Home » Public Forums » GMCnet » Tune and timing B4 the Big Trip
| Tune and timing B4 the Big Trip [message #214424] |
Mon, 15 July 2013 08:55  |
xplorid
Messages: 213
Registered: February 2012
Location: Boise
Karma: 0
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Senior Member |
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About set to leave on our 1st RV trip ID-NY and back, I want to tune the 455. I have a timing light, tach meter, a new vacuum gauge, and very little experience on this vehicle. I have read all the past posts I could. They seem to say (with a Patterson distributor on a '76 engine) -
plug the vacuum line to the distributor
set idle at 1100 or set idle at 550-600 (different posts)
aim for 12 deg initial timing with this distributor
reconnect vacuum, start engine, and set idle
adjust the 2 mixture screws on the distributor 1 at a time to max vacuum
reset idle if necessary
drive it and adjust from there, with pinging under load as the guideline for further timing adjustments.
Something like that. So here's my thing: I drove from Florida to here last year after purchase, and other than some vapor lock it ran well enough, 9+mpg, and about a quart of oil every 800 miles.
Last fall the distributor failed because of an improperly mounted cap and rotor so I bought the Springfield Ignition thru Applied. A GMC buddy here (another Jim) plopped the new distributor in and dialed it quickly saying "that sounds about right". Ran great and I did not think about again until this weekend, prepping for the big trip.
So, I hooked up the light and meter (no vacuum gauge yet) and found the timing was at around 17 at 1100 rpm. Remember, it was running OK, no pinging even pulling up the hills around Boise on a hot day. I backed it down to 12, reset the idle and never touched the mixture. Started fine, maybe a little surging on idle, not sure yet. On the test drive it ran OK, but maybe did not seem quite as anxious to get up and go.
The other strange thing is that the HVAC system misbehaved when the engine was under load, like it losing the vacuum needed to direct air flow - it moves to the floor vents until the engine load lightens.
So, big question is should I advance the timing back up to the 17 range since it was not pinging before? Little question is does the HVAC behavior indicate a vacuum leak somewhere?
Sorry for the longer post, but the anxiety before the big trip is getting to me. I want to make this as worry free for my wife as possible, as this experience will color everything that comes after.
Thanks,
Jeff
1974/94 GMCII by Explorer
Manny 6.5 TD Al radiator
1 ton front 4 bags back
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| Re: Tune and timing B4 the Big Trip [message #214433 is a reply to message #214424] |
Mon, 15 July 2013 09:42  |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
Karma: 5
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Senior Member |
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Can't help you with the tuning, but I will watch this post to see what they come up with.
but if you are needing an overnight or couple night place to stay, in Central Minnesota. let me know.
St. Cloud, is right on I-94. and I am probably 3 minutes off the interstate.
Jon
Wishing I had time and money to go cross country.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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| Re: Tune and timing B4 the Big Trip [message #214435 is a reply to message #214433] |
Mon, 15 July 2013 09:53 |
xplorid
Messages: 213
Registered: February 2012
Location: Boise
Karma: 0
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Senior Member |
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Thx Jon - I suspect this post might help quite a few newbies. Thx for the overnight offer, but our plan takes us down 84 to 80 at SLC and east from there to Ohio and western NY.
Jeff
1974/94 GMCII by Explorer
Manny 6.5 TD Al radiator
1 ton front 4 bags back
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| Re: [GMCnet] Tune and timing B4 the Big Trip [message #214437 is a reply to message #214424] |
Mon, 15 July 2013 09:58 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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If I were you I'd call Dick Paterson!
Regards,
Rob M.
-----Original Message-----
From: jeff sugheir
About set to leave on our 1st RV trip ID-NY and back, I want to tune the 455. I have a timing light, tach meter, a new vacuum
gauge, and very little experience on this vehicle. I have read all the past posts I could. They seem to say (with a Patterson
distributor on a '76 engine) -
plug the vacuum line to the distributor
set idle at 1100 or set idle at 550-600 (different posts)
aim for 12 deg initial timing with this distributor
reconnect vacuum, start engine, and set idle
adjust the 2 mixture screws on the distributor 1 at a time to max vacuum
reset idle if necessary
drive it and adjust from there, with pinging under load as the guideline for further timing adjustments.
