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Ignition Timing with Vortec heads

marada1

Regular Contributor
"Need some help in finding bes

"Need some help in finding best timing setting. My engine is a 1990 4.3. I have added Vortec heads and Edelbrock intake and 4bbl carb. With the new setup there is no manual that tells me where to set the timing. Engine was originally a 2bbl and timing spec was 1dbtdc with 86-88 octane, 6dbtdc with 89 octane. I was running it at 6deg then with reg fuel because thats where it ran the best. With the new setup I have been running it at 8deg. I set it at 8 because thats the spec for the 97-98 model vortecs. I think those engines were fuel injected and it's not really an apples to apples comparison. If I set it at 6deg now with the new setup it simply will not idle. It will idle at 8deg but it's a little rough and dies occasionally. I have adjusted idle mixture until I have nearly worn out the screws. Idle is much smoother at 10 deg and up. I ran it this morning and played with the timing some. Ran it at 10 deg and at 12 deg (a little) and ended up leaving it at 10. I am a little afraid to run it any higher for fear of detonation. I did not hear any pinging in the engine during these runs. Will the spark plugs tell the story if I have detonation before damage is done? Should I be able to hear it?
Thanks"
 
"[b]"Will the spark plugs

""Will the spark plugs tell the story if I have detonation"
"I have adjusted idle mixture until I have nearly worn out the screws."


Ayuh,.....

The Plugs will tell their story,... I'd keep the WOT test runs short though...
And,...
It sounds like you need to sort out the Carb too...
Eldebrock has a Great on-line carb Manual for their Performer series...."
 
"Made a big find today! Bondo,

"Made a big find today! Bondo, you got me think'in with your suggestion on the carb. From day one with this (new) carb the port side mixture screw never really had much effect on the idle. The other screw, however had big effect and I believe it was suppling all the idle fuel. I also have had a surging condition at light throttle. I had removed the carb and disassembled it and checked the idle circuit and found nothing plugged. Anyway, after Bondo's post I decided to pull the carb again. Almost overlooked it again but stuck to the bottom of the port side reservoir for the primary venturi booster I found a blob of what looks like some sort of epoxy material. It's about the size of a pencil eraser and very clear so hard to see. The pick-up tube for the venturi was sitting on top of this "blob" and almost certainly restricting fuel flow.
I have high hopes that this will solve several problems I have been having, poor idle, light throttle surge, and there's a good chance I'll see better WOT performance too. I'll set the timing back to 8 and head to the river in a day or two to check it out. I'll let you guys know how it goes."
 
"WOW! What a difference! Ran

"WOW! What a difference! Ran it on muffs today and now it purrs like a kitten at idle.
happy.gif
"The Blob" definately had the port side idle circuit blocked. Can't wait to get it in the water and see how much it was affecting the primary circuit. It was sort of stumbbling on hole shot before so hopefully that will be better and maybe WOT as well.
Thanks again Bondo! Sometimes it makes all the difference to have someone jump-start our brain!
Think I'll mail "The Blob" to Edelbrock and tell them they owe me a tank of fuel!
lol.gif
"
 
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