I have a Holley 4 barrel on my 70 chevelle. The car seems to run fine on acceleration but it seems to idle rough. Also, at normal speed going down the road, I seem to feel a hesitation. Is it possible that it needs adjustment? Can someone tell me how or point me toward a book or information. Thanks!

Hi bhbw,
H.P.Books sells a couple of books on Holley carbs that should tell you anything you need to know about them. One is called "Holley Carburetors" and the other book is "Holley Carburetors & Manifolds"
They have a lot of the same info in both books so it wouldn't matter which one you get.
They can be found at speed shops, big book stores, and at automotive type swapmeets.
Check the basics first, like float level and vacuum leaks.
GaryR

Holley carb setup.

Mixture Screws: Turn clockwise until the engine starts to stumble and backout screw 3/4 turn.

If your cruising and the car feels like it's surging then ritchen (turn counter clockwise)
the air/fuel mixture screws 1/16" on both sides and go for a drive. Do this until the surge
is gone.

Some guys like to turn the screws out (richen) until they get the highest vacuum reading or highest rpm but I think this ends up being too rich. You can smell the fuel at the tail pipes at idle.

You should have set up the following:

1. At wide open throttle the pump lever should be set to .015 of an inch (feeler gauge).

2. Secondary throttle stop screw adjustment must be set as follows: back off adjustment
screw until the throttle plates are fully closed (secondaries). Turn adjustment screw
until it just touches the throttle lever and turn 1/2 turn more to position the valves.

3. Float level should be to the bottom of the site screws while car is running.

4. Set idle at 800 rpm or 1000 or what ever your specs call for.

5. You should start off having a yellow secondary diaphram spring to see how fast the
secondaries are opening.

Holley Vacuum Secondary Spring Info:

350 CID Engine
Spring colour RPM to Open RPM at Full Open
Yellow (short) 1620 5680
Yellow 1635 5750
Purple 1915 6950
Plain (Std.) 2240 8160
Brown 2710 8750
Black 2720 not fully open at max air flow

All data taken without air cleaner. An air cleaner would cause earlier opening in all cases.


402 CID Engine
Spring colour RPM to Open RPM at Full Open
Yellow (short) 1410 4960
Yellow 1420 5020
Purple 1680 6050
Plain (Std.) 1960 7130
Brown 2380 7650
Black 2390 not fully open at max air flow

All data taken without air cleaner. An air cleaner would cause earlier opening in all cases.