Something like that. So here's my thing: I drove from Florida to here last year after purchase, and other than some vapor lock it
ran well enough, 9+mpg, and about a quart of oil every 800 miles.
Last fall the distributor failed because of an improperly mounted cap and rotor so I bought the Springfield Ignition thru Applied.
A GMC buddy here (another Jim) plopped the new distributor in and dialed it quickly saying "that sounds about right". Ran great and
I did not think about again until this weekend, prepping for the big trip.
So, I hooked up the light and meter (no vacuum gauge yet) and found the timing was at around 17 at 1100 rpm. Remember, it was
running OK, no pinging even pulling up the hills around Boise on a hot day. I backed it down to 12, reset the idle and never
touched the mixture. Started fine, maybe a little surging on idle, not sure yet. On the test drive it ran OK, but maybe did not
seem quite as anxious to get up and go.
The other strange thing is that the HVAC system misbehaved when the engine was under load, like it losing the vacuum needed to
direct air flow - it moves to the floor vents until the engine load lightens.
So, big question is should I advance the timing back up to the 17 range since it was not pinging before? Little question is does
the HVAC behavior indicate a vacuum leak somewhere?
Sorry for the longer post, but the anxiety before the big trip is getting to me. I want to make this as worry free for my wife as
possible, as this experience will color everything that comes after.
Thanks,
Jeff
--
1973/94 GMCII in Boise 76 455 with headers & Patterson distributor,1 ton front, 4 bags back, Precision Steering Gearbox
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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] Tune and timing B4 the Big Trip [message #214439 is a reply to message #214437] |
Mon, 15 July 2013 10:08 |
sgltrac
Messages: 2797
Registered: April 2011
Karma: 1
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Senior Member |
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I second Robs suggestion.
Todd Sullivan
Sully
77 royale
Seattle
On Jul 15, 2013, at 7:58 AM, "Rob Mueller" <robmueller@iinet.net.au> wrote:
> If I were you I'd call Dick Paterson!
>
> Regards,
> Rob M.
>
> -----Original Message-----
> From: jeff sugheir
>
> About set to leave on our 1st RV trip ID-NY and back, I want to tune the 455. I have a timing light, tach meter, a new vacuum
> gauge, and very little experience on this vehicle. I have read all the past posts I could. They seem to say (with a Patterson
> distributor on a '76 engine) -
>
> plug the vacuum line to the distributor
> set idle at 1100 or set idle at 550-600 (different posts)
> aim for 12 deg initial timing with this distributor
> reconnect vacuum, start engine, and set idle
> adjust the 2 mixture screws on the distributor 1 at a time to max vacuum
> reset idle if necessary
> drive it and adjust from there, with pinging under load as the guideline for further timing adjustments.
>
> Something like that. So here's my thing: I drove from Florida to here last year after purchase, and other than some vapor lock it
> ran well enough, 9+mpg, and about a quart of oil every 800 miles.
>
> Last fall the distributor failed because of an improperly mounted cap and rotor so I bought the Springfield Ignition thru Applied.
> A GMC buddy here (another Jim) plopped the new distributor in and dialed it quickly saying "that sounds about right". Ran great and
> I did not think about again until this weekend, prepping for the big trip.
>
> So, I hooked up the light and meter (no vacuum gauge yet) and found the timing was at around 17 at 1100 rpm. Remember, it was
> running OK, no pinging even pulling up the hills around Boise on a hot day. I backed it down to 12, reset the idle and never
> touched the mixture. Started fine, maybe a little surging on idle, not sure yet. On the test drive it ran OK, but maybe did not
> seem quite as anxious to get up and go.
>
> The other strange thing is that the HVAC system misbehaved when the engine was under load, like it losing the vacuum needed to
> direct air flow - it moves to the floor vents until the engine load lightens.
>
> So, big question is should I advance the timing back up to the 17 range since it was not pinging before? Little question is does
> the HVAC behavior indicate a vacuum leak somewhere?
>
> Sorry for the longer post, but the anxiety before the big trip is getting to me. I want to make this as worry free for my wife as
> possible, as this experience will color everything that comes after.
>
> Thanks,
> Jeff
> --
> 1973/94 GMCII in Boise 76 455 with headers & Patterson distributor,1 ton front, 4 bags back, Precision Steering Gearbox
>
>
> _______________________________________________
> GMCnet mailing list
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> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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Sully
77 Royale basket case.
Future motorhome land speed record holder(bucket list)
Seattle, Wa.
