I recently installed a LD4B intake and a rebuilt Holley 4160 on my stock 71 318. I’m trying to get my rpm down at idle, but my curb idle screw seems to have no affect. Any suggestions on how to fix it? As of last night it was idling at about 2400 in park.
If the engine was running fine before the intake,carb went on; and
If you did not take the Distributor out,or
you did not change the timing, And
the float level is right and stable;and
your 4160 is a vacuum-secondary carb
then go to "A"
But if you have monkeyed with the timing, disconnect the Vcan, plug the port, then reset the timing to 5*BTDC. And now continue at A)
A) make sure the vcan is connected to the SPARKPORT . Pull off the hose, and check the port for vacuum.
If you have vacuum at the SPARKPORT, then the primary throttle-blades are indeed too far open. Way too far.
I can think of at least three reasons why this could be;
1) the base-gasket you used is hanging them open
2) the throttle blades themselves are not properly centered in the shaft.
3) the choke fast-idle cam is engaged
But if there is no vacuum at the sparkport; then the primary throttle butterflies are NOT way too far open. They could still be somewhat too far open, but IMO, the problem is elsewhere. I can think of only three reasons now for the high idle;
a) the secondaries are hung open;make sure the Vacuum pod has sufficient spring in it and the diaphragm is supple and and PROPERLY INSTALLED (see note 1) or the secondary throttle blades are not centered in the shaft, or the secondary cracking screw is too far in.
b) one or both of the brake booster, or the PCV port, is open,
c) the intake is sucking air, but I doubt this, at this point. If this was the case with the primaries closed, the engine would be too lean to run.
now, if you can't get it to work from the above,
here is how it should be;
Take the carb off and empty it
With the speed screw backed right off AND the fast-idle cam NOT ENGAGED;
ALL throttle blades should be fully closed. Shine a flashlight in from the top while you are looking at the bottom, and you should see as close to zero lite as possible where they touch the bores at 90* to the shafts. If the secondaries are hung open, go look for the cracking screw, and fix it. They should be closed up tight but not sticking.If the cracking screw does not work; Go find the linkrod from the Vacuum pod, and make sure it is pushing the secondaries closed.
Now; with the fast idle cam NOT engaged, turn in your speedscrew until the butterflies just start to move, then add two more turns. Flip the carb upside down, keeping the fast-idle cam still NOT engaged. Go find the transfer slots at the very front of the bores; they are the only vertical slots there. With the butterflies still closed, adjust the speed screw until the look like perfect squares on the engine-side of the blades. Now; do not move them again ever, until some one tells you to. From now on you will be using IDLE-timing to set the idle-speed. Ok , reset the mixture screws to 3/4 turn out. Recheck the secondaries are still closed.
Next, go find the PCV and brake-booster ports. You must use the PCV port on the front, on the baseplate near the center. The big port at the back, if you have one, is for powerbrakes. If you do nor have PB then that port has to be plugged in such a way that it cannot fall off or be blown off during a backfire in the intake
Next; go get your base gasket and make sure it fits properly and that it is impossible for the butterflies to hang up on it. If you have a carb base insulator, make sure it seals. Make sure all unused ports on the intake, and the carb,are plugged.
Ok all set; reinstall the carb. Pour ~50cc of gas thru the primary bowl vent into the bowl, and hit the key.
At 5* idle timing, the hot idle should be around 500/550 in Park.
Lets see how it goes.
If the engine will not stay running DO NOT change the speed screw! Instead just give the D a tug until it does, and let her warm up. During the warm-up, it does not matter if the timing is "not right".
But if the idle is still way too high; check your float levels. If good, the only way this can happen is if the engine is getting air WITH fuel from somewhere other than the low-speed circuit. So;
simultaneously stick a finger over each front booster, to make sure they are not flowing. If good IDK, maybe the PV is ruptured. Maybe a wrong metering block gasket was installed.IDK. Maybe someone else will chime in.
Note 1
When you install the diaphragm, before you put the cover on, you have to "Preload" it, which is simple grabbing the linkrod and immobilizing it for the duration of the cover install. After the cover is installed and tightened, then you can release the linkrod and install the assembly with it's gasket, onto the carb.
note 2
Ballparking the timing without a timing light;
Follow the #1 sparkplug wire to the cap, and locate the corresponding tower. With a Sharpie, mark the aluminum body, on the tower centerline. Pop the cap off. Find the rotor tip. By cranking the engine over by hand, align the rotor-tip to your mark. Next go find and clean your timing tab. Also locate the Index line on the balancer. Crank the engine by hand backwards until the index line aligns with the 10* advance mark on the tab. That would be the 10 on the CCW side, from the front, of 0(zero).
Now back to the Distributor.
Remove the coil wire from the cap and set it on a grounded-to-the-battery surface, so it has to spark to get there, and so you can either see it or hear it.
Find your reluctor, the thingy with the 8 vanes sticking off it. One of those vanes should be very close to the center "pole-piece", of the pick-up, which itself is centered in the surrounding magnet. Got it? Loosen the hold-down screw under the D just enough so you can rotate it. Push the vacuum pot on the side of the D back towards the firewall, a half a vane, just a few degrees. Now go turn the Ignition key to RUN, just RUN, and only to RUN. Back under the hood; listen and watch for spark, as you now PULL on the vacuum pot until the vane lines up with the pole-piece, or slightly past. Did you hear or see the spark. Turn off the shop radio. Do it again; first back up the pot a half a vane then repeat. Repeat as often as necessary until you have repeatable results; then tighten the hold down clamp, and turn off the key.. Your idle-timing is now ball-parked very close to 10* BTDC, and is ready to idle, and drive, just DO NOT open the secondaries until you get a timing light and are able to set your power-timing.
Ok I think that's about it.
Some of these things have already been mentioned by others, but now you have it all in one post. If anyone spots a fubar on my part, or wants to add something, hey, I'm not perfect lemmee know and I can add it.
Happy hunting.
