Al, and
Don,
I also
observed weak / intermittent spark on one rotor when I was working on my
hard-to-start issue. I later found
that on one of my plug wires, when I pushed it onto the spark plug at some time,
it pushed the metal ring back into the outer sleeve rather than sliding on the
plug electrode.
I had that
on and off several times, and never really noticed any difference. They boots slide onto the plug pretty
hard anyways. It wasn’t until I
measured the resistance of the plug wires, that I discovered the problem. I couldn’t even get the meter probe into
the boot far enough to reach the metal ring. I also couldn’t get the boot to even slide back on the plug
wire, back to the correct position, so I just replaced that wire. I didn’t re-check the spark to make
sure that it was no longer intermittent, but it starts normally again, so it
fixed the problem. My coils are
mounted very near to the plugs, and I used high quality silicone plug wires. They were for a corvette, as I recall,
and only about 6-8 inches long.
Steve Brooks
-----Original
Message-----
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net]On Behalf
Of Al Gietzen
Sent: Thursday, January 03, 2008
2:19 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Weak Spark
All
this talk of weak spark got me thinking again about my 20B. It has the stock
CAS. I have found that the spark is weak and sometimes intermittent when
cranking. When I noted this, I was sure something was wrong. I then
checked using the Mode 8, and the spark was great. It would start and run, so I
forgot about it. The engine always started and runs fine, but I have noticed
more recently on cold mornings (meaning about 40F here in SoCal) that the
starting was a little more hesitant, and would fire intermittently for a bit
before getting going.
I
recall when we were checking timing on the dyno, it would not fire the timing
light consistently – figured it was the light. On recent flights, on two
occasions, after steady cruise for ½ hour or so; there was a very short
duration power sag; just a second or two and then back to normal. No
roughness; just some power loss that gets your attention, and then it’s
OK. I’m burning unleaded mogas, so shouldn’t be the famous S.A.G. others
have experienced. I have no explanation.
These
things, taken together, make me wonder if I’m really getting the strong spark I
should be getting. I know that during cranking it is barely enough to
fire the plugs. I haven’t checked it when running cuz it’s a little
difficult to hold a wire off and see how far the spark will jump when that prop
is going right there. But I guess I need to make a check of that.
What
sort of cranking spark should be expected? Other ideas on what to check? Is it
something about the EC2 and the CAS?
Al
Subject:
[FlyRotary] flooding
I made
it out to the airport today, soldered up the CAS and installed it. Before
I cranked it over, I put it in mode 8 and fired it off. The usual nice
blue sparks. Then set it to mode 0 and cranked with the plugs out and
pumps/inj off. No spark. Cranked and looked again. Every so
often there would be a weak spark or 3, but most of the time, nothing. So
little or no spark