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| Re: [GMCnet] Tune and timing B4 the Big Trip [message #214444 is a reply to message #214439] |
Mon, 15 July 2013 10:57 |
Emery Stora
Messages: 959
Registered: January 2011
Karma: 4
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Senior Member |
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Jeff
You will find that it will be more peppy at higher advance but it is very important that it not ping. If you are not sure or if your hearing in a little impaired have someone else listen.
You will find that at higher elevations it will accept more advance without pinging. When I lived in Santa Fe at. 7300 feet I could advance it to 30 degrees with no pinging.
Boise, at 2700 feet, can tolerate more than 12 degrees base setting. If you are sure it doesn't ping go ahead with the 17 degrees.
Jim Kanomata at Applied GMC sells a MSD system which allows you to dial in the advance. It works well.
Emery Stora
77 Kingsley
Frederick, CO
On Jul 15, 2013, at 7:08 AM, Todd Sullivan <sgltrac@gmail.com> wrote:
> I second Robs suggestion.
>
> Todd Sullivan
>
> Sully
> 77 royale
> Seattle
> On Jul 15, 2013, at 7:58 AM, "Rob Mueller" <robmueller@iinet.net.au> wrote:
>
>> If I were you I'd call Dick Paterson!
>>
>> Regards,
>> Rob M.
>>
>> -----Original Message-----
>> From: jeff sugheir
>>
>> About set to leave on our 1st RV trip ID-NY and back, I want to tune the 455. I have a timing light, tach meter, a new vacuum
>> gauge, and very little experience on this vehicle. I have read all the past posts I could. They seem to say (with a Patterson
>> distributor on a '76 engine) -
>>
>> plug the vacuum line to the distributor
>> set idle at 1100 or set idle at 550-600 (different posts)
>> aim for 12 deg initial timing with this distributor
>> reconnect vacuum, start engine, and set idle
>> adjust the 2 mixture screws on the distributor 1 at a time to max vacuum
>> reset idle if necessary
>> drive it and adjust from there, with pinging under load as the guideline for further timing adjustments.
>>
>> Something like that. So here's my thing: I drove from Florida to here last year after purchase, and other than some vapor lock it
>> ran well enough, 9+mpg, and about a quart of oil every 800 miles.
>>
>> Last fall the distributor failed because of an improperly mounted cap and rotor so I bought the Springfield Ignition thru Applied.
>> A GMC buddy here (another Jim) plopped the new distributor in and dialed it quickly saying "that sounds about right". Ran great and
>> I did not think about again until this weekend, prepping for the big trip.
>>
>> So, I hooked up the light and meter (no vacuum gauge yet) and found the timing was at around 17 at 1100 rpm. Remember, it was
>> running OK, no pinging even pulling up the hills around Boise on a hot day. I backed it down to 12, reset the idle and never
>> touched the mixture. Started fine, maybe a little surging on idle, not sure yet. On the test drive it ran OK, but maybe did not
>> seem quite as anxious to get up and go.
>>
>> The other strange thing is that the HVAC system misbehaved when the engine was under load, like it losing the vacuum needed to
>> direct air flow - it moves to the floor vents until the engine load lightens.
>>
>> So, big question is should I advance the timing back up to the 17 range since it was not pinging before? Little question is does
>> the HVAC behavior indicate a vacuum leak somewhere?
>>
>> Sorry for the longer post, but the anxiety before the big trip is getting to me. I want to make this as worry free for my wife as
>> possible, as this experience will color everything that comes after.
>>
>> Thanks,
>> Jeff
>> --
>> 1973/94 GMCII in Boise 76 455 with headers & Patterson distributor,1 ton front, 4 bags back, Precision Steering Gearbox
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: Tune and timing B4 the Big Trip [message #214446 is a reply to message #214424] |
Mon, 15 July 2013 11:13 |
xplorid
Messages: 213
Registered: February 2012
Location: Boise
Karma: 0
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Senior Member |
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Thx all - I just dialed this in "by ear" (not hearing impaired - yet), checked timing and it is a bit beyond the toothed indicator. About to go test it on the freeway going uphill for ping. Dr. Hubler says forget about the timing light, push the advance until it pings then back off ever so slightly. Call in to Dick Paterson. I'll check back in a bit for those of you watching.
Jeff
1974/94 GMCII by Explorer
Manny 6.5 TD Al radiator
1 ton front 4 bags back
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| Re: Tune and timing B4 the Big Trip [message #214447 is a reply to message #214424] |
Mon, 15 July 2013 11:27 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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Senior Member |
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Sir: The way I do mine: Idle needs to be about 700 or less. I would think that 1100 rpm would be allowing the mechanical advance to start moving which would give you a false initial setting. With the rpm at 700 set timing at 14* ( I do run hi-test). If you run the cheep stuff, 8-10* or as much as you can without spark knock under load. If you hi-rpm stall the tranny to check for spark knock do only for a couple of seconds as it heats the tranny fast. With the vacuum gauge set idle at 650-700 rpm and adjust the idle mixtures till they sound the same and run the smoothest at max vacuum. Do it slow as the engine needs a few seconds between adjustments to level out. Run your hands along the plug wires while running, if you get shocked, replace them. A new air filter & fuel filter does help.
| xplorid wrote on Mon, 15 July 2013 09:55 |
About set to leave on our 1st RV trip ID-NY and back, I want to tune the 455. I have a timing light, tach meter, a new vacuum gauge, and very little experience on this vehicle. I have read all the past posts I could. They seem to say (with a Patterson distributor on a '76 engine) -
plug the vacuum line to the distributor
set idle at 1100 or set idle at 550-600 (different posts)
aim for 12 deg initial timing with this distributor
reconnect vacuum, start engine, and set idle
adjust the 2 mixture screws on the distributor 1 at a time to max vacuum
reset idle if necessary
drive it and adjust from there, with pinging under load as the guideline for further timing adjustments.
Something like that. So here's my thing: I drove from Florida to here last year after purchase, and other than some vapor lock it ran well enough, 9+mpg, and about a quart of oil every 800 miles.
Last fall the distributor failed because of an improperly mounted cap and rotor so I bought the Springfield Ignition thru Applied. A GMC buddy here (another Jim) plopped the new distributor in and dialed it quickly saying "that sounds about right". Ran great and I did not think about again until this weekend, prepping for the big trip.
So, I hooked up the light and meter (no vacuum gauge yet) and found the timing was at around 17 at 1100 rpm. Remember, it was running OK, no pinging even pulling up the hills around Boise on a hot day. I backed it down to 12, reset the idle and never touched the mixture. Started fine, maybe a little surging on idle, not sure yet. On the test drive it ran OK, but maybe did not seem quite as anxious to get up and go.
The other strange thing is that the HVAC system misbehaved when the engine was under load, like it losing the vacuum needed to direct air flow - it moves to the floor vents until the engine load lightens.
So, big question is should I advance the timing back up to the 17 range since it was not pinging before? Little question is does the HVAC behavior indicate a vacuum leak somewhere?
Sorry for the longer post, but the anxiety before the big trip is getting to me. I want to make this as worry free for my wife as possible, as this experience will color everything that comes after.
Thanks,
Jeff
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C. Boyd
76 Crestmont
East Tennessee
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| Re: Tune and timing B4 the Big Trip [message #214455 is a reply to message #214424] |
Mon, 15 July 2013 12:42 |
xplorid
Messages: 213
Registered: February 2012
Location: Boise
Karma: 0
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Senior Member |
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Thx again for the support.
On my test run engine ran better than ever, but just started to ping under full load, pedal to the floor, long mild uphill climb. Pulled over and retarded the timing just a bit. Re-ran the hill and no ping, ran great, actually accelerated from 65 to 75 by the end of the grade.
Stop and go performance is not quite right, a little stumble/surge behavior (just a little) but at least I have some confidence that we can adjust as needed, as we go from 2500 elevation to 250 in Western NY.
On the HVAC issue, that seems to be exactly the behavior - under full load the diverter does not have enough vacuum and switches from dash to floor until I let up on the gas. Not a big deal, it's all downhill from here to Ohio, right?
Jeff
1974/94 GMCII by Explorer
Manny 6.5 TD Al radiator
1 ton front 4 bags back
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| Re: Tune and timing B4 the Big Trip [message #214471 is a reply to message #214424] |
Mon, 15 July 2013 15:03 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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There are three components to the ignition timing on your engine. Base, vacuum, and centrifugal. A combination of all three of these set the ignition timing for the engine at various engine speeds and loads.
