Home » Public Forums » GMCnet » Quadrajet? question (Uneven idle)
| Quadrajet? question [message #363979] |
Thu, 13 May 2021 22:28  |
dsmithy
Messages: 210
Registered: July 2012
Location: Lincoln Nebraska
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Dear people smarter than I,
I'm asking what I hope is a simple question.
I have a five year old or so Quadrajet from Dick Paterson which I trust completely.
After running for quite a while with what I thought might be somewhat retarded timing, I advanced it about 10 degrees. Coach runs better and seems much happier, no pre-ignition, no problems at speed. I suspect my mileage will improve with the lower throttle settings to maintain speed.
BUT...
At idle, it surges slightly, enough to wake the tranny intermittently. Not a big problem, but my previous idle was rock solid.
Do I dare touch the idle, the idle mixture, or am I party to some other issue beyond my (limited) knowledge?
There seems to be many potholes in the road to perfection. Can you help?
Doug
Douglas & Virginia Smith,
dsmithy18 at gmail,
Lincoln Nebraska,
’73 “Sequoia” since ‘95: "Wanabizo";
Quadrabag/6 wheel disks/3:70 final/Paterson QuadraJet/Thorley’s/Alloy wheels/Sundry other
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| [GMCnet] Re: Quadrajet? question [message #363981 is a reply to message #363979] |
Thu, 13 May 2021 22:50  |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Since you advanced the timing, your idel speed went up and you need to slow
it down and slowly work on the idle jets.
On Thu, May 13, 2021 at 8:28 PM Douglas Smith wrote:
> Dear people smarter than I,
> I'm asking what I hope is a simple question.
> I have a five year old or so Quadrajet from Dick Paterson which I trust
> completely.
> After running for quite a while with what I thought might be somewhat
> retarded timing, I advanced it about 10 degrees. Coach runs better and seems
> much happier, no pre-ignition, no problems at speed. I suspect my mileage
> will improve with the lower throttle settings to maintain speed.
>
> BUT...
> At idle, it surges slightly, enough to wake the tranny intermittently. Not
> a big problem, but my previous idle was rock solid.
> Do I dare touch the idle, the idle mixture, or am I party to some other
> issue beyond my (limited) knowledge?
> There seems to be many potholes in the road to perfection. Can you help?
> Doug
>
> --
> Douglas & Virginia Smith,
> dsmithy18 at gmail,
> Lincoln Nebraska,
> ’73 “Sequoia” since ‘95: "Wanabizo";
> Quadrabag/6 wheel disks/3:70 final/Paterson QuadraJet/Thorley’s/Alloy
> wheels/Sundry other
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.gmcrvparts.com
1-800-752-7502
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| Re: Quadrajet? question [message #363989 is a reply to message #363979] |
Fri, 14 May 2021 11:20 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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dsmithy wrote on Thu, 13 May 2021 23:28Dear people smarter than I,
I'm asking what I hope is a simple question.
I have a five year old or so Quadrajet from Dick Paterson which I trust completely.
After running for quite a while with what I thought might be somewhat retarded timing, I advanced it about 10 degrees. Coach runs better and seems much happier, no pre-ignition, no problems at speed. I suspect my mileage will improve with the lower throttle settings to maintain speed.
BUT...
At idle, it surges slightly, enough to wake the tranny intermittently. Not a big problem, but my previous idle was rock solid.
Do I dare touch the idle, the idle mixture, or am I party to some other issue beyond my (limited) knowledge?
There seems to be many potholes in the road to perfection. Can you help?
Doug
Doug,
You did not say if the ignition is original. If it has been changed to HEI, there may be other problems.
If it still has points, go get a Pertronix 1181LS and install that set. This won't fix anything immediately, but you will have more stable ignition.
If you are trying to set the timing like Olds says, you have a problem. The spec if 10° @ 1100 is a moving target because that is the beginning of mechanical advance.
If you set 8~10° at a slow idle, that is usually close, but there is still variation between engines.
