| What is you idle rpm ? [message #248570] |
Sun, 27 April 2014 19:43  |
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Loffen
Messages: 1087
Registered: August 2013
Location: Norway
Karma: 1
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Just did a tuneup on DT and are not happy with the Idle.
I did use an OTC 4 gas for the adjustment and took it by the book, 600 rpm in drive, under 0.2 in CO, just did dail it at 14.7 A/F and got just around 2 in CO2 and 0.1 CO give or take a little
Anyways out if drive the idle was close to 1000 Rpm, took it down to 525 Rpm in drive and got about 800 Rpm in park, no problem with the servo in drive but still a little high in park for my taste in park.
So what is your Rpm at idle in park and drive, and if you know what is your high idle Rpm (Choke in drive)
1973 23' # 1848 Sky Blue Glacier called Baby Blue and a 1973 26'-3 # 1460 Parrot green Seqouia Known as the Big Green,
And sold my 1973 26'-2 # 581 White Canyon lands under the name Dobbelt trøbbel
in Norway
[Updated on: Sun, 27 April 2014 19:50] Report message to a moderator |
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| Re: What is you idle rpm ? [message #248571 is a reply to message #248570] |
Sun, 27 April 2014 20:09  |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| Loffen wrote on Sun, 27 April 2014 20:43 |
Just did a tuneup on DT and are not happy with the Idle.
I did use an OTC 4 gas for the adjustment and took it by the book, 600 rpm in drive, under 0.2 in CO, just did dail it at 14.7 A/F and got just around 2 in CO2 and 0.1 CO give or take a little
Anyways out if drive the idle was close to 1000 Rpm, took it down to 525 Rpm in drive and got about 800 Rpm in park, no problem with the servo in drive but still a little high in park for my taste in park.
So what is your Rpm at idle in park and drive, and if you know what is your high idle Rpm (Choke in drive)
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I don't own any fancy instruments at all anymore, I just set things so they "feel right".
A shirt sleeve (20°C) start will run up to about 13~1400. I don't let it stay there very long.
Kick it off the high idle cam it will drop to ~850 cold (Park)and drop to 600~650 when put in drive.
When fully warmed up, she will hang a 650~700 and only drop to 600 when put in drive.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: What is you idle rpm ? [message #248572 is a reply to message #248570] |
Sun, 27 April 2014 20:16 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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| Loffen wrote on Sun, 27 April 2014 18:43 |
Just did a tuneup on DT and are not happy with the Idle.
I did use an OTC 4 gas for the adjustment and took it by the book, 600 rpm in drive, under 0.2 in CO, just did dail it at 14.7 A/F and got just around 2 in CO2 and 0.1 CO give or take a little
Anyways out if drive the idle was close to 1000 Rpm, took it down to 525 Rpm in drive and got about 800 Rpm in park, no problem with the servo in drive but still a little high in park for my taste in park.
So what is your Rpm at idle in park and drive, and if you know what is your high idle Rpm (Choke in drive)
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My 403 is very happy at 900 RPM in neutral after the fast idle is off. I run my fast idle at about 2000 rpm so I can charge my batteries after sitting. The fast idle will stay on the fast idle cam even after the choke comes off as long as you don't move the throttle.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] What is you idle rpm ? [message #248576 is a reply to message #248570] |
Sun, 27 April 2014 20:24 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Espen,
Ref: MM X-7525 / Section 6M - Engine Fuel System / Pages 6M-21 to 6M-25
These pages provide detailed instructions on how to set all the adjustments on the carb.
Regards,
Rob M.
-----Original Message-----
From: Espen Heitmann
Just did a tuneup on DT and are not happy with the Idle.
I did use an OTC 4 gas for the adjustment and took it by the book, 600 rpm in drive, under 0.2 in CO, just did dail it at 14.7 A/F
and got just around 2 in CO2 and 0.1 CO give or take a little
Anyways out if drive the idle was close to 1000 Rpm, took it down to 525 Rpm in drive and got about 800 Rpm in park, no problem
with the servo in drive but still a little high in park for my taste.
So what is your Rpm at idle in park and drive, and if you know what is your high idle Rpm (Choke in drive)
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] What is you idle rpm ? [message #248581 is a reply to message #248576] |
Sun, 27 April 2014 20:37 |
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Loffen
Messages: 1087
Registered: August 2013
Location: Norway
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Yes Rob I know, done by the book 
Well that will say almost by the book, take a look at page 6M-24 (figure 30), do you see a pretty large difference between the two ways to adjust the CO ?
This will for sure give a large difference in Rpm at idle.
