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Idle Adjustment
https://slantsix.org/forum/viewtopic.php?t=52814		 Page 1 of 3
Author:  crater [ Sun Jul 21, 2013 9:10 pm ]
Post subject:  Idle Adjustment
Can't seem to get the car to idle below 1k. I can adjust all the way out on the screw (Yes it is the correct screw), but it will be fully screwed out to where it will not longer be in contact with the plate that stops the throttle.

I also am wondering if the Idle is supposed to dip a bit when pressing the throttle?

Was thinking there may be a leak somewhere, but my vacuum gauge is showing 20 inches and is very stable, wont this usually bounce around if there is a vacuum leak?

Could it be the valve lash? (Which I'll be adjusting later this week after the new seals go on).

Heres a video of the tach and Vacuum gauge. Car is at temp from a nice drive around town. You can ignore that it is at 1200 and not 1,000 as I've noticed the spring is a bit worn on the throttle and isn't returning it properly. I'll be adjusting it as necessary tomorrow, it started raining on me as I took the video. If i go under the hood and push the throttle back it drops to 1k as expected.

http://www.youtube.com/watch?v=1jLe9FxVC5E
Author:  ILMopars [ Mon Jul 22, 2013 2:27 am ]
Post subject: 
Replace the spring first if you know it is worn out. Has the Carb been rebuilt? Did this start recently? What kind of Carb, make and number of barrels?
Author:  wjajr [ Mon Jul 22, 2013 5:16 am ]
Post subject: 
It could be throttle plate is hanging up in bore because throttle shaft bushings are too worn, or you have developed a vacuum leak somewhere; be it between carburetor base and manifold to head, and or any vacuum line and their related dashpots or diaphragms including power brake booster if equipped.

If you close the choke by hand does the idle settle down?
Spray carburetor cleaner around base of carb and all manifold connection points, dose idle rate change?
Test diaphragms of vacuum activated pull off devices.
Author:  crater [ Mon Jul 22, 2013 8:19 am ]
Post subject: 
Its a 1bbl Holley 1920. Has not been rebuilt recently as far as I know. Just acquired the car last week. Probably does need some TLC, but other than this it runs fine, throttle response is good. I'm driving the car around town right now, it starts and runs great outside the high idle.

Choke is working fine. The vacuum is pulling the cam as it warms up and switching to the curb idle screw, its just not lowering below 1k.

I'll take care of the spring after work today and look for vacuum leaks as suggested. I was under the impression that if there was a leak the vacuum gauge would bounce around. Is that not always true?
Author:  xjarhead [ Mon Jul 22, 2013 8:49 am ]
Post subject: 
Quote:
I was under the impression that if there was a leak the vacuum gauge would bounce around. Is that not always true?
Try reading this
http://www.secondchancegarage.com/public/186.cfm

Dave
Author:  wjajr [ Mon Jul 22, 2013 10:32 am ]
Post subject: 
One more thought:
Looking at your dash in youtube I assume your carburetor is operated via a throttle cable. Sometimes that cable can hang up due to being deformed or containing broken wire strands, and or it may not adjusted correctly with enough slack to allow throttle plate to come to rest on idle adjustment screw stop.
Author:  crater [ Mon Jul 22, 2013 10:56 am ]
Post subject: 
I'll check that as well. Thank you for the tips.
Author:  805moparkid [ Mon Jul 22, 2013 6:37 pm ]
Post subject: 
undo the 7/16 nut holding the throttle cable and see if it closes
Author:  crater [ Tue Jul 23, 2013 9:32 am ]
Post subject: 
I adjusted the spring to have some more tension and now it pulls all the way back, but the car is still not idling lower. The throttle i pulled back and it can't go further. Looks like it is prevented from going further by the rod that goes into the back side of the float I believe. Here is a video. at around 25 seconds you can see the part I'm talking about that goes into the carb. Sorry I'm not sure what that is so, still learning.

http://www.youtube.com/watch?v=h93GMH2CwMo


Didn't have time to try the spraying carb cleaner.

Only other thing I had time to check last night was the throttle cable and its not hanging up, there is slack when all the way out. Its definitely on the carb. Just not sure at this point if the carb is doing what it should, and the idle is high from a leak or something else as other have said. Will have to do some more poking around.
Author:  Reed [ Tue Jul 23, 2013 9:43 am ]
Post subject: 
OK. The rod you are referring to is the accelerator pump linkage. The plastic tab that disappears into the back of the float bowl is the accelerator pump. But that isn't your problem.

