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Need Correct Engine Idle Speed
According to my Reference (Chilton Mustang 1965-73, Page 26), the Idle Speed for a stock 351CJ with manual transmission would depend on the Distributor.

If the Distributor is dual diaphragm the Idle Speed is 1000. If it has a single diaphragm, the Idle Speed is 500.

For the same application (351CJ) with Automatics, the Idle Speed would be 800/500, respectively.


Do the RIGHT thing.
Thanks BT... 1000 seems to be the sweet spot.

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73StangCoupe;79267 Wrote:My thanks go to all that replied. I know this is a very simple thing, it's also pretty important. This forum and the folks that are always there to answer any question, are such an valuable resource when it comes to keeping these beauties going down the road. You all do it with such ease, I'm not sure you actually realize how helpful you all really are. Anyway, I had it set at 800 RPM but when I put the A/C on, it almost stalled out. I have it back up to 1000 RPM, that seems to be where it should be, especially with the A/C on. Thanks again.

I too am very impressed with the level of commitment by the folks on this forum. I posed a very simple (yet confounding) post regarding wiring and WolverineAngel was stead fast in helping me to get over my speed bump. I belong to Stangfix as well and truly enjoy the wisdom, camaraderie, and off topic conversations, however I always felt like the "redheaded stepchild" until Midlifegoodjob suggested this forum. Quite honestly: I look at my 73 vert in a whole new (positive) light since reading all the posts out here.
I was a Ford service line technician in the early seventies. Upon completion of a V8 points, plugs, condensor minor tune-up this was the engine adjustment procedure:

Dwell - 30 degrees, +/- 1 degree (make sure you lube the cam that the points ride on)

Timing - set at recommended factory setting for that engine with the vacuum line(s) off and plugged at the distributer. The Timing should be set with engine at about 650 rpm, curb idle, idle solenoid unplugged.

Carb adjustment - Reconnect vacummn line(s) to distributer, leave curb idle at 650 rpm, idle solenoid still unplugged. If using a manifold vacuum guage, adjust carb mixture screws to achieve highest manifold vacuum reading on the gauge (around 29 inches) and try to keep mixture screws within a 1/2 turn of each other.

Without a vacuum gauge, use a dwell tach. Screw in mixture screws to lean engine short of the idle starting to stumble. At that point you can back out the mixture screw a 1/2 turn if you want to avoid a stumble on acceleration. The mixture screws should be within a 1/2 turn of each other from the closed position. Now verify your curb idle is 650 rpm. If so, now connect the idle solenoid and set this idle at 750 to 825 rpm. On most Ford vehicles the idle solenoid is energized with the ignition. However, some were energized when the A/C compressor was on. If this is the case the idle was still set at 750 to 825 rpm. Get in the vehicle, hold the brake and put the vehicle in gear. If the overall vehicle idle remains above 650 rpm with the A/C on, you are fine. Otherwise, adjust the idle solenoid to achieve optimal idle. The purpose of the idle solenoid was to allow the throttle to drop down to a lower position on the carb to reduce the incidence of "dieseling" caused by shutting off an engine at a high idle while burning high octane fuel.

Another check on the carb is the accelerator pump lever. Make sure the clearance on the eccentric cam is minmal and that the cam is lubed with a small amount of light grease. This will also help prevent a stumble or hesitation when accelerating from a dead stop.

The automatic choke fast idle for the highest point of the cam was usually set at 1200 to 1400 rpms. The choke spring housing is normally set at the midpoint between lean/rich.

Do a final inspection of all vacuum lines to avoid leaving a leak to the manifold. Test drive the vehicle and tweak these settings to your final satisfaction.

In the seventies this was done roughly every 12,000 to 15,000 miles.

A major tune-up included plug wire replacement, carb overhaul and compression testing of each cylinder. This was done at about 50,000 miles.
Iowa... You hit the nail on the head. The guys on this forum are the absolute best. All are welcome are the help you get is unbelievable.

Thanks Jeff.... I'll have to print that post out!

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Midlife did a good job? That low-down good-for-nothing....*G*
What car and what engine? Newer engines are different and make different noises. The idle on newer cars are controlled by the computer, which sets the idle speed based on numerous parameters, including engine temperature, oxygen readings in the exhaust, air intake temperature, and so on.

If your engine has variable valve timing the knocking sounds may be coming from the valve timing mechanism, may be normal, or not.

This forum is for 1971, 1972, and 1973 Mustang owners, much different than how a 2006 operates.

If you are interested in our cars please go to the introduction page and introduce yourself and your car.

I would recommend you find a forum that is more specific to your brand and year of car.

“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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