Holley Setup





You found the guy who posted the setup for the holley. I've done a lot of work with single 4bbl, dual 4bbl and 3 x 2bbl holley setups. A better carb for the Tbird is the
600 CFM square bore with vacuum secondaries. But a Holley 750 will work, You need to make sure you are running no higher then an 8.5 power valve. Also, you should drop your
primary main metering jets down to around a #71 or #70. In extreme cases like high altitude and the like, you might have to go as low as #68. But, every engine is an
individual. Some engines, depending on condition, may need a little more or less with respect to the main metering jet size. But, a power valve any lower then 6.5 will not
open soon enough and one higher in vacuum rating then 8.5 will open too often causing the car to drink gas and run too rich at part throttle. With the Holley carb, it is
critical that you have the float level set correctly before making any adjustments. It should be set with the engine running. You start the engine and then remove the screw
or sight plug that is on the side of each float bowl. Adjust the float level via the top screw and nut so that the fuel just starts to flow into the threads of the sight
plug hole. Tighten the adjusting nut and screw assembly and reinstall the sight plug and washer. Now, adjust the idle mixture screws in till the engine falters then back
them out about 1/2 turn. Next adjust the idle to around 550 - 600 rpm in gear. readjust the idle mixture screws with the car in gear. Now shut the engine off and remove
the carburetor. (I know this is a pain but there is a very important check you must make.) you will notice a tiny hole in each primary throttle bore near where the throttle
plates would contact the bore if they were allowed to close all the way. These are the idle fuel bleed holes. If you look in the same area around the throttle opening
(from the bottom) you should notice in one of the primary bores a vertical slot of about 1/64" wide by about 1/8", or a pair of holes with one above the other. With the
throttle plate at the idle position you set when running the engine, the throttle plate should be in the middle of this slot, or roughly between the two holes if your carb
has two holes. These holes, or the slot is your idle transfer port. The improper positioning of the throttle plate at idle relative to this port is the number one reason
for off idle bog and the inability to set idle mixture with the idle mixture screws on either side of the primary metering block. If your throttle plates are too far
closed, you have an air leak somewhere or the carb is just plain too big, or your secondaries are not closing all the way. You need to correct this problem. If it is too
far open, and exposes all the idle transfer port, ie, you can see all the idle transfer port under the primary throttle plates, then you need to either slightly adjust the
secondary plates open (you can only do this a little!) or you will need to drill two very tiny holes in the primary throttle plates. This condition is generally rare unless
you have a very VERY hot cam with a long duration and a bit of overlap. I doubt this would be the case unless you installed a cam that has the engine running at around 900+
rpm at idle and has a pretty good 'lope' to it.
Sooo what you want is to first disassemble the primary of the carb. Verify the power valve is either a 6.5 0r 8.5, install #71 jets, and reassemble it. Next plop it on
the car with at least two thick carb base gaskets so the large throttle plates will clear the heater/spacer, then start the engine and set the float level. next set the
idle as best you can at around 550 rpm in gear, now adjust the two idle mixture screws, again verify and or set the idle back to 550 rpm in gear, and finally remove the
carb and verify that the primary throttle plates are somewhere within the idle transfer slot area when at idle, or between the two idle transfer holes if the carb has holes
instead of a slot. If you do this right, the car will run quite well. You have two ways to verify the actual fuel mixture. One is to read the plugs the other is to use an
exhaust gas analyzer. One quick and dirty test is to leave the choke off. Start the car when cold and then let your foot off the gas. If it is set up right, and you let the
engine drop to the 550 rpm idle position when cold and with no choke, it should spit and sputter and stall. If it runs smooth when cold and without a choke, it is running
way too rich, and it will tend to load up and run rough once it gets hot or you are in traffic. If it is warm and wants to stall and spits and sputters like it is cold, you
have it setup too lean. When changing jets try not to go up or down any more then two sizes at a time. So if #70 are too rich, try #68.. etc. But, you may want to just try
the carb right out of the box. Heck if it runs perfect leave it alone. But with my freshly rebuilt 390, I had to drop down to #70 jets and use a 6.5 power valve to get the
thing to run lean enough. In stock form, the carb ran reasonably well, but was too rich. I mean 10 mpg on the highway and 7 mpg around town is not right, nor is a bit of
black soot on the rear bumper and thick black fluff inthe tail pipes correct.
Hope this helps.
Bill B.