Now, if that is where you were and you could advance 10° from there, something was wrong. If I did that, the engine would probably blow up. This leads me to wonder if you timing marks are good.
Do you know how to check that? If not, I can walk you through that. Sometimes, the ring on the damper slips, this is easy to check, but you have to take the FEAD drive sheave off the damper to see if it was marked.
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: Quadrajet? question [message #363999 is a reply to message #363989] |
Fri, 14 May 2021 14:07 |
dsmithy
Messages: 210
Registered: July 2012
Location: Lincoln Nebraska
Karma: 0
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Matt,
Thanks for your thoughtful answers.
I do have the Pertronix lobe sensing unit, and with the matching coil. I have a timing light, but have never successfully stood on my head and used it on the timing mark. Since the coach has always started well and run well, I thought I must be close. I just had the feeling that I was using a little more throttle to hold speed than seemed right. Acting on the thread in this forum where someone said to just pay attention to how it runs and advance it till it pings and back it off, I elected to approach that point from the more conservative direction so I just advanced it about 10 degrees by sight and clamped it down. The engine ran a LOT easier, and with less throttle input. Based on that success I advanced it another 5 degrees or so. Still no pre-ignition and it seems to be a happier engine except for the idle surging. The idle does not seem to have increased in rpms. I have found no vacuum leaks either. I am reluctant to adjust anything on Dick Paterson's rebuild of the Quadrajet but suspect that may be next. Thoughts?
Doug
Douglas & Virginia Smith,
dsmithy18 at gmail,
Lincoln Nebraska,
’73 “Sequoia” since ‘95: "Wanabizo";
Quadrabag/6 wheel disks/3:70 final/Paterson QuadraJet/Thorley’s/Alloy wheels/Sundry other
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| Re: Quadrajet? question [message #364007 is a reply to message #363979] |
Fri, 14 May 2021 18:37 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Lots of “ that make no sense” info here. 10 Degrees is a HUGE change in timing where a Couple degrees makes a big difference. Yes your idle would speed up as you advance, up till the point where it gets rough and RPM drops. This COULD be the problem. Since you have not messed with the Qjet (but blamed it!) I will not go into idle mixture adjustment at this point as you have messed with one variable (timing) and this could really complicate things. You need to see what base timing really is and if VACUUM and MECHANICAL advance are both free and working correctly.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Quadrajet? question [message #364009 is a reply to message #363999] |
Fri, 14 May 2021 20:38 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Doug,
John is right that the changes you are making are big, but I think you are looking at the amount you have moved the distributor. Typical timing numbers refer to the crankshaft, those number will be half of what you have moved the distributor.
I will at this time, strongly suggest that you get out your "belly board" that spans the engine hatch and connect your timing light and find out where your timing really is right now. If you get an occasional ping at WOT that can be survived, more than occasional can be very damaging.
Yes, it it a real pain checking the timing on these coaches, but I haven't written up my alternative procedure as yet and you need to do this NOW.
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: Quadrajet? question [message #364013 is a reply to message #364009] |
Fri, 14 May 2021 23:27 |
dsmithy
Messages: 210
Registered: July 2012
Location: Lincoln Nebraska
Karma: 0
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John and Matt,
You probably just saved my bacon. I had no idea that the distributor rotation was double the degrees at the crankshaft. I will immediately retard the last "correction" I did. I will be driving 400 miles tomorrow and could probably have done real damage with the timing where its at. Thanks a thousand times. Since we intend to park the coach at a seasonal spot I will have plenty of time to look at the timing marks and balancer. BTW John, I have checked the weights for freedom of motion and put a vacuum on the distributor to verify the advance is working. I think you both nailed it by saying I've probably just over advanced the timing and haven't verified that at highway speeds and loads.
I know I'm not the first to unwittingly consider a friendly and very old motorhome a coarse and simple beast. I learn daily that there is more subtlety and finesse buried in our old coach than I will likely ever learn. Thanks to both of you for this latest lesson.
