High Idle

Hi everyone, 

So i finally got my Mustang running after 3 years of sitting and a partially rebuilt engine! I'm extremely happy and it sounds awesome! It took so long because this is my first time really tearing apart the top end of an engine and i'm still a novice when it comes to mechanics. But i'm very proud and thankful of everyone on this forum for helping me along the way. The only thing is that the car idles very high right now. I have an Edelbrock 650cfm carburetor on it and i'm pretty sure my linkage is all connected correctly. My guess is that it is the idle speed screw but i'm not sure. I'm sort of afraid to run the car with its high idle for more than 10-20 seconds because it hasn't ran in 3 years. How can I lower the idle speed?

Have you verified that your choke is fully disengaged? If it is, disconnect the kickdown and pop off the throttle cable. If it still won't drop down, you need to remove the carb off to figure out why it isn't completely closing the throttle plates.

As a side note, in your overhead shot, the angle of your throttle cable is excessive. It should be a straight shot at the pivot ball, not off at an angle, which is only going to get worse as the further the carb is opened.

Fast idle on the choke, you're not running it long enough for the choke to warm up and open, disengaging the fast idle. You can manually open the choke blades, blip the throttle and it should drop down to normal idle speed.

Fast idle on the choke, you're not running it long enough for the choke to warm up and open, disengaging the fast idle. You can manually open the choke blades, blip the throttle and it should drop down to normal idle speed.

Click to expand...

It's an electric choke that i haven't hooked up yet. It could be that, i didn't think i needed to hook that up to get the engine started so i'll do that next. Even though Edelbrock says to attach it to a 12v power source that isn't the ignition coil, is it okay to attach it to that for convenience sake?

Have you verified that your choke is fully disengaged? If it is, disconnect the kickdown and pop off the throttle cable. If it still won't drop down, you need to remove the carb off to figure out why it isn't completely closing the throttle plates.

As a side note, in your overhead shot, the angle of your throttle cable is excessive. It should be a straight shot at the pivot ball, not off at an angle, which is only going to get worse as the further the carb is opened.

Click to expand...

It's an electric choke that i haven't hooked up yet because i didn't need it to start the engine. I suppose i'll do that next.

Fast idle on the choke, you're not running it long enough for the choke to warm up and open, disengaging the fast idle. You can manually open the choke blades, blip the throttle and it should drop down to normal idle speed.

Click to expand...

It's an electric choke that i haven't hooked up yet. It could be that, i didn't think i needed to hook that up to get the engine started so i'll do that next. Even though Edelbrock says to attach it to a 12v power source that isn't the ignition coil, is it okay to attach it to that for convenience sake?

Click to expand...

Run a lead to the battery with an alligator clip for now, or loosen the choke cover and rotate it to the lean side just enough to disengage it completely.

You cannot run it to the coil, it will create an additional load on the resistor wire and reduce the voltage to the coil even further, as well as only getting a much reduced voltage to the choke, probably around 5 volts. I'll have to measure the resistance on an electric choke so I can calculate just how much reduction there is.

"partially rebuilt engine"

Does this includes a new cam or dist changed/removed?

If the above great tips improve but do not fix entirely and you did one of the two.

What about timing? A bit too much advance?

Vacuum: no leak?

If you rev by hand quickly and let go, does it return in the instant back to its initial rpm's?

I measured the electric choke resistance on a Holley, don't use Ebelbrocks anymore, two was enough.

Adding that to the voltage reduction from the resistor wire and the load from both the ignition coil and electric choke would reduce the voltage to the coil and choke to about 5.8 volts.