912 ULS starting but stalls

Each module has two circuits. The main one fires the plug 26 deg before top dead center. The starter circuit shifts the timing of the main circuit to fire later, in one of two ways:

1) the old unit start circuits kick in to shift timing to 4 deg BTDC based on reading a low rpm. As soon as it reaches ~1200 (?) rpm, it "detaches", letting the timing revert to 26 degrees.

Because the start time is still BTDC, it's possible that the engine will fire backwards potentially destroying the sprag clutch. (Hence with these, it's best to, unlike a car, hold the start button down until the engine is truly running. As soon as the engine is turning faster than the starter the clutches harmlessly releases, so it doesn't hurt anything, but greatly reduces the odds of getting a damaging kickback.)

2) The new "soft start" modules have an extra wire run to the starter motor relay. When ~3V or more is applied to this wire, the start circuit wakes up for 15 seconds, retarding the timing to 3 deg *after* TDC. This makes a kickback very unlikely, but the engine runs like crap for those 15 seconds.

In both cases, the main 26 deg circuit will work in the running condition, even though the start circuit has failed.But in the starting condition, a dead start circuit will not trigger the main one and the plugs won't fire. If on "both", the remaining good mag will start the engine, using either the "L" or "R" set of plugs, but not all 8. When the retard function times out, you'll get all 8 again.

If all starts are done with both mags on, a failed start circuit on on may not be noticed until the second also fails.

I'm not the expert and writing this from memory, but the general idea is correct. I hope this is more clear.

Jeffry Stetson wrote:

Each module has two circuits. The main one fires the plug 26 deg before top dead center. The starter circuit shifts the timing of the main circuit to fire later, in one of two ways:

1) the old unit start circuits kick in to shift timing to 4 deg BTDC based on reading a low rpm. As soon as it reaches ~1200 (?) rpm, it "detaches", letting the timing revert to 26 degrees.

Because the start time is still BTDC, it's possible that the engine will fire backwards potentially destroying the sprag clutch. (Hence with these, it's best to, unlike a car, hold the start button down until the engine is truly running. As soon as the engine is turning faster than the starter the clutches harmlessly releases, so it doesn't hurt anything, but greatly reduces the odds of getting a damaging kickback.)

2) The new "soft start" modules have an extra wire run to the starter motor relay. When ~3V or more is applied to this wire, the start circuit wakes up for 15 seconds, retarding the timing to 3 deg *after* TDC. This makes a kickback very unlikely, but the engine runs like crap for those 15 seconds.

In both cases, the main 26 deg circuit will work in the running condition, even though the start circuit has failed.But in the starting condition, a dead start circuit will not trigger the main one and the plugs won't fire. If on "both", the remaining good mag will start the engine, using either the "L" or "R" set of plugs, but not all 8. When the retard function times out, you'll get all 8 again.

If all starts are done with both mags on, a failed start circuit on on may not be noticed until the second also fails.

I'm not the expert and writing this from memory, but the general idea is correct. I hope this is more clear.

Thank you.

That is a lot for me to fugure out. 

Today, it seems that it is not an electric problem.

See next post.

Jeffry Stetson wrote:

Each module has two circuits. The main one fires the plug 26 deg before top dead center. The starter circuit shifts the timing of the main circuit to fire later, in one of two ways:

1) the old unit start circuits kick in to shift timing to 4 deg BTDC based on reading a low rpm. As soon as it reaches ~1200 (?) rpm, it "detaches", letting the timing revert to 26 degrees.

Because the start time is still BTDC, it's possible that the engine will fire backwards potentially destroying the sprag clutch. (Hence with these, it's best to, unlike a car, hold the start button down until the engine is truly running. As soon as the engine is turning faster than the starter the clutches harmlessly releases, so it doesn't hurt anything, but greatly reduces the odds of getting a damaging kickback.)

2) The new "soft start" modules have an extra wire run to the starter motor relay. When ~3V or more is applied to this wire, the start circuit wakes up for 15 seconds, retarding the timing to 3 deg *after* TDC. This makes a kickback very unlikely, but the engine runs like crap for those 15 seconds.

In both cases, the main 26 deg circuit will work in the running condition, even though the start circuit has failed.But in the starting condition, a dead start circuit will not trigger the main one and the plugs won't fire. If on "both", the remaining good mag will start the engine, using either the "L" or "R" set of plugs, but not all 8. When the retard function times out, you'll get all 8 again.

If all starts are done with both mags on, a failed start circuit on on may not be noticed until the second also fails.

I'm not the expert and writing this from memory, but the general idea is correct. I hope this is more clear.

I want to thank everybody for all the help.  I think I figured it out.

I decided to follow the path of 1/2 of my LSRM instuctor team, Brian Carpenter.  He said 90% of Rotax problems are corrected by figuring out what has been done to change it from stock configuration.  So I found what it was.

Remember me saying I have had two 200 hr services by Lockwood on my carbs?  😧  So. How it is supposed to go is the idle mixture screw is assembled and tightened down to bottom out.  Then reversed out 1 1/2 turns.  WELL, WELL. I found that one carb was fully tightened and the other was reversed out 3 (three) turns.  (multiple senarios come to my dirty mind on the "distraction" that resulted in this outcome.  I hope it was good for him! 🙈🙉🙊 

I am embaressed that I went so many diffferent directions without checking what I PAID FOR!  AGAIN!  I am such a schmuck.  Now I will lean on the other half of my LSRM instuctor team, Carol Carpenter and make the proper engine log entry. 😒

Well, that's not it. 🙁

Jeffrey,

"Recently (150hrs or so) it starts immidiately but slows and stalls before the carb moves into whatever happens inside that bumps up the RPM.  This has always taken ~3-4 seconds as far as I remember.  Now it cannot go that long and it stalls out.  After that it takes a lot of cranking and and a bit of throttle to get it going."

Note: "....the carb moves into whatever happens inside that bumps up the RPM." The carburettors are not responsible for the automatic increase in RPM - this is an ignition (modul) function.

Fuel

It would seem your float bowls containe sufficient fuel for a normal start - the only question is then the continued supply. The fact that you can eventually get the engine running, would suggest supply is not a problem.

There is still a possibility that the fuel enrichment circuit/choke, is not working properly. Carburettor engines require a rich fuel:air mix, for an easy start/initial run.

Ignition

The likly source of your problem - if you can borrow & fit, "known to be good", ignition modules to see if they start your engine normally, this will conclusively exclude or pinpoint any problem with your ignition.

😈