Chasing an idle
Thread Starter
Drifting
Joined: Sep 2007
Posts: 1,572
Likes: 51
From: Wichita Kansas
[QUOTE=DUB;1593682758]It is worth a 'look-see'...because if the springs are to light...it can case for a problem when attempting to get to a curb idle.
I recently went through this on '67 427 tri-power. The supposed rebuilt distributor with electronic ignition actually had the wrong springs in it and it would not get down below
1200 rpm's and would die. When the original distributor was installed...it ran fine and a
curb idle could be set.
DUB[/QUOTE
Dub has me on track here
I recently went through this on '67 427 tri-power. The supposed rebuilt distributor with electronic ignition actually had the wrong springs in it and it would not get down below
1200 rpm's and would die. When the original distributor was installed...it ran fine and a
curb idle could be set.
DUB[/QUOTE
I honestly have no clue because in one of the past posts....when the temp dropped when the thermostat opened...the idle dropped and that makes no sense at all that temperature control rpm's...especially on an engine that is not computer controlled.
It often times is so hard to diagnose problems when 'we' are not there to see what is going on.
So...personally I would address the idle RPM issue and then see what goes on with the temp issue if that is even an issue after the idle has been corrected.
I am curious on how well it idles BEFORE the temp gets high enough to open the thermostat...because it should be able to achieve 'curb idle' BEFORE the temp reaches the point where the thermostat opens.
If the coolant temp is not to the point of boiling over (or overheating...which it appears it is not the case)...I am not taking any dynamics of the cooling system into consideration at this point.
DUB
It often times is so hard to diagnose problems when 'we' are not there to see what is going on.
So...personally I would address the idle RPM issue and then see what goes on with the temp issue if that is even an issue after the idle has been corrected.
I am curious on how well it idles BEFORE the temp gets high enough to open the thermostat...because it should be able to achieve 'curb idle' BEFORE the temp reaches the point where the thermostat opens.
If the coolant temp is not to the point of boiling over (or overheating...which it appears it is not the case)...I am not taking any dynamics of the cooling system into consideration at this point.
DUB
Last edited by Aggitated Monkey; Dec 19, 2016 at 06:10 PM.
Thread Starter
Drifting
Joined: Sep 2007
Posts: 1,572
Likes: 51
From: Wichita Kansas
Ok was trying to comment with a quote from Dub; but my phone app wouldn't let me. So read his input above.
I sgree this is an advance spring issue as mentioned. I will look into that however it has been below 10* here. So it will wait a bit.
For other thoughts on cooling system; it has nothing to do with the curb idle. I don't have a problem with the fans or shroud. All is in tact and all is new. The engine does not overheat and I have ran it in stop and go traffic when it's been 100*_105• with no problems. There is no sensor that controls anything.
When temp comes up to operating it holds the idle on its own. When temp is cool or cold and the chock comes off the high idle it needs a little gas feed to stay running until the temp comes up. I think this is very normal for any carb engine if the choke is not adjusted correctly or as suggested the advance springs are too weak.
Its not the trans cooler. The oversized cooler is more than adiquate. Not a part of the problem.
Plrsse re read what I first posted and re read what Dub provided above.
I think it's my solution. I also know that with a big cam fed on a carb it's never going to be perfect at low temps. I just like things perfect.
I sgree this is an advance spring issue as mentioned. I will look into that however it has been below 10* here. So it will wait a bit.
For other thoughts on cooling system; it has nothing to do with the curb idle. I don't have a problem with the fans or shroud. All is in tact and all is new. The engine does not overheat and I have ran it in stop and go traffic when it's been 100*_105• with no problems. There is no sensor that controls anything.
When temp comes up to operating it holds the idle on its own. When temp is cool or cold and the chock comes off the high idle it needs a little gas feed to stay running until the temp comes up. I think this is very normal for any carb engine if the choke is not adjusted correctly or as suggested the advance springs are too weak.
Its not the trans cooler. The oversized cooler is more than adiquate. Not a part of the problem.
Plrsse re read what I first posted and re read what Dub provided above.
I think it's my solution. I also know that with a big cam fed on a carb it's never going to be perfect at low temps. I just like things perfect.
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,754
From: Charlotte NC
When temp comes up to operating it holds the idle on its own. When temp is cool or cold and the chock comes off the high idle it needs a little gas feed to stay running until the temp comes up. I think this is very normal for any carb engine if the choke is not adjusted correctly or as suggested the advance springs are too weak.
I assume it is an electric choke???
Because if in a few more minutes of running...you do not need to 'feather' the gas pedal...then it just might be a bit touchy because it has not warmed up enough... or a very slight adjustment on the choke.
Due to you have a stouter cam...like I tell some customers with them. You can not expect it to be the same as a street cam. Sometimes they may require a bit more warm up period....and if the engine runs great when it has bit more time to get hot....then live with it. Like I tell them...me trying to get their engine to run PERFECTLY through the warm up stage ....when I am trying to get it 'just right' within a minute or two period of time when it is warming up is pointless....because that moment in time will soon no longer be an issue due to the engine is now hotter.
