Thread: Sooty Plugs
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Old 08-14-2019, 02:19 PM
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Warning, long post but there’s a lot to cover

I hooked up with Joe yesterday to take a look at his A4 setup...

Without giving away too much personal info on Joe;
he’s a great young guy who is in active duty serving our country
(his screen name gives you a hint)
with a clean 27’ Newport with pretty decent engine access.

First thing we did was open up the distro cap and check the springs/weights.
They were pristine and nicely lubed.
The cap is brand new and looked fine. (See pic)
The plug wires are in the correct order and in good condition.
Checked the choke and it is opening and closing fine.
Flame Arrestor is good but for initial testing we left it off. (Later, tested with it on)

So we fired her up and she ran really well. Started right up within 2-3 seconds.
Did a couple of throttle revs and she did well. Slight hesitation but good.

There is a small but definite exhaust leak at the flange/manifold joint.
Water flow was very good at the exhaust.

Shut it down and pulled the plugs. They’re definitely sooty. (See pics)
Not wet, just carbon burned. (More on this later)
We gaped them to .040 and re-installed them.

The Idle Mixture screw was indeed at 2.5+ turns out.
Re-set it to 1.5 for a baseline while checking the timing.
Fired her back up...
We didn’t have a timing light, so we ran her up to speed (under load) and did a “power time” rotating the dizzy.
We moved counter-clock (advanced) to err on the lean side.
While still running, we tried turning the idle mixture IN and she got rough.
Turned it OUT and she immediately ran noticeably smoother.
Ended up about 2 ¼ turns OUT.
Finally we adjusted the idle screw to a really smooth idle at around 700-800 RPM.
(Tach isn’t accurate so RPM is “by ear”)

So, after the fine tuning, she definitely sounded and ran a bit smoother.
Did some more throttle revs and she did real well. No hesitation or stumble.
NOTE here...
Smoother - meaning running really well.
Many on this site would wish for their engine running this well.

A few questions I have...
Would that Exhaust Leak be causing the sooty plugs?
Could that loose belt cause the ALT to put out low voltage resulting in rich running? Sooty plugs?

(I didn’t think to check voltage at the coil. My bad)
I also forgot to check if Joe is using the CORRECT spark plugs.
They were Champion and the pics show a 2C, so I think they’re right. (RJ-12C)

Joe is happy with the smooth running engine and is committed to the value of his A4 (vs using an OB)
He has an excellent grasp of the A4 and it’s various systems and functions.
He is very capable and willing to do the servicing tasks as required going forward.

He is just concerned, as anyone should be...
Why does the idle mixture want to be set so LEAN?
Why the sooty plugs?


Summary:
• New Sierra 10m Filter/Separator
• New Polish Filter
• Rebuilt Mechanical Fuel Pump
• Carb was rebuilt recently and “looks” clean
• New MMI 4Ω Coil
• New Distributor Cap
• Small exhaust leak at the manifold/flange (Good water batching tho)
• Very loose Alternator Belt (1.5 - 2” deflection)
• ALL plugs are dry, black sooty after approximately 15+ hours
• Idle Mixture setting wants to be on the Lean side. 2 ¼ turns out
• Engine starts right up and runs smooth

So, I have reached the limits to my “mechanical” knowledge here.
It’s time for the smarter guys to step up.
Thoughts?
Attached Images
    
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-Jerry

'Lone Ranger'

1978 RANGER 30
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