Doug
Douglas & Virginia Smith,
dsmithy18 at gmail,
Lincoln Nebraska,
’73 “Sequoia” since ‘95: "Wanabizo";
Quadrabag/6 wheel disks/3:70 final/Paterson QuadraJet/Thorley’s/Alloy wheels/Sundry other
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| Re: Quadrajet? question [message #364016 is a reply to message #363979] |
Sat, 15 May 2021 07:35 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Here is another way “By Ear” if no other way to set rough timing. Engine warm and idling and dist hold down just allowing hand rotation of dist play with setiing finding MAX idle RPM spot in the range. That will be too advanced for real world use. Retard from there until you get about a 50-100 RPM drop. At this point you can start to road test and make fine adjustments to the edge of ping under worst conditions. Snug the hold down! I put down white tape on my aluminum just behind dist and use a straight edge off edge of HEI flat. I have a sea level max and mountains max advance sharpie line marks so when going through elevation changes I can know my range and inbetween when high plains.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Quadrajet? question [message #364017 is a reply to message #364015] |
Sat, 15 May 2021 07:43 |
dsmithy
Messages: 210
Registered: July 2012
Location: Lincoln Nebraska
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Larry,
We'll be over in Park Rapids, MN for most of the summer. We will definitely see you and I intend to be at the fall rally in Chippewa Falls.
Douglas & Virginia Smith,
dsmithy18 at gmail,
Lincoln Nebraska,
’73 “Sequoia” since ‘95: "Wanabizo";
Quadrabag/6 wheel disks/3:70 final/Paterson QuadraJet/Thorley’s/Alloy wheels/Sundry other
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| Re: Quadrajet? question [message #364019 is a reply to message #364017] |
Sat, 15 May 2021 08:10 |
Larry
Messages: 2875
Registered: January 2004
Location: Menomonie, WI
Karma: 10
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dsmithy wrote on Sat, 15 May 2021 07:43Larry,
We'll be over in Park Rapids, MN for most of the summer. We will definitely see you and I intend to be at the fall rally in Chippewa Falls.
Doug,
Well, that is up there in Minnesota near Bemidji. Gods country!!
If it fits in your schedule, the Greater Midwest Classics GMC Motorhome club is having our spring rally in Nelson Wisconsin, June 4, 5, 6 with early arrival on the 3rd. You are welcome to join us.
Have a good summer up there....a great place to be.
Larry 
78 Royale w/500 Caddy
Menomonie, WI.
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| [GMCnet] Re: Quadrajet? question [message #364021 is a reply to message #364019] |
Sat, 15 May 2021 08:55 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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The only reason I don't jump and shout everything someone suggests setting
the ignition timing "by ear" is this: with all the Oldsmobile engines that
I have worked on since about 1959, (and that's a whole bunch of them)
starting with a 303 out of a 1949 Olds Convertible, that I found in a
salvage yard that I rescued to put in my 1938 Olds sedan. That was where I
first learned about hydraulic lifter camshafts not being compatible with
solid lifters and adjustable rocker arms in Olds engines.
Also learned about the inaccuracy of factory timing marks, pointers
stamped from sheet metal and bolted on rather than a permanent part of the
engines.
455's are not any better in that respect. Everything from crankcase
keyways cut in the wrong place, cam sprockets, timing chain teeth, hobbling
holes and pins in the wrong place, aftermarket camshafts with the lobes and
distributor gears in the wrong places, etc., etc.
So my point is this. If the factory builds 300 of these things in an 8
hour shift, how accurate are the factory marks? Truth is, they AIN'T ANY
CLOSER THAN SETTING THE TIMING "BY EAR".
So have at it, odds are the same either way of it being wrong.
Jim Hupy
Salem, Oregon
On Sat, May 15, 2021, 6:10 AM Larry wrote:
> dsmithy wrote on Sat, 15 May 2021 07:43
>> Larry,
>> We'll be over in Park Rapids, MN for most of the summer. We will
> definitely see you and I intend to be at the fall rally in Chippewa Falls.
>
> Doug,
>
> Well, that is up there in Minnesota near Bemidji. Gods country!!
