lot better mileage than a Holley 850 with Vaccuum secondaries on nearly any application.

For most situations I agree that Vaccuum secondaries are hard to beat for street use, but that doesnt mean that mechanical is a bad idea.

It mostly depends on the specific application and how it is tuned and driven.

If there were no performance gain to be had from using mechanical secondaries then they wouldnt be the dominant carburetor for strip use.

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Last edited by 65smallblock; 07-09-2008 at 01:44 PM.
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  #17 (permalink)  
Old 07-09-2008, 01:25 PM
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Quote:
Originally Posted by 65smallblock
There are lots of different carbs in both categories, an old Carter 450 with mechanical secondaries will get a lot better mileage than a 850 double pumper with Vaccuum secondaries on nearly any application.
A double pump would be a mechanical secondary. A Vacuum secondary carburetor only has one pump.

Quote:
Originally Posted by 65smallblock
For most situations I agree that Vaccuum secondaries are hard to beat for street use, but that doesnt mean that mechanical is a bad idea.

It mostly depends on the specific application and how it is tuned and driven.
Very Well Said!


Quote:
Originally Posted by 65smallblock
If there were no performance gain to be had from using mechanical secondaries then they wouldnt be the dominant carburetor for strip use.
Exactly...
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Old 07-09-2008, 01:31 PM
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Quote:
Originally Posted by CarbGuy
A double pump would be a mechanical secondary. A Vacuum secondary carburetor only has one pump.



...

Doh!!! (homer simpson smile)
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  #19 (permalink)  
Old 07-09-2008, 01:37 PM
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Quote:
Originally Posted by CarbGuy
Great way to get dead in an emergency...
what do u meen ?
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Old 07-09-2008, 01:44 PM
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Originally Posted by 000882334
what do u meen ?
A throttle that doesn't close all the way is a great way to run through your brakes and possibly crash and or kill someone. Which with a modification like that a good lawyer would make your life VERY bad.
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Old 07-09-2008, 03:05 PM
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Quote:
Originally Posted by CarbGuy
A throttle that doesn't close all the way is a great way to run through your brakes and possibly crash and or kill someone. Which with a modification like that a good lawyer would make your life VERY bad.
i see what ur saying, i havent had this problem ever, maybe it has something to do with driving a stick, cuz i could just put in the clutch and brake or w/e . but if anything close to what ur talking about happens im goin back to original
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Old 07-09-2008, 03:57 PM
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If you are forcing a vacuum secondary carb open by cobbling up the linkage, you really DON'T have a clue as to what you are doing , you will go faster if you take the time to tune it correctly. Can't tell you the # of times I've seen that bonehead move , although I've purchased several used carbs this way for cheap knowing I could fix them.
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Old 07-09-2008, 04:18 PM
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Quote:
Originally Posted by ericnova72
If you are forcing a vacuum secondary carb open by cobbling up the linkage, you really DON'T have a clue as to what you are doing , you will go faster if you take the time to tune it correctly. Can't tell you the # of times I've seen that bonehead move , although I've purchased several used carbs this way for cheap knowing I could fix them.
its working fine for me, but im new to the carb thing, i just rebuild me holley 4160 and have been fine tuning it since, its super responsive right now and has a good mix, but what is the "by the book" way to do adjust the vac secondaries ? i appreciate the criticism and comments, i am learning a lot from them, but thats just how i do things (trial and error)
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Old 07-09-2008, 05:24 PM
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This was a long time ago and i ended up goin with a vacuum holley 650. Works real nice except i cant get rid of a small hesitation. BTW, i'm only getting like 10-12 mpg so i guess the fuel efficiency difference between the two doesnt really matter. But then again, every mile per gallon counts these days.
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Old 07-09-2008, 05:31 PM
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Quote:
Originally Posted by mightycarlo10
This was a long time ago and i ended up goin with a vacuum holley 650. Works real nice except i cant get rid of a small hesitation. BTW, i'm only getting like 10-12 mpg so i guess the fuel efficiency difference between the two doesnt really matter. But then again, every mile per gallon counts these days.
hesitation is probably wrong air/fuel mix off idle (ie too much air or too much fuel) , which could be a simple change like a different accelerator pump cam (30 dollar holley kit comes with a whole bunch)
mine did the same thing till i changed this
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Old 07-09-2008, 05:32 PM
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Correct way to adjust Holley vacuum secondarys is to buy the vacuum secondary diaphram spring assortment from Holley or The Carb Shop, and then install the best spring for your combo by road testing it, then track testing.
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Old 07-09-2008, 05:43 PM
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Quote:
Originally Posted by ericnova72
Correct way to adjust Holley vacuum secondarys is to buy the vacuum secondary diaphram spring assortment from Holley or The Carb Shop, and then install the best spring for your combo by road testing it, then track testing.
thank you, ive seen those
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Old 07-09-2008, 07:16 PM
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I've tried different shooters but that didnt seem to help. Its got 35's in now and it had 31's. I'll have to try what you guys are talkin about.
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Old 07-10-2008, 08:44 AM
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The vacuum secondaries on a Holley will not open until the engine can use them. Buy the vacuum spring assortment package and go that route. You might have a timing problem, too, with that hesitation...
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  #30 (permalink)  
Old 07-10-2008, 12:33 PM
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Vacuum vs Mechanical

The overall weight of your ride should determine if you should go with a vacuum secondary or a mechanical. If your ride is heavy you'll want the vacuum , if it's lite ( under 3000 pounds ) mechanical will be an option. The vacuum secondaries will only open as the engine demands the extra fuel and will give you better mileage. The Holley can be tuned with a simple spring change to the secondary , some have a quick change spring attachment that makes it a snap to change springs. Good luck !!
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