Originally Posted by midias
How did you adjust your idle settings? Did you use a vacuum gauge? Air/ Fuel Meter?
Does the car have a cat?
I just set it by ear and road testing. You can use your tach and a vacuum gauge if you want to.
CAT should not matter, unless it is plugged and causing a restriction. It would only be a problem at WOT, not idle.
What is your calculated static compression ratio?
OK. Here is what you have to do. That XE274 is big enough for you have reduced manifold vacuum. 11" Hg @ 800 RPM & 14" Hg @ 1000 RPM w/ no load.
Are you you using a PCV valve with a breather in the opposite valve cover? You should be. PCV is a controlled vacuum leak, and will effect your idle.
What does your distributor advance curve look like?
Take the carb off and turn upside down. Set the idle speed screw for "squares" on the transition slots. Now back it off and count the # of turns it took, so that when it is back on the engine, you now know how many turns it takes to get back to that setting. Set it back to squares.
The following assumes that your distributor, carb, etc. are properly working and have no issues.
Set the mixture screws equally at a good starting point.
Disconnect and plug the vacuum advance. BTW, when you have it connected, it connects to PORTED. Start the car and try to set the initial timing to about 20*. It has to be done at a low enough rpm that the centrifugal advance is not kicking in. Don't have it advanced so far that the engine is hard to crank or kicks back. But you want enough that you can idle, even if the rpm is a little high, or low. You are trying to give the engine what IT wants.
Now everything should be in the ballpark, and you can begin to fine-tune it.
Because of that cam, your engine requires more air at idle. If you use the idle speed screw to raise the idle, you are also going right past the idle and transition circuits, into the main jet circuits. This is where some people's engines have that running rich at high idle, fouling plugs, burning eyes, etc. condition. Smaller main jets are NOT the answer here! You need more AIR - not fuel. How can you do that? Ever heard about drilling holes in the throttle plates? But if you do that, once you go too far, you can't go back. I'm going to explain how to achieve the same thing without doing that.
Your engine should require no more than a .250” vacuum leak hole. This would be equivalent to (2) .177” holes in each primary throttle plate, or (4) .125” holes if there was 1 hole in each plate (PRI & SEC).
So find a plug or port on the intake manifold or carb that would open up a 1/4" hole. YES, creating a vacuum leak, but allowing the engine to get more air WITHOUT going through the carb. GET IT? RPM increased, right? Now you can further retard your initial timing and fine tune your mixture screws. Try to leave the IDLE SPEED screw alone. If you must touch it, only deviate from the squares setting by maybe 3/4 of a turn in either direction. Keep going back and forth between the timing and the mixture screws.
You can make this "leak" adjustable by installing one of these: (attached), or something similar. Just be sure to keep it clean. If you install it into your air cleaner base (inside the filter area), and run a rubber vacuum line to it, the air filter will keep it clean.
You can read this also: http://www.hotrodgenius.com/html/carburetion1.html