Large RPM drop

I have a magneto on one side and the Electroair ignition on the other. When I do my runup I notice a large RPM drop, in the range of 200 RPM from 1700, when I cut off the Electroair ignition. When I cut the magneto, much less of a drop but still over 100 RPM. Lycoming says up to 175 RPM drop is OK (with 2 magnetos). Engine seems to be running fine. Has anyone else noticed these large RPM drops with electronic ignition? It might be the Electroair has advanced timing at 1700 RPM that is the explanation.

If you are fuel injected, try leaning the mixture before doing the run-up and see what happens.
A rich mixture can cause a lot of mag drop. Sometimes electronic ign. is better able to fire the rich mixture......

Scott is dead on. the EI's will burn a much richer mixture than the mag, and it is much more noticeable as to HOW rich it is when you switch over to the mag. When doing your run up, first lean the mixture. You will notice an increase in the RPM's. Then do your checks and you will see a much smaller drop on each ignition system.

Vic

the 540 Electroair/mag plane I worked on experienced 40/100 rpm drops during proper leaned run ups. Other (4cyl) aircraft with various make EI/mag setups ranged from virtually zero EI rpm drop to about 75 rpm drops. The EI always triggering the engine better than the mag.

Bob, if you do the check at 1800 as per Lycoming, rather than 1700, the drop will be less.

My gut feeling is the plugs are dirty.

Fly for a half hour leaned out, it will be better.

bob888 said:

It might be the Electroair has advanced timing at 1700 RPM that is the explanation.

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It could. You could do an inflight check (WOT cruise @ 3000 ft or so) for 5 min on one and 5 min on the other and record CHT's. That would give you some indication of timing. Also, you would want to ensure that A/F is not out of the range of the mag.

Just make sure the fuel flow is constant.

BTW - This is not to override other comments, just a specific note on the timing aspect.

I just installed an Electroair in my -10. Did the first run up with the new ignition today. The left mag is on the lower plugs and the EI is on the upper plugs. I did it this way to keep the high energy, non shielded ignition leads away from the egt and chat small signal wires near the lower plugs.
The runup I did this afternoon with the engine full rich at 1800 RPM was around 20 rpm for the EI and 150 for the mags only. This was a quick check of the system and take the numbers with a grain of salt they are from memory. The idle was up from 750 rpm with dual mags, to 950 rpm with the single mag/ single EI. The advance as measured at idle was 39 degrees at around 14 inches. Once again, the numbers are from memory. I intend to record more accurate data this upcoming week. I'll post it afterwards.

I'm curious Bob, did you install the unit using the traditional key switch or two separate ignition switches, one for mag and one for EI?

Been Through This

I have O-320 with fuel injection, Slick on the left and Electroair
on the right. Started out with key switch. Un leaned I get 30 rpm drop
with Mag off and 110 drop with EI off. But before changing to toggle
switches had to worry about back fire. Electroair, even though they
have key switch install in manual, say toggles much better, and they
are right. Zero chance of back fire with toggles. I talked to them a couple
of weeks ago and asked, again, about the big drop and was assured all is well.
But, I always watch the EGTs also when doing the checks. Just want to
see all four cylinders making fire. Just me.

As a follow up to my previous post. During my second run up I after leaning, my mag drop at 1800 was 130 rpm for the mag and 10 for the EI.

Scott and Vic are right. I would add to lean aggressively during warmup and taxi. This will minimize plug fouling, which I bet you have. Check the bottom plugs.

These two ignitions are not firing with the same timing advance. The mag is fixed, the EI even at 1700 is at part throttle with low manifold pressure and will be running some advance over the the mag because of that lower MP.
You'll have to learn what is a normal drop for each side and use that reference.

Tim Andres

tim2542 said:

These two ignitions are not firing with the same timing advance. The mag is fixed, the EI even at 1700 is at part throttle with low manifold pressure and will be running some advance over the the mag because of that lower MP.
You'll have to learn what is a normal drop for each side and use that reference.

Tim Andres

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+1. I agree, I don't think the OP has any problem, it's running as I would expect.

I have an angle valve motor with Electroair on one side and a magneto on the other. I lean for taxi shortly after engine start. I perform my runup with the mixture still in the lean for taxi position. When switching off the Electroair ignition I get a 60-70RPM drop. When running the Electroair and switching off the magneto I do not see a noticeable RPM drop. I have the Electroair set up on the top plugs on one side and the bottom plugs on the other side.

Just my experience, for what it is worth. The Electroair has never skipped a beat, the magneto side has been less trouble free!

eaglen92ce said:

I have an angle valve motor with Electroair on one side and a magneto on the other. I lean for taxi shortly after engine start. I perform my runup with the mixture still in the lean for taxi position. When switching off the Electroair ignition I get a 60-70RPM drop. When running the Electroair and switching off the magneto I do not see a noticeable RPM drop. I have the Electroair set up on the top plugs on one side and the bottom plugs on the other side.

Just my experience, for what it is worth. The Electroair has never skipped a beat, the magneto side has been less trouble free!

Click to expand...

I had Electroair years ago in another airplane, liked its a lot but it did break a starter ring once on start kick back. Changed procedure to start on mag and no more broken start rings.

FWIT i now have EI from Robert Paisley and it too will kick back on start, use mag only for start.

Don't know why this is so except it seems once an engine spins up and EI is no longer firing at TDC, it will not go back to TDC fire unless power removed and system resets. Sometimes I get good start and then quick quit, probably due to inadequate priming, that's when EI will kick back on second start.