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Discussion Starter #1
I am trying to tune my 600 cfm Holley 4 bbl and am not sure if I am doing it right. I have set the secondaries and choke Idle (??). I started by turning in the mixture screws JUST until they seated. I then fired up the motor (1000RPM) and started turning the screws clockwise. Nothing changed! RPMs, idle all stayed the same. I thought maybe I was turning the wrong way, so I started turning clockwise. Only after I got both screws seated, did the RPMs drop. Is the choke idle or secondary idles set incorrectly?? Please Help!!
 

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Well first we need to know if its a double pumper (mechanical secondaries) or vacuum secondaries..

you should seat your mixture screws (two of them) and then unscrew them about 1.5-2 turns or so.. its not crucial.. then turn your idle SPEED down to zero..(one screw on the linkage) then turn the speed screw in a little bit so you just barely have it opening the throttle.. too much and you will disable your idle system.. too little and it wont run.. from there get it running, probably wont idle real great and set your idle speed to 650-750 rpm or so (in neutral w/ manual trans, in gear with auto)

then (in neutral with both trannies) play with your mixture screws again until you get the fastest idle but no more than that.. then back them off 1/8 to 1/4 turn... do one a little at a time.. and go back and redo each side until they are both perfect.. MOST holley carbs idle mixture screws are
CLOCKWISE-> LEAN (less fuel)
COUNTERCLOCKWISE-> RICH (more fuel)

a few factory installed holley's were reverse that but its unlikely..

if this stuff still doesnt have an affect on your idle than you have other problems... check your float levels, make sure theres no vacuum leaks... let us know how it turns out

Mike
 

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Discussion Starter #3
Mike,

I have vacum secondaries. I have the idle speed screw backed all the way off. When I adjust the mixture screws, I notic no change in idle or RPMS anytine while turning them. The motor starts and idles fine but I think it idles too high. I just cant figure out why adjusting the idle screws makes no change. Thanks.
 

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Quik,
If you have the idle screw backed off all the way so that the throttle plates are completely closed, and you still have a fast idle, you probably have a vacuum leak somewhere. The motor should not run with the throttle plates closed all the way. One commonly missed item is the large vacuum fitting on the rear of the carb at the bottom. If not plugged, or hooked to power brakes etc, it will cause a very fast idle.
You mentioned "choke" idle ? Are you referring to the fast idle cam ? You really should be adjusting every thing after the motor is fully warmed up and the choke is open. You also mentioned "secondary" idle. I am not sure what you are referring to here, unless you messed with the small screw that opens the secondary throttle plates at idle. If you did, you should put it back to the factory setting as it is normally not neccessary to mess with it and it could be causing your problem also.
Mike described the adjustment pretty good, the throttle plates should be just barely open, and the primary mixture screws out about a turn or so. From this point it is a back and forth type adjustment. If you are going to run Holley's it really would be a good idea to get one of the many excellent books on the subject. They really help.


------------------
Bill Koustenis
Advanced Automotive Machine
Waldorf Md



[This message has been edited by BillK (edited 06-03-99).]
 

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speaking of chokes, make sure your choke is fully open and your fast idle cam isnt kicking the idle up at all. that would cause the problems you are experiencing

Mike
 

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Discussion Starter #6
Thanks guys, I will check for vacum leaks tomorrow. The secondary idle I refer to is the sec. throttle plates. These had to be adjusted while the carb was off using the screw. I followed the info provided in the Haynes Holley book. I will also check the choke as I also set those adjustments using the book. I have noticed that the motor REALLY increases idle when I close the choke, but after a few seconds closed it will die. Thanks again, Carbs are not my strong area and this is my first motor rebuild.
 

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Holley carb setup.

1a. At wide open throttle the pump lever should be set to .015 of an inch (feeler gauge). Undo your throttle return string if your doing this on the car. Have a friend pull back and hold throttle lever wide open as if the gas pedal is floored or tie it down but make sure it's still wide open.

1b. Using a long slot screw driver push down on the pump lever hard and hold while using your other hand measure with a feeler gauge the space between the lever and the pump adjusting nut.
If you need to adjust then let go of everything and adjust the nut to get .015. Hold the bottem nut and turn the top nut clockwise to compress spring and make the gap bigger or counter clockwise to make the gap smaller.

2. Secondary throttle stop screw adjustment.
Must have carb off car. 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 While car is running.
Float level should be to the bottom of the fuel bowl site screws. Loosen lock screw a bit and hold then turn nut clockwise to lower float level or counter clockwise to raise. 1/4 turn makes float move 3/16". You can give the accelerater shot to hurry up the change you made.

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

5. Secondary diaphram spring. You should start off having a yellow secondary diaphram spring to see how fast the secondaries
are opening. Don't need the chrome ball. If your racing leave it out.

6. Mixture screws.
Turn in 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.
I know you probably don't have a surge problem but keep this in mind for future problems.
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 which means your too rich unless your car won't idle unless your on the rich side.

The 1970 manual for a 396/375 or 454/450 front jets should be 70. Rear should be 76.

Hlley 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.

Mark
 
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