cant get the idle down after timing
Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,775
Likes: 4
cant get the idle down after timing
i just timed my 69, and im having trouble getting the idle back down.
when i started, i was idling at ~500rpm with 3*BTDC. i took it up to 13.5* BTDC to get me to 36* max at 3000rpm. its actually a tad high, and i may drop it back down to 12*, but its running great and not knocking where its at right now.
anyhow, im currently sitting at 725-750 and cant get it any lower, and the screw is backed all the way out. i want to get it back to 500.
when i started, i was idling at ~500rpm with 3*BTDC. i took it up to 13.5* BTDC to get me to 36* max at 3000rpm. its actually a tad high, and i may drop it back down to 12*, but its running great and not knocking where its at right now.
anyhow, im currently sitting at 725-750 and cant get it any lower, and the screw is backed all the way out. i want to get it back to 500.
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
If it's the factory tach, who knows how many rpm the engine is actually turning when the tach reads 500. If the OP is comfortable with his idle at an indicated 500, it may actually be turning 700 in reality. Anyway, even if the tach is inaccurate, his idle is still higher than he would like, and he can't seem to get it down. He has run out of adjustment on his idle speed screw, apparently. There should be enough adjustment on the idle speed screw that you can adjust it so low that the engine will not idle at all, so something is wrong here. Could be a small vacuum leak somewhere, unmetered air entering the system.
Scott
Scott
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Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,775
Likes: 4
all right, im back.
ive ran it at about 500 rpm for some years now, and itll idle that low all day. so id like to keep it there. and surprisingly, my tach is right on the money. ive got a digital inductive timing light, and whatever it says on the timing light, its exactly where the tach is pointing to.
the dizzy springs and weights are still the same
the vac line was disconnected and plugged before timing
and theres no extra play in the throttle linkage, so its being pulled back to its maximum amount.
the choke is disconnected and wired open.
ive sprayed the carb pretty well with wd40, and im not finding any vacuum leaks.
i probably should also mention that im running a holley DP, and not the stock quadrajet.
ive ran it at about 500 rpm for some years now, and itll idle that low all day. so id like to keep it there. and surprisingly, my tach is right on the money. ive got a digital inductive timing light, and whatever it says on the timing light, its exactly where the tach is pointing to.
the dizzy springs and weights are still the same
the vac line was disconnected and plugged before timing
and theres no extra play in the throttle linkage, so its being pulled back to its maximum amount.
the choke is disconnected and wired open.
ive sprayed the carb pretty well with wd40, and im not finding any vacuum leaks.
i probably should also mention that im running a holley DP, and not the stock quadrajet.
Burning Brakes
Joined: Apr 2013
Posts: 926
Likes: 2
From: Castle Rock CO
From old experience with early engines I going to throw a few ideas out there. First off I love the lope of an old engine at 500 RPMs with solid lifters and many automatics suggest setting the idle at this speed in gear. 750 RPMs out of gear and between 500 to 600 RPMs in gear on an automatic Tranny.
You may want to replace the Vacuum Advance Module on the Carb if the diaphragm is worn out it will not advance correctly or not allow the engine to idle properly because it is advancing the timing for you at the wrong time than not allowing you to set it properly.
Replace the entire Distributor unit if it is causing problems with timing and Dwell. I had to do this on a 1976 HEI System many years ago on a Chevelle because it was worn out and would wobble and not provide me with consistent timing on the Light. It would jump around a few degrees.
Do you own a Vacuum Gauge? If not purchase one and check the carb for leaks. There certain pressures to be expected on the vacuum system. The Idle will run high if too much air is in the system and cause it to not adjustable.
Just a few thoughts from my past experiences to get a low constant idle speed.
You may want to replace the Vacuum Advance Module on the Carb if the diaphragm is worn out it will not advance correctly or not allow the engine to idle properly because it is advancing the timing for you at the wrong time than not allowing you to set it properly.
Replace the entire Distributor unit if it is causing problems with timing and Dwell. I had to do this on a 1976 HEI System many years ago on a Chevelle because it was worn out and would wobble and not provide me with consistent timing on the Light. It would jump around a few degrees.
Do you own a Vacuum Gauge? If not purchase one and check the carb for leaks. There certain pressures to be expected on the vacuum system. The Idle will run high if too much air is in the system and cause it to not adjustable.
Just a few thoughts from my past experiences to get a low constant idle speed.
Last edited by MakoJoe; Sep 14, 2013 at 10:42 PM.
