arrghs--questions about idle speeds

[erik]

My apologies if these come off as really dumb questions but Im trying to adjust the idle mixture screws, timing, and set the idle rpm of my 76 Eldo.  My manual says curb idle should be 600rpm.  What exactly is curb idle?  For idle mixture, the book says 620 in drive (CA), for timing the idle should be set at 600 in park.

After I get everything hooked back up (vacuum advance tube, ALC tube, etc) the engine idles in park at around 875.  In drive, it idles around 550-75.  And it diesels like hell.

Also, should I set timing first and then set the idle mixture screws?  Or visa versa?

Finally, the manual says to open the idle mixture screws five turns and then screw them back until the rpms start to drop.  Ive got the things down to 1.5 turns from bottom and Im still not sure if thats where theyre supposed to be.  The engine seems to run okay but the car is hesitant when driving (I also set the timing to 6 BTDC).

Thanks so much.
Erik  

[Michael Stamps 19507]

I think your idle is too high as I set mine at around 600 in park.  I do that because normally I dont have a helper around to hold the brakes when its in drive.  

My 2 cents,
Stampie

[Bruce Reynolds # 18992]

Gday Eric,

QUOTE My manual says curb idle should be 600rpm. What exactly is curb idle?UNQUOTE

Now, To set the idle to a "curb" setting, firstly you have to be parked at the "curb" so that the footpath gives you a higher plain to stand on so you can reach the Idle Screw.   This method of setting was to enable short people to work on their cars without standing on a box.   Wooden boxes, these days are so hard to find and cardboard or foam ones just collapse.

Now that explanation is out of the way, the "curb" idle is mentioned as it is very hard to do the adjustment whilst running beside the car as it is idling down the street, and the driver cant see, because the hood is up.   This lead to many accidents.

Now, down to the serious part of the answer.

"Curb" idle is where the engine is idling, with the transmission selector in Neutral, the park brake applied, and all accessories that draw power turned off.

Next, when setting Ignition timing, the Vacuum advance hose to the distributor is to be removed, and plugged, so that there is no vacuum signal affecting the operation of the distributor advance mechanism.

Next, whatever the book said, it is correct, and if you follow the steps, you will be okay.

But, when you reconnect the vacuum to the Distributor, the distributor will immediately advance the timing to around 20 odd degrees, so setting it with the Vacuum off and plugged is a must, and 6 degrees is right.

But, the best setting will also depend on the condition of your Timing Chain, as if it is stretched, that will play with the cam to crankshaft position as well.   If it is stretched, then the cam will be physically retarded all the time, even when going in reverse.

I have found that the best way to time a motor, if you are unsure of the internals is to use the Vacuum Gauge method, whereby the highest reading is obtained.   Also advancing the timing till it Pings under accelleration, then back it off a couple of degrees until the pinking stops, works as well.

As far as the mixture screw adjustment goes, I usually start at 1 1/2 turns off seated, then work each one from there till it is idling nicely.   It will be necessary to do this adjustment a few times to get everything equalised, and optimum.

Takes a bit of juggling with dropping the idle speed as the engine revs rise as the mixture is adjusted, but, once the idling is set, at "Curb" idle, then the idle with the A/C turned on is adjusted at the A/C Fast Idle Solenoid, not the base idle, because that will affect the already set Curb Idle speed and idle speed in gear.

Hope this is clear it a bit.

Bruce,
The Tassie Devil(le),
60 CDV