I worry about start up and fast idle...and how it runs when it is at operating temperature. Any temperature that falls between cold start up and operating temperature is pointless for me to spend time on.
DUB
Last edited by DUB; Dec 19, 2016 at 06:54 PM.
Thread Starter
Drifting
Joined: Sep 2007
Posts: 1,572
Likes: 51
From: Wichita Kansas
From what I am reading in this portion of what you wrote. IF the choke comes off a tab bit too soon ...and the coolant temp is still a bit low and it needs a little bit more fuel....THAT makes sense.
I assume it is an electric choke???
Because if in a few more minutes of running...you do not need to 'feather' the g
as pedal...then it just might be a bit touchy because it has not warmed up enough... or a very slight adjustment on the choke.
Due to you have a stouter cam...like I tell some customers with them. You can not expect it to be the same as a street cam. Sometimes they may require a bit more warm up period....and if the engine runs great when it has bit more time to get hot....then live with it. Like I tell them...me trying to get their engine to run PERFECTLY through the warm up stage ....when I am trying to get it 'just right' within a minute or two period of time when it is warming up is pointless....because that moment in time will soon no longer be an issue due to the engine is now hotter.
I worry about start up and fast idle...and how it runs when it is at operating temperature. Any temperature that falls between cold start up and operating temperature is pointless for me to spend time on.
DUB
I assume it is an electric choke???
Because if in a few more minutes of running...you do not need to 'feather' the g
as pedal...then it just might be a bit touchy because it has not warmed up enough... or a very slight adjustment on the choke.
Due to you have a stouter cam...like I tell some customers with them. You can not expect it to be the same as a street cam. Sometimes they may require a bit more warm up period....and if the engine runs great when it has bit more time to get hot....then live with it. Like I tell them...me trying to get their engine to run PERFECTLY through the warm up stage ....when I am trying to get it 'just right' within a minute or two period of time when it is warming up is pointless....because that moment in time will soon no longer be an issue due to the engine is now hotter.
I worry about start up and fast idle...and how it runs when it is at operating temperature. Any temperature that falls between cold start up and operating temperature is pointless for me to spend time on.
DUB
Race Director
Joined: Apr 2007
Posts: 11,152
Likes: 890
From: South Western Ontario
It has really been explained yet. You want to check the mechanical advance only and make sure the mechanical does not start to advance until an rpm above the idle rpm range in use. So, you probably want to make sure the mechanical doesn't move until above greater than about 1200rpm. Then, you want to plug-in the vacuum advance and make sure it is fully pulled at idle and doesn't move.
The best way to check the vacuum advance would be using a Mityvac and finding how much vacuum is required to fully move the advance. Then, use a gauge on the engine and make sure the engine vacuum is at least 2in-Hg more vacuum. without the right equipment, at least plug it in and make sure it stays fully advanced in and out of drive, even if you lower the idle below the normal idle rpm.
The reasoning is that idle rpm will somewhat follow the advance. So, if the advance drops as the rpm drops then that cause the rpm to drop even further. It's basically a feedback loop that works against having a stable rpm.
Many EFI systems will move the timing opposite of what the idle rpm is doing to try and stabilize the idle. So, if the idle rpm drops a bit the system will add some advance to correct the rpm.
The best way to check the vacuum advance would be using a Mityvac and finding how much vacuum is required to fully move the advance. Then, use a gauge on the engine and make sure the engine vacuum is at least 2in-Hg more vacuum. without the right equipment, at least plug it in and make sure it stays fully advanced in and out of drive, even if you lower the idle below the normal idle rpm.
The reasoning is that idle rpm will somewhat follow the advance. So, if the advance drops as the rpm drops then that cause the rpm to drop even further. It's basically a feedback loop that works against having a stable rpm.
Many EFI systems will move the timing opposite of what the idle rpm is doing to try and stabilize the idle. So, if the idle rpm drops a bit the system will add some advance to correct the rpm.
Last edited by lionelhutz; Dec 19, 2016 at 11:42 PM.
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,754
From: Charlotte NC
I did not mean to come across that you were 'picky'. Nothing wrong with trying to get it the way you want it. Sometimes what we may want may not be able to be achieved. It is just that if the engine seems to not be 'quite right' when it has not fully warmed up...then trying to get it to run correctly at that time of warm-up...in my opinion...is pointless. Because like I wrote...the engine is warming up and it will get warmer and warmer and then act as it should.
I worked on a big block that was finicky...once it got to correct operating temp....it would be able to peel your eye lids back. If it was not at correct temp...it...as I wrote...was finicky.
DUB
I worked on a big block that was finicky...once it got to correct operating temp....it would be able to peel your eye lids back. If it was not at correct temp...it...as I wrote...was finicky.
DUB
Last edited by DUB; Dec 20, 2016 at 06:23 PM.