>
> If it fits in your schedule, the Greater Midwest Classics GMC Motorhome
> club is having our spring rally in Nelson Wisconsin, June 4, 5, 6 with early
> arrival on the 3rd. You are welcome to join us.
>
> Have a good summer up there....a great place to be.
> --
> Larry
> 78 Royale w/500 Caddy
> Menomonie, WI.
> _______________________________________________
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| Re: Quadrajet? question [message #364095 is a reply to message #364015] |
Mon, 17 May 2021 21:25 |
dsmithy
Messages: 210
Registered: July 2012
Location: Lincoln Nebraska
Karma: 0
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Update:
I backed off over half of my advance and that cleared up the idle problem. Because it is somewhat advanced from its former position I do notice that the engine runs easier with less throttle input, no discernable ping, and no overheating issues. Win, win, win. I do intend, while I sit here to time it properly.
Matt, we know so many people scattered around MN that the coach won't sit for anything like weeks, much less months, so I don't think varnish will be a problem.
Larry, as it happens Va is directing a play that rehearses in CO that week, so I will be going back to NE that week to put her on an airplane from Omaha, do a weeks worth of projects around the homestead and then scurry us both back to MN and the coach. Sorry to miss your rally.
Jim, I don't disagree at all. Having said that, do you think John's method of finding the fastest idle with a warm engine and backing off 100 or so rpm with timing is a good place to start?
Douglas & Virginia Smith,
dsmithy18 at gmail,
Lincoln Nebraska,
’73 “Sequoia” since ‘95: "Wanabizo";
Quadrabag/6 wheel disks/3:70 final/Paterson QuadraJet/Thorley’s/Alloy wheels/Sundry other
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| [GMCnet] Re: Quadrajet? question [message #364100 is a reply to message #364095] |
Mon, 17 May 2021 23:44 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Geez, I hate to deal with that method by adding my opinion to it.
But, that being said, I have said many things that others did not
agree with.
Without a TDC mark actually verified by precision tools, none of the
various methods have much going for them.
Rule of thumb for me, I guess, would be to listen to the starter when
cranking a warmed up engine. If it cranks like it is having difficulty
turning the engine over, it is very likely that there is too much static
advance.
Conversely, if the engine spins over easily but fails to start right
up, one cause might be that the static timing is too retarded.
I know, I know, there are a whole bunch of variables in those
statements. But, a heavily loaded engine, working hard, will self destruct
very quickly if it has too much retard. If there is too much advance, it
should ping as a warning before that happens.
Those are general statements, I know. You just have to have 40 years
of experience with these critters to know the difference. But exactness in
timing is subjective to about a Jillion variables. Load variations,
altitude, fuel quality, carb and distributor conditions, etc., etc. That's
all I got.
Jim Hupy
Salem, Oregon
On Mon, May 17, 2021, 7:25 PM Douglas Smith wrote:
> Update:
> I backed off over half of my advance and that cleared up the idle problem.
> Because it is somewhat advanced from its former position I do notice that
> the engine runs easier with less throttle input, no discernable ping, and
> no overheating issues. Win, win, win. I do intend, while I sit here to time
> it properly.
>
> Matt, we know so many people scattered around MN that the coach won't sit
> for anything like weeks, much less months, so I don't think varnish will be
> a problem.
>
> Larry, as it happens Va is directing a play that rehearses in CO that
> week, so I will be going back to NE that week to put her on an airplane from
> Omaha, do a weeks worth of projects around the homestead and then scurry
> us both back to MN and the coach. Sorry to miss your rally.
>
> Jim, I don't disagree at all. Having said that, do you think John's method
> of finding the fastest idle with a warm engine and backing off 100 or so
> rpm with timing is a good place to start?
> --
> Douglas & Virginia Smith,
> dsmithy18 at gmail,
> Lincoln Nebraska,
> ’73 “Sequoia” since ‘95: "Wanabizo";
> Quadrabag/6 wheel disks/3:70 final/Paterson QuadraJet/Thorley’s/Alloy
> wheels/Sundry other
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
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