| [GMCnet] Timing question [message #184478] |
Fri, 14 September 2012 16:13  |
glwgmc
Messages: 1014
Registered: June 2004
Karma: 10
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Senior Member |
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I have a new Dick Patterson HEI distributor on my 455. My carb is a Rochester Quadrajet off of something other than a GMC motorhome. It was installed by Mark McNeal at the DynoShop in Santee, CA, when he rebuilt this motor for the previous owner. It has been really strong for over 60,000 miles and still runs like a champ. My timing issue is that the timed vac port on this carb (drivers side front just above the throttle plate) shows 12 to13" of vac at idle instead of the zero that I thought all QJs read on this port. I no longer have the temp controlled valve that switches between timed vac port at low water temps and manifold vac at high water temps. Manifold vac at idle is 16 to 17" and goes well over 20 on downgrades. Cruise is normally 14" to 16" at 60mph flat and level. The engine uses/leaks a quart of oil about every 2000 miles and is very strong.
I can't reach Dick for his suggestion, so will ask the collective wisdom here. He has this distributor set for 10 degrees initial, 20 degrees at 3000 rpm centrifical, zero degrees vac adv at 6" of vac, going up to 10 degrees at 12" for a total of 40 degrees. He said to time it by unplugging and blocking the vac line, reduce idle speed to 400-500 rpm, set initial at 10 degrees BTDC, reconnect the vac line and resetting idle speed to 700 to 800 rpm. I don't know if he was thinking the timed vac port would read zero at idle or not, hence my question.
Since I get 10 degrees of advance at idle just on the timed vac port alone, where should I set the initial when the vac line is disconnected and blocked? If I set initial to 10 degrees then with vac at idle the engine will be seeing 20 degrees of advance and up to 40 degrees at cruise. Under load (low vac) the engine will see 30 degrees at 3000 rpm (the initial 10 plus the 20 centrifical). What is the correct way to time this engine?
Jerry
Jerry Work
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR
glwork@mac.com
http://jerrywork.com
541-592-5360
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Jerry & Sharon Work
78 Royale
Kerby, OR
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| Re: [GMCnet] Timing question [message #184482 is a reply to message #184478] |
Fri, 14 September 2012 16:33  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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Jerry, yes I am stateside and presently at Judy's in San Rafael. We are
cleaning out her house and preparing it for lease. To answer your timing
question, block the vacuum hose to the distributor. On a warmed up engine,
set idle speed to 550 rpm. Set static timing to 10 degrees advance. This
should be very close with the paterson distributor. If you experience
pinging with this much advance, retard timing 2 degrees at a time until it
no longer pings. When you open the throttle, you have less advance, so take
a mity vac pump and verify that your vacuum advance canister still holds
vacuum. They are known to fail. I agree with Dick on his settings. When
you are all done, hot idle should be 500-650 rpm. If it diesels when you
shut down, slow it down a little.
Jim Hupy
Salem or
78GMC Royale 403
On Sep 14, 2012 2:13 PM, "Work Jerry" <glwork@mac.com> wrote:
> I have a new Dick Patterson HEI distributor on my 455. My carb is a
> Rochester Quadrajet off of something other than a GMC motorhome. It was
> installed by Mark McNeal at the DynoShop in Santee, CA, when he rebuilt
> this motor for the previous owner. It has been really strong for over
> 60,000 miles and still runs like a champ. My timing issue is that the
> timed vac port on this carb (drivers side front just above the throttle
> plate) shows 12 to13" of vac at idle instead of the zero that I thought all
> QJs read on this port. I no longer have the temp controlled valve that
> switches between timed vac port at low water temps and manifold vac at high
> water temps. Manifold vac at idle is 16 to 17" and goes well over 20 on
> downgrades. Cruise is normally 14" to 16" at 60mph flat and level. The
> engine uses/leaks a quart of oil about every 2000 miles and is very strong.
>
> I can't reach Dick for his suggestion, so will ask the collective wisdom
> here. He has this distributor set for 10 degrees initial, 20 degrees at
> 3000 rpm centrifical, zero degrees vac adv at 6" of vac, going up to 10
> degrees at 12" for a total of 40 degrees. He said to time it by unplugging
> and blocking the vac line, reduce idle speed to 400-500 rpm, set initial at
> 10 degrees BTDC, reconnect the vac line and resetting idle speed to 700 to
> 800 rpm. I don't know if he was thinking the timed vac port would read
> zero at idle or not, hence my question.
>
> Since I get 10 degrees of advance at idle just on the timed vac port
> alone, where should I set the initial when the vac line is disconnected and
> blocked? If I set initial to 10 degrees then with vac at idle the engine
> will be seeing 20 degrees of advance and up to 40 degrees at cruise. Under
> load (low vac) the engine will see 30 degrees at 3000 rpm (the initial 10
> plus the 20 centrifical). What is the correct way to time this engine?
>
> Jerry
> Jerry Work
> Fine furniture designed and hand crafted in the 1907 former Masonic Temple
> building in historic Kerby, OR
> glwork@mac.com
> http://jerrywork.com
> 541-592-5360
>
>
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] Timing question [message #184490 is a reply to message #184478] |
Fri, 14 September 2012 17:56 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Time it just the same as Dick told you to do. Yes at idle your timing is too far advanced but that will not hurt anything. All it will do is raise your idle speed which you can adjust back down with the idle screw. The ported vacuum port is suppose to present near near 0" of vacuum at idle but the minute you step on the gas that port would give you exactly what you are now seeing so you are just fine.
Dick sets up his distributors to be a total possible 39 to 40 degrees at your cruise RPM which is normally 60 to 65 mph. That is why he asks if you have an other than stock final drive. The 40 degrees is a total of the base + vacuum + mechanical advance. I have my Paterson distributor base set for 12 degrees BTDC rather than 10. I determined that by running on 87 octane fuel and trying various settings until it pinged under heavy acceleration. At 14 it pinged under heavy acceleration and at 12 it doesn't. So 12 it is. At 10 you should not ever have a pinging problem. Just listen for pinging. If you never hear it then you are safe. Advancing it farther might marginally improve some performance and mpg but you are so close now that it probably is not worth the bother.
HTH
Ken B.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
[Updated on: Fri, 14 September 2012 17:59] Report message to a moderator |
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| Re: [GMCnet] Timing question [message #184491 is a reply to message #184478] |
Fri, 14 September 2012 18:16 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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Question I have is why you are leaking vac to the ported port at idle???? Is the base idle setup using that much throttle rotation to be uncovering the port with the blades? Are the throttle plates installed correctly on the shaft? Also remember the real GMC Qjet used a unique triple primary rod but that's another thing. Are you coming to Amana? I'll bring your kit but need help with allignment due to recent hospital stay. I'd love to look at that throttle plate to see wHY?
John Lebetski
Woodstock, IL
77 Eleganza II
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