Your choke thermostat rod (the rod that runs from the exhaust manifold up to the choke valve at the top of your carb) is all bent to hell. It is supposed to be near perfectly straight. I will be stunned if your choke is working and adjusted properly. Your throttle linkage is hitting the bend in the choke thermostat arm and not closing all the way. That is why your idle won't go down. Your throttle isn't closing all the way.

Try this.

(1) Disconnect the choke thermostat rod from the choke and set it out of the way of any linkage pieces.

(2) Sart the car and see where it idles. If the idle drops, you have solved your problem. If the idle doesn't drop, try loosening the throttle cable nut and see if the throttle closes more.

Also, it sounds like you have either or both multiple exhaust leaks and/or misadjusted valves. Finally, are you sure your tachometer is set to read a six cylinder motor? That sure didn't sound like 1500-1700 RPM. Check the back of your tach for a switch with three positions: 4-6-8. Put it on 6.

See the carburetor operation and repair links for the 1920 given here: http://www.slantsix.org/forum/viewtopic.php?t=33102
Author:  crater [ Tue Jul 23, 2013 9:50 am ]
Post subject: 
Quote:
OK. Your choke thermostat rod (the rod that runs from the exhaust manifold up to the choke valve at the top of your carb) is all bent to hell. It is supposed to be near perfectly straight. I will be stunned if your choke is working and adjusted properly. Your throttle linkage is hitting the bend in the choke thermostat arm and not closing all the way. That is why your idle won't go down. Your throttle isn't closing all the way.

Try this.

(1) Disconnect the choke thermostat rod from the choke and set it out of the way of any linkage pieces.

(2) Sart the car and see where it idles. If the idle drops, you have solved your problem. If the idle doesn't drop, try loosening the throttle cable nut and see if the throttle closes more.

Also, it sounds like you have either or both multiple exhaust leaks and/or misadjusted valves. Finally, are you sure your tachometer is set to rear a six cylinder motor? That sure didn't sound like 1200 RPM.
The tach has the 3 way switch and it is set to 6 on that switch. Could there be something else causing it to not read properly from the ignition coil?

I'll try the rest of the stuff today when I get home. Will be doing valve seals and setting the lash this weekend.
Author:  Reed [ Tue Jul 23, 2013 9:52 am ]
Post subject: 
If the tach is set to 6, check your ground and where you have it connected to the ignition circuit. I believe that tach should connect directly to the (-) coil terminal.
Author:  crater [ Tue Jul 23, 2013 10:59 am ]
Post subject: 
Quote:
If the tach is set to 6, check your ground and where you have it connected to the ignition circuit. I believe that tach should connect directly to the (-) coil terminal.
Yeah its grounded to the body, but I'll try running a jumper to the - on the battery and see if that changes anything.

The wire is directly on the - of the coil. Power is attached a fused key ignition source and white for the dimmer is capped off for now.
Author:  Reed [ Tue Jul 23, 2013 11:18 am ]
Post subject: 
I could be completely wrong and you just have a quiet motor. Worry about the choke first.
Author:  DusterIdiot [ Tue Jul 23, 2013 12:18 pm ]
Post subject:  Lol...
Quote:
I could be completely wrong and you just have a quiet motor.
Reminds me of a true story when I was a little kid...
My grandma only drove Oldsmobiles, and only V-8's....her car needed to go to the shop for something. My Mom offered to give her a ride back home using the trusty '68 Valiant...(it's only 8 years old at this point...). My grandfather usually tuned up the Valiant and it ran very smooth all the time with not much of the "ticking" of the mechanical valve train under the hood. We pull up to a stop light and wait for the green to go. One minute into the wait, my grand mother leans over to my mom and says "Honey, I think the car died. You need to restart it." My mom knowing better (no oil idiot light showing), revs the engine and gets a small vroom and a little sewing machine noise from under the hood, replies to her "No, it's just a quiet running little 6 cylinder." Months later I heard my Grandma complain that the 330 under the hood of her Cutlass was way too noisy for such a nice car...




:lol:
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