The centrifugal and vacuum advances are dynamic and change continuously as you are driving down the road.
That leaves the base timing which you are trying to read and set. On Dick Paterson's supplied distributors there is an instruction sheet and piece of paper with the advance curve he set the distributor to for your particular vehicle. On it should be the base timing number that he wants you to set the distributor for on installation.
Mine is 12 degrees BTDC using regular 87 gasoline.
To be able to read that with a timing light you need to cripple the vacuum advance (unplug the vacuum hose and plug it). You also need to make sure that the centrifugal advance is not activating.
The easiest way to prevent the centrifugal advance from operating is to run the engine as slow as practical. So in order to set or check the base timing you need the engine as idle or slower which is usually around 500 to 600 rpm.
At the 1100 RPM that you used the centrifugal advance was already starting to activate and what you saw was a combination of base plus some centrifugal advance.
So slow the engine down and set/read your basic timing again. On mine I found it would ping at 14 and not ping at 12 BTDC.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Tune and timing B4 the Big Trip [message #214475 is a reply to message #214424] |
Mon, 15 July 2013 15:17 |
xplorid
Messages: 213
Registered: February 2012
Location: Boise
Karma: 0
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Senior Member |
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Dick P is going to call me back here in a few minutes, but to follow up on the last 2 posts - my reset described above was at under 600 rpm - again, the sweet spot is well beyond the end of the sawtooth scale. It was set with the dist vacuum disconnected and plugged, and the manifold vacuum disconnected and plugged.
This is a JimB rebuilt carb from just a year ago, and it does not appear to be GMCMH or maybe even Olds compared to the diagram above. The distributor advance is connected to a port in the front of the carb, the manifold connection is off the back of the carb. No T, no TVS, just straight connections to either dist or manifold.
Hmmm.
1974/94 GMCII by Explorer
Manny 6.5 TD Al radiator
1 ton front 4 bags back
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| Re: Tune and timing B4 the Big Trip [message #214500 is a reply to message #214424] |
Mon, 15 July 2013 17:11 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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IF your vac and cent are really working, those initial numbers seem high. I would think knock at heavy part throttle would be happening. Test---Hold it at like 2500 RPM and connect/ disconnect vac advance and watch the timing marks to see if it is working. More retarding means more degrees of throttle needed for same output and therefore less vacuum. You probably have a slight vac leak in the HVAC making it more sensitve to vac drop. Check for cracks and pinches in the hoses. I prefer the ported (stock) port on the Qjet left
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Tune and timing B4 the Big Trip [message #214550 is a reply to message #214539] |
Mon, 15 July 2013 21:30 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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I gave up on the 1100 timing a couple of years back as it was just too hard to hit and impossible to check. So, I too went to the 5~600 and no vacuum set. I played with it a little, but I think I settled on 10° with 87 fuel. That was because it would have to be knocking with a big hammer before I could hear it.
Matt [/quote]
You need to borrow my ignition detonation detector. She sits on the front seat and listens for pinging that I can not hear.
She works cheap.
Yes, I know what a knock sensor is.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Tune and timing B4 the Big Trip [message #214574 is a reply to message #214433] |
Tue, 16 July 2013 07:34 |
Steven Ferguson
Messages: 3447
Registered: May 2006
Karma: 0
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Senior Member |
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NON-GMC Jon, my Alma Mater. I remember getting knothole tickets to watch
the St. Cloud Rocks (MN Millers farm team)for 5 cents. Doc Hollenbeck
spanked me into this world. He has a wing of the University named after
him.
Steve F.
On Mon, Jul 15, 2013 at 7:42 AM, Jon Roche <lqqkatjon@gmail.com> wrote:
>
>
> Can't help you with the tuning, but I will watch this post to see what
> they come up with.
>
> but if you are needing an overnight or couple night place to stay, in
> Central Minnesota. let me know.
>
> St. Cloud, is right on I-94. and I am probably 3 minutes off the
> interstate.
>
> Jon
> Wishing I had time and money to go cross country.
> --
> 75 palm beach
> St. Cloud, MN
> http://lqqkatjon.blogspot.com/
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Take care,
Steve
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