Run-Up Mag Drop?

[danbenua]

I'm test flying a new IO-540 with one LSE Plasma-III and
one Mag. During run-up, turning off the mag produces a
30 RPM drop, but turning off the Lightspeed causes the
RPM to drop by over 200. I expected a difference because
the LSE produces a hotter spark and its timing is adjusted
for reduced manifold pressure, but does this seem right?
I would appreciate input from others running a similar
asymetrical ignition system.
Thanks!
- Dan
RV-10
8 hrs.

[Mel]

200 RPM is pretty excessive. I would check out all aspects of the mag.

[breister]

I had a similar setup on my previous plane. The drop was around 150 for the "Mag ON" scenario. Checked the mag, it worked fine. Mag off drop was almost unnoticeable.

I attributed it to the Lightspeed causing the RPMs to be higher than two Mags would have been.

I only had a Lightspeed II (not even a II plus). But, 200 may be too much. I agree with the previous poster, check your mag.

[AlexPeterson]

Your rpm drop might be normal, given the huge difference in timing/duration/intensity between the two at runup MP's. Talk to Klaus if you don't get an answer here as to what is typical. But, many are running one EI and one mag, and someone will have the answer. Relative smoothness should count for a lot.

You'll want to, at appropriate altitudes/locations, turn them each off in flight to get an idea of their respective contributions for in-flight power conditions as well. I have concerns that an in-flight failure of one of my ignitions will not be noticed, as will you if your mag stops working. I only notice it when well LOP (I have two Plasma III's).

[victor]

Is your vacuum line hooked up to the Lightspeed? If not, your timing will be retarded several deg. on the Lightspeed, and will not run to specs.

[db1yg]

Hi Dan,

I have an Eci 0360 with a Lightspeed PIII on the right side and a Slick mag on the left. At run up when I do the ign check I always get a 10 or sometimes 20 rpm drop with the mag off and a 60-70 rpm drop with the Lightspeed off. The timing on both was just checked at my annual condition inspection.

A 200 rpm drop sounds excessive--you might want to call Klaus--be prepared for his--how do I say this-- "personality"!!

Cheers,

db

[N131RV]

Causes of mag drop vary widely (and wildly). From what you describe, it definitely sounds like a problem with the standard (non electronic) ignition side of your setup.

Troubleshooting such a problem is usually simple. Start with the basics. Ensure that all plugs on the mag are in good condition using a plug tester. Inspect all plug leads and connections thoroughly. Ensure the timing is correct.

If that does not fix it,then it may be a problem internal to the mag. Mags differ in construction details (slick vs bendix), but I have experienced mag problems relating to improper assembly, worn points, worn breaker cam, etc. The only cure is removal and inspection/rebuild of the mag. You stated it's a new mag, so my money is on a bad plug or the mag timing. Just a WAG.

Thats about all I can offer,
JP

Originally Posted by danbenua

I'm test flying a new IO-540 with one LSE Plasma-III and
one Mag. During run-up, turning off the mag produces a
30 RPM drop, but turning off the Lightspeed causes the
RPM to drop by over 200. I expected a difference because
the LSE produces a hotter spark and its timing is adjusted
for reduced manifold pressure, but does this seem right?
I would appreciate input from others running a similar
asymetrical ignition system.
Thanks!
- Dan
RV-10
8 hrs.

[zav6a]

I have two electronic ignitions. The advance module is powered with one of the units.

When the unit without the advance module attached is shut down - limited RPM drop ( 25 to 75 RPM, depends on how far it is leaned, much more drop with leaner mixture).

When the unit that shares power with the ignition advance is killed, a much larger drop is experienced (100 to 300 rpm - again depending on how far it is leaned.

Note that my runup rpm results in a full 25 degrees advance, without any additional advance from the vacuum module.

Moral of the story, a differential in the rpm drop has almost nothing to do with the source of spark (note that mine are identical and I get a huge differential). . It has a lot to do with advance. The magnitude of the drop is also dependent on mixture.

I do runups at a consistent fixed fuel flow and RPM - much more meaningful.

[Guy Prevost]

Was there any resolution to this question? I have a similar setup, 1 slick mag, 1 Lightspeed ignition, light CS prop. I've always seen about a 40 RPM drop when I shut the mag off and about 160 when I shut off the electronic ignition. Now that summer temperatures are driving the density altitude at my home airport towards 8000', I'm seeing a 200RPM drop when I shut the Lightspeed off. Obviously if I had 2 mags I would have reason to be concerned. I'm not so sure about my current setup....

[Kevin Horton]

Originally Posted by danbenua

I'm test flying a new IO-540 with one LSE Plasma-III and
one Mag. During run-up, turning off the mag produces a
30 RPM drop, but turning off the Lightspeed causes the
RPM to drop by over 200. I expected a difference because
the LSE produces a hotter spark and its timing is adjusted
for reduced manifold pressure, but does this seem right?
I would appreciate input from others running a similar
asymetrical ignition system.

As others have said, the over 200 mag drop when selecting EI off sounds excessive. I've got one LSI EI and one mag. I see around 150 drop when selecting the EI off.

For troubleshooting, it might be interesting to disconnect the manifold pressure input to the EI. Plug the end of the line that goes to the engine, so you don't have a vacuum leak.

Now the EI will think you are at full throttle, and it won't advance the spark, so it should fire at the timing angle, which should be the same as when the mag fires. With both mag and EI firing at the same angle, you should have similar mag drops on each. If not, that may point to one or both being timed wrong, or possibly some weakness with the mag.