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Recently, the trusty 912S in my 701 has been, well, not that trusty. The symptoms started subtly about a year ago, with slight difficulty starting. Used to be, you couldn't count the blades before the thing sprang to life. Now I was counting 6 or 10 seconds, and having to mess with various combinations of throttle and choke - probably because the lack of immediate start was causing flooding.
Anyway, I had an annual inspection coming up, and even though I have my repairman certificate, I like to have a "real" A&P do the inspection every 2 or 3 years. So I describe the problem, and Shayne helpfully checks the carb floats and the jets - and there was indeed some dirt stuck in one of the starting jets.
The problem seemed to get a bit better, but within a few flights it's apparent there's still something wrong. It's now taking several cranks to start (from cold - seems OK from hot).
By now I'm getting nervous about flying, even though it's never given the slightest hiccup once running. So I decide to take it over to Sebring for a full diagnosis. But - you guessed it - the day I decide to take it, it won't start!
Shayne does some remote troubleshooting and wonders if perhaps the ignition modules have failed. He explains that they often fail progressively, so that the RPM at which the engine will start slowly increases, until the starter motor simply can't crank the engine fast enough.
He asks me to check the ignition by hooking up an induction timer. I don't have one, but Amazon does; 2 days and $30 later, so do I.
I hook it up, tie the aircraft down, and crank away. No flashing light - nothing. I think - Shayne was right, it was the ignition modules!
But new ones aren't cheap - about $2k for a pair - and I want to be sure before I order them. So I decide to check the induction timer on another engine. After all, I've never actually seen this thing work. So I pop the hood on my Jeep Wrangler, and do you think I could find the HT leads? Nope. On older vehicles I could identify every component under the hood. These days, not so much. I remove the "JEEP" branded plastic sitting on top of the V6, thinking surely the HT leads would be visible after that. But nothing looks remotely like a spark plug or an HT lead!
Getting a bit frustrated, I look across the garage at my wife's Tesla Model S. No help there! How about a mower, I hear you ask. Nope. Our old mower died a year ago, and we went electric there too - a Ryobi 38" ride-on gadget which is by far the best mower we've ever had. No gas, no oil, no belts, no hydraulics - just a motor for drive and two more on the deck powering the blades - and so QUIET! But I digress...
I recall we do still have another gas engine - a little 5kW generator. We live in Florida, after all. I start the bugger, and clip on the induction timer. Nothing. No flashing lights. And I know there's a spark - the engine's running!
So back it goes to Amazon and this time, instead of ordering something for $30 from a manufacturer I cannot pronounce, I order a Bosch for $60. Last I checked, those chaps know a thing or two about electrical stuff. It arrives, and first thing of course is to test it on the generator. There it is! A nice steady flash-flash-flash. Back to the Rotax, clip it on, crank away, and nothing. So, they had failed. Looks like I will have to shell out the $2k.
Quickly checking in with Shayne, he says "not so fast" on ordering the official Rotax parts. He points me to a Czech outfit (https://www.ignitech.cz/en/vyrobky/bikes/rotax/rotax%20912%20and%20...) who do a replacement for the OEM units (which I believe is a Ducati unit anyway). Here's the good news - the replacement units are about $300 for the pair. That's a lot better than $2k.
I order a pair, with the optional longer harness so I can mount the new units on the firewall, away from the heat and vibration the original units must have suffered mounted right on top of the engine.
The extended harness plugs right in to where the old units did:
Holding my breath, I crank the engine, and - we have ignition. The engine literally bursts into life within a microsecond of cranking the starter. Naturally, I do plenty of ground tests before returning to service and going flying, but no problems so far. I will certainly let everyone know if the engine misses a beat...