Ignition question
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 6,807
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From: Hoosier
Cruise-In III Veteran
Ignition question
I'm using an MSD 6A box, Blaster 2 coil, MSD 8.5 wires, and a Pertronix Igniter.
Friday night I changed the plug gap from 040 to 045. Saturday I see that the air/fuel gauge is showing mostly real lean at cruise, whereas before at the same cruise speeds it was showing stoich/lean. It runs great and no hint of detonation.
Have you guys seen any relationships between plug gaps and timing and/or carb fuel metering?
Friday night I changed the plug gap from 040 to 045. Saturday I see that the air/fuel gauge is showing mostly real lean at cruise, whereas before at the same cruise speeds it was showing stoich/lean. It runs great and no hint of detonation.
Have you guys seen any relationships between plug gaps and timing and/or carb fuel metering?
Safety Car
Joined: Jun 2001
Posts: 4,004
Likes: 2
From: Severna Park Md
Re: Ignition question (AlwaysWave)
You might be getting better combustion now with the larger gap. Less unburnt fuel will result in a leaner reading wouldnt it? Temperature drops will lean things out a bit too. Cooler denser air in the mixture. Changing the plug gap should not have an effect on the ignition timing.
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 6,807
Likes: 0
From: Hoosier
Cruise-In III Veteran
Re: Ignition question (Jvette73)
You might be getting better combustion now with the larger gap. Less unburnt fuel will result in a leaner reading wouldnt it? Temperature drops will lean things out a bit too. Cooler denser air in the mixture. Changing the plug gap should not have an effect on the ignition timing.
Melting Slicks
Joined: Jun 2001
Posts: 2,340
Likes: 2
From: Moro IL
Re: Ignition question (AlwaysWave)
Air fuel gauges, simply read oxygen in the exhaust nothing else. Therefore it doesn't really know the A/F ratio but gives an indication of it from the amount of oxygen in the exhaust. Now if by increasing the gap you may have caused some partial misfires and the Oxygen sensor will pick this up as a lean or leaner reading since a partial miss will leave left over oxygen in the exhaust system for the A/F sensor to pick up. This is one possibilty, easy enought to tell by gapping the plugs back to 40
:cheers:
Pat Kunz
:cheers:
Pat Kunz
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 6,807
Likes: 0
From: Hoosier
Cruise-In III Veteran
Re: Ignition question (73 LS-4)
It doesn't run like there's any misfires. Today I went a bit richer on the primary jetting. It runs even stronger and the gauge is much more into the stoich range. I'm intrigued by this.