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
all right, im back.
ive ran it at about 500 rpm for some years now, and itll idle that low all day. so id like to keep it there. and surprisingly, my tach is right on the money. ive got a digital inductive timing light, and whatever it says on the timing light, its exactly where the tach is pointing to.
the dizzy springs and weights are still the same
the vac line was disconnected and plugged before timing
and theres no extra play in the throttle linkage, so its being pulled back to its maximum amount.
the choke is disconnected and wired open.
ive sprayed the carb pretty well with wd40, and im not finding any vacuum leaks.
i probably should also mention that im running a holley DP, and not the stock quadrajet.
ive ran it at about 500 rpm for some years now, and itll idle that low all day. so id like to keep it there. and surprisingly, my tach is right on the money. ive got a digital inductive timing light, and whatever it says on the timing light, its exactly where the tach is pointing to.
the dizzy springs and weights are still the same
the vac line was disconnected and plugged before timing
and theres no extra play in the throttle linkage, so its being pulled back to its maximum amount.
the choke is disconnected and wired open.
ive sprayed the carb pretty well with wd40, and im not finding any vacuum leaks.
i probably should also mention that im running a holley DP, and not the stock quadrajet.
Anyway, let's take a look at what is going on here, and try to think about it logically. The front throttle blades are all the way closed, and it idles high, right? The first place I would look, after verifying that there are no vacuum leaks, is the secondary throttle blades. If they are too far open at idle, they will allow too much air in, acting sort of like a vacuum leak. Not a true vacuum leak, but it will mimic the symptoms, sort of. It's impossible to say if this is the problem or not, it's just something to check. It may also be worth the time and effort to remove the carb, and set the primary throttle blades so that .020" of the transition slot is showing beneath it, and use the secondary adjustment to set idle once the carb is back on the car.
Scott
Le Mans Master
Joined: Nov 2006
Posts: 7,215
Likes: 1
From: Orlando FL
or something is stopping the primary from closing all the wayGood luck and keep looking..maybe get a second set of eyes
Race Director
Joined: Feb 2001
Posts: 11,301
Likes: 2,096
From: Grapevine Tx
2018 C3 of Year Finalist
2016 C3 of the Year Finalist
If your double pumper has that small set screw that cracks open the back barrels, it could bet set wrong. Back it out some. It's upside down on the right side of the carb (on mine, not a double pumper).
Race Director
Joined: Apr 2000
Posts: 17,676
Likes: 201
From: Who says "Nothing is impossible" ? I've been doing nothing for years.
IMHO 500rpm is way too low. 750-800rpm is good. At night with the headlights on, stereo etc. do they go dimmer when stopped at the lights. I would be very surprised if they didn't.
Are you trying to get a racecar lope at the lights ? Your alternator would not be charging anything at that RPM unless you have an overdrive pulley on the alternator which is no good for high rpms
Are you trying to get a racecar lope at the lights ? Your alternator would not be charging anything at that RPM unless you have an overdrive pulley on the alternator which is no good for high rpms
Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,775
Likes: 4
im not gonna lie, im trying to get that lope back. and after driving it for so long at 500, the 7-750 just seems way to high.
and the alternator is charging everything just fine at that idle. i dropped a CS144 in there, and i can have my stereo cranked (650wrms) and the headlights on with the brights, and theres no dimming at all.
getting back to the actual problem, ill start going over things tomorrow. its been crappy and rainy all day, so i havnt done anything with the car today.
and the alternator is charging everything just fine at that idle. i dropped a CS144 in there, and i can have my stereo cranked (650wrms) and the headlights on with the brights, and theres no dimming at all.
getting back to the actual problem, ill start going over things tomorrow. its been crappy and rainy all day, so i havnt done anything with the car today.
Thread Starter
Safety Car
Joined: Jun 2005
Posts: 3,775
Likes: 4
im thinking i found my problem. looks like my carb has started leaking from a couple of areas. i know the guy i use to rebuild my carbs said, figure theyll need a rebuild every 3-5 years. the ethanol crap just destroys the gaskets and gums up the carb.
weeping from the screw in the bowl
small pool under the fast idle. that formed when i was pumping some gas through the carb when the car wasnt running.
primary butterfly shaft appears to be leaking
secondary bowl appears to be weeping a bit again. ive had problems with this one for years now.
weeping from the screw in the bowl
small pool under the fast idle. that formed when i was pumping some gas through the carb when the car wasnt running.
primary butterfly shaft appears to be leaking
secondary bowl appears to be weeping a bit again. ive had problems with this one for years now.
Burning Brakes
Joined: Sep 2009
Posts: 1,124
Likes: 140
From: Western New York
I've heard that if your idle stays up too high for more than 4 hours, you should go to the hospital!
Seriously, though, it looks like it's time for a carb rebuild or even a new carb.
Duane
Seriously, though, it looks like it's time for a carb rebuild or even a new carb.
Duane