1973 23' # 1848 Sky Blue Glacier called Baby Blue and a 1973 26'-3 # 1460 Parrot green Seqouia Known as the Big Green,
And sold my 1973 26'-2 # 581 White Canyon lands under the name Dobbelt trøbbel
in Norway
[Updated on: Sun, 27 April 2014 20:38] Report message to a moderator |
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| Re: [GMCnet] What is you idle rpm ? [message #248585 is a reply to message #248584] |
Sun, 27 April 2014 20:46 |
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Loffen
Messages: 1087
Registered: August 2013
Location: Norway
Karma: 1
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Bob what is your Rpm in drive ?
1973 23' # 1848 Sky Blue Glacier called Baby Blue and a 1973 26'-3 # 1460 Parrot green Seqouia Known as the Big Green,
And sold my 1973 26'-2 # 581 White Canyon lands under the name Dobbelt trøbbel
in Norway
[Updated on: Sun, 27 April 2014 20:48] Report message to a moderator |
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| Re: [GMCnet] What is you idle rpm ? [message #248588 is a reply to message #248585] |
Sun, 27 April 2014 21:04 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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| Loffen wrote on Sun, 27 April 2014 19:46 |
Bob what is your Rpm in drive ?
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I really don't know. I set the idle based on how hard the transmission engages and if I have a hesitation in drive. I've noticed that a low idle gives just a very slight hesitation when I launch. I usually set the mixture screws in drive. I don't need to pass any emission tests so i go back and forth between neutral and drive untill I feel the best sweet spot. Since I live in Arizona, all my adjustments are with the AC running.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: What is you idle rpm ? [message #248594 is a reply to message #248570] |
Sun, 27 April 2014 21:36 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
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If you are lean then there will be a bigger difference between neutral and drive. I don't follow your park scrnario as park is neutral but with the park pawl engaged. I go for max idle RPM via mixture and then to the lean edge of that with only a slight RPM drop. Most GM vehicles of mid 70s were 25 RPM lean drop per mix screw but don't kmow about the GMC.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: What is you idle rpm ? [message #248668 is a reply to message #248594] |
Mon, 28 April 2014 12:12 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
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| JohnL455 wrote on Sun, 27 April 2014 20:36 |
If you are lean then there will be a bigger difference between neutral and drive. I don't follow your park scrnario as park is neutral but with the park pawl engaged. I go for max idle RPM via mixture and then to the lean edge of that with only a slight RPM drop. Most GM vehicles of mid 70s were 25 RPM lean drop per mix screw but don't kmow about the GMC.
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You're right on the lean drop but I always ignored that and set for a hair rich.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: What is you idle rpm ? [message #248670 is a reply to message #248617] |
Mon, 28 April 2014 12:19 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
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To me the idle in drive is the most important one. I usually set it for a nice smooth stable feel and then see what it is in neutral and also make sure that when I shift into drive, that it doesn't slam into gear.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: What is you idle rpm ? [message #248687 is a reply to message #248685] |
Mon, 28 April 2014 16:30 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
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| bwevers wrote on Mon, 28 April 2014 14:58 |
Just a few suggestions:
If you see a large difference in RPM, I would
check to see if the ported vacuum advance is working.
Or if the TVS valve is stuck. This valve speeds up the
engine when cold. It switches to ported vacuum when warm.
Try disconnecting the vacuum hose to the distributor and
plug the hose. Then check to see if you get the large RPM change.
You might also have the vacuum hoses in the wrong place.
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I don't think that is the way our GMC's are plumbed. We have no EGR in the system. Our TVS uses ported vacuum when cold and at normal operating temperature and switches to manifold vacuum when hot. On manifold vacumm, the RPM's speed up considerably due to more advanced timing.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: What is you idle rpm ? [message #248689 is a reply to message #248570] |
Mon, 28 April 2014 16:46 |
xplorid
Messages: 213
Registered: February 2012
Location: Boise
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Bob - regarding switch to manifold vacuum when hot - does that mean above some temp threshold it is expected that idle rpm will increase significantly? What is the approx increase in rpms? What is the temp threshold?
Is this a probable explanation for my fast idle after the coach has been driven for a while?
Thanks.
1974/94 GMCII by Explorer
Manny 6.5 TD Al radiator
1 ton front 4 bags back
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| Re: What is you idle rpm ? [message #248692 is a reply to message #248689] |
Mon, 28 April 2014 16:52 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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| xplorid wrote on Mon, 28 April 2014 15:46 |
Bob - regarding switch to manifold vacuum when hot - does that mean above some temp threshold it is expected that idle rpm will increase significantly? What is the approx increase in rpms? What is the temp threshold?
Is this a probable explanation for my fast idle after the coach has been driven for a while?
Thanks.
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I don't have the manual handy here at work but it is probably around 210 or so. I run mine on manifold vacuum all the time and I can say the RPM difference is at least 500 or more. I suspect many folks (who still have a TVS) are in that mode of operation a lot of time if their engines tend to run a bit hot.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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