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Date: Thu, 24 Apr 2008 10:31:59 -0400
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From: "Dan & Kari Olsen" <olsen25@comcast.net>
Subject: Hard to start 320 - impulse coupling problem?
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LML Gang,

Would love some troubleshooting help on this one...

Engine: Lycoming IO-320-D1B (stock), 330 SNEW, Slick mags (4373 on left,
4370 on right)

Situation: Hard to start.  Starter cranks just fine, engine coughs and
sputters once in a while but doesn't want to start.  Sounds very similar to
being flooded.  I thought this was a new phenomenon but now that I think
about it I was in Phoenix recently and it did a similar thing but I chalked
that up to starting technique since field elevation there is 1,500' and I
live in Colorado at 5,000'.

Diagnostics Performed:
*	Checked timing on mags.  Both are dead on at 25deg BTDC
*	Checked impulse coupling.  I did this by pulling all plugs out of
the cylinders and then connecting the 4 that are driven by the left mag.
Slowly turned the prop and saw each of the 4 plugs fire off with the "snap"
of the impulse coupling.
*	Checked plugs for fuel wetness and fouling.  All plugs were dry and
very clean.
*	Replaced all plugs and tried to start again.  After much cranking
and sputtering it finally caught and ran.  Once running everything is
perfectly normal.  No abnormal behavior and normal leaning behavior, mag
drops, fuel pressure, etc.
*	Performed several shut downs and restarts.  Very difficult to start
after much cranking every time.  Never just fired up like it used to.

Thoughts So Far:
*	I am suspicious of the impulse coupling.  Even though it appears to
be working I wonder if it is fading or shutting off when the starter spins
the prop but the regular ignition mode of the mags does not yet have enough
energy for a solid spark.  I just don't know enough about these Slick mags
to understand the failure modes.
*	First suspected fuel delivery but not any more since the engine ran
just fine once it started.  Also, when cranking the VM1000 shows a fuel flow
of approx 3-6gph, depending on throttle and mixture setting.  The VM1000
actually measures flow through the line, not just pressure as a proxy.

So, does anyone out there have experience with the Slick mags and impulse
coupling failure modes or know how to better test/isolate?  Any other ideas?


Thanks!

Dan Olsen
LNC2 - N320DK
Fort Collins, CO

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