More ignition help needed! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Dingfodgy · 08-24-2008, 11:17 PM

Yesterday, many of ya'll chimed in and suggested that my GMC wouldn't fire 'cause the dizzy was 180* out.....you were right! Today I went out to set the timing and for the life of me I cant get this persistent backfire shortly off idle to go away. This leads me to a couple questions.
1. Should the vacuum advance be connected or disconnected to set initial timing?
2. My timing tab has no numbers on it....anybody have an idea what the graduations might be? I guessed that the lines went in 2* intervals, but maybe they're actually 1*....I dunno. (See Pic). Oh yeah, and why do I have two tabs with different markings...which should I use?
Name: Timing Mark.JPG
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Name: Timing Mark.JPG
Views: 191
Size: 33.0 KB

piecesparts · 08-24-2008, 11:21 PM

Set the timing with the vacuum DISCONNECTED from the dizzy.

Looking at your pictures, I would sumise that the "0" is the TDC of your timing. The "A" simbalizes the adavance direction and I would also surmise that each mark is 2 degrees advance. So for a bottom line, set the timing at the 10 degree mark and work from there.

chipflyer · 08-24-2008, 11:24 PM

Check your plug wire order, good bet you have 2 wires switched.
You should have vacuum unhooked from dizzy and the line plugged.
Make sure you set the idle first, otherwise you could have mechanical advance coming in when trying to set the initial.
Not sure on that tab, I would remove plug #1, find TDC and mark it.

Jeff

sneakysnake · 08-25-2008, 12:39 PM

v-8.. 1-8-4-3-6-5-7-2

i6...1-5-3-6-2-4

68gmsee · 08-25-2008, 02:17 PM

The graduation should be in 2's on your timing tab. Looks like someone added an extra tab. Not sure why, but if they're fairly close, just get with range and then tweak it until you get it running smooth.

Also, when you disconnect the vacuum advance, be sure and plug the hose going to the carb if you're connected to engine vacuum.

I had a miss on my GMC that I fixed by replacing the plugs. They all looked good, but evidently one of them was bad. They have internal parts than can go bad.

Here's an example...

Wrenchbender Ret · 08-25-2008, 04:16 PM

If it was running when you took that photo your timing is too slow. Start out about on the A & tailor it from there.

08-24-2008, 11:21 PM	#2
piecesparts Parts and more parts Join Date: Nov 2003 Location: Lebo, Kansas (middle of nowhere Posts: 6,821	Re: More ignition help needed! Set the timing with the vacuum DISCONNECTED from the dizzy. Looking at your pictures, I would sumise that the "0" is the TDC of your timing. The "A" simbalizes the adavance direction and I would also surmise that each mark is 2 degrees advance. So for a bottom line, set the timing at the 10 degree mark and work from there.

08-24-2008, 11:24 PM	#3
chipflyer Registered User Join Date: May 2004 Location: Topeka, Ks Posts: 2,293	Re: More ignition help needed! Check your plug wire order, good bet you have 2 wires switched. You should have vacuum unhooked from dizzy and the line plugged. Make sure you set the idle first, otherwise you could have mechanical advance coming in when trying to set the initial. Not sure on that tab, I would remove plug #1, find TDC and mark it. Jeff __________________ I'm not a pessimist, I'm just optimistic that bad things are going to happen. 1971 Cheyenne Super K10 - tilt, cruise, air, am/fm, tow hooks, factory buckets! 1986 Jeep J10 pickup, - 5.3L Vortec with 4L60e and NP241.

08-25-2008, 12:39 PM	#4
sneakysnake It's a catastrophic success. Join Date: Jan 2003 Location: Oklahoma Posts: 2,077	Re: More ignition help needed! v-8.. 1-8-4-3-6-5-7-2 i6...1-5-3-6-2-4 Attached Images

08-25-2008, 02:17 PM	#5
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: More ignition help needed! The graduation should be in 2's on your timing tab. Looks like someone added an extra tab. Not sure why, but if they're fairly close, just get with range and then tweak it until you get it running smooth. Also, when you disconnect the vacuum advance, be sure and plug the hose going to the carb if you're connected to engine vacuum. I had a miss on my GMC that I fixed by replacing the plugs. They all looked good, but evidently one of them was bad. They have internal parts than can go bad. Here's an example... Attached Images

08-25-2008, 04:16 PM	#6
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,228	Re: More ignition help needed! If it was running when you took that photo your timing is too slow. Start out about on the A & tailor it from there.

08-24-2008, 11:17 PM	#1
Dingfodgy Lemme show you something!! Join Date: Apr 2007 Location: St.Helens, OR. Posts: 876	More ignition help needed! Yesterday, many of ya'll chimed in and suggested that my GMC wouldn't fire 'cause the dizzy was 180* out.....you were right! Today I went out to set the timing and for the life of me I cant get this persistent backfire shortly off idle to go away. This leads me to a couple questions. 1. Should the vacuum advance be connected or disconnected to set initial timing? 2. My timing tab has no numbers on it....anybody have an idea what the graduations might be? I guessed that the lines went in 2* intervals, but maybe they're actually 1....I dunno. (See Pic). Oh yeah, and why do I have two tabs with different markings...which should I use? __________________ '67 CST-10 LWB ("Crusty") SOLD* '67 GMC SWB ("Murdock") 2000 K1500 Suburban ("Betty") '95 BMW 325i ("Joy")



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