Joe Linnebur

We just got done dealing with the same issue you’ve been dealing with, and it was after a mag overhaul. Many months later, my suggestions to replace the impulse coupling was taken and the problem fixed. The prop kickback is a good sign that maybe your IC spring is losing tension and not retarding the firing (ie. it’s snapping/spinning the mags through before TDC causing a cylinder to light off early and push it towards bottom dead center). Ours was inconsistent in starting issues initially, then became atrocious to start. You can YouTube some good vids like this. Basic, but a nice visual. If you watch this, the retarding occurs by the flyweight getting caught, and the flyweights are set to release at about Top dead center. The Spring tension then spins the mag through at a high rate of speed creating a usable spark for starting. So, if your spring tension is starting to wane, or internal wear in the coupling is letting that flyweight loose too early, you end up where you (and I) are at. Hope this helps.

I second this!

Just a follow-up to this for future answer seekers: We ended up replacing the impulse coupling. The spring tension was not adequate. Starting is back to norm. Thanks all for the ideas and experiences

Good info. I’ll pass this on to our A&P. Appreciate the insight

Yes, both capacitors, points, coils, etc.

Timed to 25 BTDC. That's kind of what I'm thinking right now is ignition switch issues. One idea for troubleshooting was starting it with the P-leads removed to see if that results in any difference.

It was a local facility. It's been removed and reinspected by our current IA (who overhauls these dual mags a lot) and he found everything put together correctly. We're thinking internally its looking solid. Once it starts, its 100% fine...its just getting it started.

Good evening everyone; I've looked over the previous posts regarding starting issues and I figured It'd be easier to just start a new thread with the issues we're having: Aircraft: 1979 M20J Engine: A3B6D - with a Bendix D3000 Dual mag (overhauled in April, and thats when these issues began) Impulse Coupling...it's not Shower of Sparks We overhauled the D3000 Dual mag in April because of a bad running mag. Overhaul worked out fine. After the overhaul, we noticed that the previous starting technique wasn't working so well. On the first attempt, the engine would only turn over, with no interest in even attempting to act like ignition was occurring. After a few more attempts, it usually would reluctantly start. Mag checks during the runup were always well within limits (less than 100 rpm drop, smooth running, etc) and never indicated any issue with either mag...it was just starting it was the issue. I've noticed that some starts occurred after running the starter and after 10 blades or so, bringing the key back to "both", only to have the engine actually come to life. This has happened on a number of my starts. There have been other starts where it turns over 10 blades, key off, back to "start" and then push and it starts after 2 blades. Up to now, I've been the only one to be able to start it, and there seems to be no consistency in any technique, so lets not go down that rabbit hole. We've tried multiple new techniques and there's no consistency at all. We originally though it was a flooding issue, but that's been determined that it was flooding due to the multiple start attempts. We recently had the mag pulled and re-inspected. No change. Its now with our main A&P. We discussed checking the ignition switch and if its grounding out the entire mag while in the start position. Based on my experience where it wouldn't fire until I selected "BOTH" seemed to be a possibility. He thought he may have found it intermittently grounding out the mag and "fixed" it, but I'm not sure "how" he did (I didn't have the conversation with him). Fast forward a day (today) and a partner was attempting to bring it home. Neither he or the mechanic could get it started. This was after he pulled the mag off and did another interior check of the components. I have noticed that when I run the prop through, looking at the 25 degree and TDC marking on the starter ring gear assembly, the impulse coupling tends to actuate well past the TDC position (about 3-4 teeth on the gear, plus or minus a couple. math tells me about 2-3 degrees past TDC). I'm not sure if our impulse coupler is actuating too late in the piston movement process thus making it a bear to start. #atmywitsendhere Have any of you all run into a scenario such as this where it was obviously ignition related, yet completely baffled you as well as your mechanic? Ours is baffled at this point. I'm about to recommend replacing the ignition switch based on previous posts as it seems like the mag is grounding out when in the "start" position intermittently. Any feedback on past experiences would be greatly appreciated to push us in the right direction. Thanks everyone

That’s weird, our ‘79 had the dual mags overhauled recently as well and I’m seeing the same thing.

We had this same issue. In the annual, they “cleaned the probe” and now it’s solid. Start easy and work from there maybe?

I’ve got a Teslong as well. I too would recommend it.

Just some weather issues to consider: winds aloft over the Rockies in the winter tend to go up in the winter months. 20+ knots flowing over the rocks can make for lengthy moderate/severe turbulence over the route. Mountain waves can create downdrafts in excess of your aircraft’s performance, and if flying higher, your performance will already be limited. Flying directly over the big stuff should only be done if all stars align (perfect weather, perfect craft) and even then always have a plan B and C. Dealing with a severe up/downdrafts when you’re only a few thousand feet agl is not worth any time saved. Go around the stuff As for IFR, steer clear in the winter of visible moisture. There are lots of stories of people who flew here who had never dealt with this type of flying and subsequently either lost their life or got really close.

Yea, it’ll get drained when the time comes. I was having difficulty “seeing” how the gasket gets seated but my brain finally understands. Remove wire, remove screws, pull entire unit out of tank through the inspection panel, remove old gasket/clean mating surface, install gasket, re-install unit, screws/torque, etc. I’m a task card kinda person. Thanks for the feedback

Sorry to revive this thread, but a quick question on replacing the gasket for the outboard sender. After pulling the inspection panel, it’s obvious that the gasket needs replacing (finally, an answer). When the 5 screws are removed (after removing the wire connector in the middle), does the actual indicating unit in the fuel tank remain attached and in-place, or does it require to be held in position during this process? Id prefer not to assume when we start going through the replacement process. Thanks for any feedback

Consider this option. In the process myself of putting something like this together: