“Getting Back to the Basics”

So you just bought a new Holley at the local speed shop, what do you do now? Should you just bolt it on and fire that beast up? It's new, why would I want go through it before using it? Is going through a carb something I can do myself? About now you have a lot of questions and choices. Even though the carb is brand new and still in the box I don’t recommend just bolting it on.

Let’s start with that new out of the box carb. The first thing you should do is sit down with the carb in front of you and read all the written material and view the video if one is provided. The idea is to get comfortable with your new carb, pay close attention to little things like the proper way to hook up the throttle linkage and what to adjust and what to leave alone when you first fire up your engine. (On a new engine that has never been run, try to avoid using a new untried carb for the initial fire-up and break-in. The last thing you want to do is run into carb problems that could be detrimental to your new mill at this most critical point in its life span.)

You want to verify the carb was adjusted properly to factory specs before it was put in the box and set on the display shelf at your favorite speed shop. Like everything else these day’s quality control issues seem to arise more than they should. Little things like float adjustment, the initial idle mixture screw settings and proper throttle blade adjustment can make the difference in a carb that runs well out of the box and one that doesn’t. The hardest carb to tune is the one that isn’t set to factory specs from the start. Manufacture’s wants you to be happy with their product and have gone to a great deal of effort to make your carb perform for you. This may sound like a contradiction to my quality control statement, but really isn’t if you realize the tech on the assembly line may have had a few too many last night of just having a bad day for some reason! I have also run across many float bowls in new carbs with small scraps of metal from machine work when the carb was being built.

It's in your own best interest to pull the float bowls off the carb and check and clean them out. This will allow you to check the float level by checking what is referred to as “dry adjustment”. Make sure you have ample room to lay out (in order for ease of assembly) any parts you may take off the carb. Pay close attention to the accelerator pump linkage as well, it will also make re-assembly easier if you know how things fit. Be careful not to damage any gaskets and this also is a good time to replace the factory bowl gaskets with reusable gaskets if you think you may be doing some performance jet changes down the road. Here is a list of what I find are the most critical and should be checked.

1. Pull the float bowls and check for foreign material. Invert the bowl and the float should hang exactly in the middle of the bowl. You can also check your power valve rating and verify what size jets are installed for future reference.

2. At wide-open throttle the accelerator pump lever should be set to .015 of an inch clearance.

3. Secondary throttle stop screw adjustment must be set as follows: back off adjustment screw until the secondary throttle plates are fully closed. Turn adjustment screw until it just touches the throttle lever and turn 1/2 turn more to position the throttle blades properly. Note: If you have a 4 corner idle skip this step and follow step 4 for both primary and secondary throttle blade adjustment.

4. Verify or adjust the primary throttle screw so the transfer slot in the throttle bore is uncovered by about .020”

5. Verify or adjust the rich lean mixture screw settings. Turn them in and count the turns to verify them, you want them about 1 ½ turn out to begin with.

Important: always use the manufactures recommended settings in place of the ones I mention if they differ.

You are now ready to bolt up your carb and make all the necessary connections, again following the manufacture’s instructions. Be sure to watch for leaks, fuel being the most critical but air also. A vacuum leak can cause all kinds of problems. Warm the engine up properly before making any adjustment to the idle, the idle mixture or the float level. If all went well you should have a good base to start tuning. Drive the car and make note of any bogging or stumble and the conditions that cause it. More on actual carb tuning later. Keep a journal and record base settings and each change you make as well as how it effected the way your engine runs. Next time, we’ll look at that used swapmeet carb.

References:
http://www.holley.com/TechService/Library.asp
Copyright © DjD 2003