YAIP? (Yet Another Ignition Problem?)

[FastEddieB]

I flew on Saturday and the ROTAX 912 in my Sky Arrow performed perfectly.

 

But when I taxied in, I thought the engine was just a tiny bit rougher at idle than normal.

 

When I switched off the #1 ignition, it got quite rough. When I switched off the #2, it was much smoother.

 

I then ran it up to about 3,000 rpm and checked each and there was very little drop and no roughness.

 

Back at idle, running on #2 (#1 off) was still rough.

 

I just happened to have my GoPro running:

 

 

Kind of hard to see what I'm talking about - the tach is just to the left of the Garmin.

 

I'm supposed to fly to Indiana on Friday, weather permitting. My tentative plan is to run over to the airport and maybe start out by looking at, cleaning and gapping the plugs. Then, if that doesn't work, maybe take the SoftStart module out of the loop and see if that makes a difference.

 

(note: the SoftStart retards the spark on #2 when it senses starter solenoid voltage and is supposed to revert to normal timing a few seconds after that voltage is lost)

 

Any thought? Am I just zeroing in on ignition when it might be something else?

 

Would appreciate any advice.

 

Thanks!

[FlyingMonkey]

Maybe pull and inspect some plugs? The fact that it's only rough at low RPM would make me think it might be marginally fouled plugs.

[FastEddieB]

I said that was Plan A this afternoon when I head over to the airport.

 

Decowling the Sky Arrow is kind of a pain, but I haven't done it in a while and I can take a closer look at a lot of things with it off.

 

And the plugs will be first!

 

It's also feeling a little fall-like in the mountains, so it might be a good time to tighten up the plug gaps a air to their winter settings.

[FlyingMonkey]

Whoops sorry...got distracted by your video and didn't see the rest of the post.

[Doug G.]

Squirrel! (Have you seen the movie UP! ?) lol

[C ICEY]

I just went through an ignition troubleshoot. I used EGT to determine the cylinder that was misfiring, and learned to make just one change at a time.

 

I initially ruled out carbs with a mag test with choke pulled out part way, maybe Roger can detail that one.....

 

My initial problem was one bad (loose) spark plug boot, which I replaced, but at the same time I put in another plug, which turned out to be a bad plug for whatever reason. I swapped one problem with an identical one.

 

my penance for not doing this was to do a complicated swap of leads from the coils and stators, and to send my ignition units out to get tested.

they all tested normal, which brought me back to the cable and plug boot, and a swap back to the original plug.

 

good luck with the troubleshoot.

[FastEddieB]

Update:

 

The plane started instantly. As soon as it smoothed out, at about idle killed one ignition and then the other and the drops were identical.

 

Tried various rpm up to 3,000 with the same result.

 

Flew the plane for about 10 minutes. After taxiing in, did it again and now ignition two was again a tiny bit rougher, but not that much.

 

Decided not to futz with anything right now.

 

But I'm unclear - how could one carb having an iffy idle circuit cause differing rpm drop with different ignitions? Whichever ignition is chosen, each cylinder on each side still has a firing plug. Sure seems to me that would cause about the same drop with either ignition selected.

 

Right?

[FastEddieB]

My bowls are easy.

 

I'll look tomorrow.

 

But take an iffy idle jet on one side (cyls 1 & 3, let's say).

 

With ignition one firing, it would fire an upper plug in one and a lower plug in the other.

 

Switch to ignition two, and the opposite plug in each cylinder would fire, lower in one and upper in the other.

 

That is how it works, I assume.

 

It's not like ignition one fires one side and ignition two fires the other - then it would make perfect sense that when you switched to the side with the bad idle jet it would drop more.

 

So, why would one ignition have a larger drop than the other?

[FredG]

"But I'm unclear - how could one carb having an iffy idle circuit cause differing rpm drop with different ignitions? Whichever ignition is chosen, each cylinder on each side still has a firing plug. Sure seems to me that would cause about the same drop with either ignition selected."

 

Eddie asked a very good question. The carbs don't change when you switch ignition circuits. How can it be a carb problem affecting rpm and running smoothness when the problem occurs when changing from one ignition to the other?

[FlyingMonkey]

Squirrel! (Have you seen the movie UP! ?) lol

 

Actually my wife says that exact thing ("squirrel") all the time...I am...um...distractable.

[FlyingMonkey]

Are mere mortals allowed to pull carb bowls, or just mechanics and ELSA owners?

[FastEddieB]

If its fuel, why does it consistently drop a bit more when I go to ignition 2, and idle perfectly smoothly with both ignitions on, even at idle? Seems like a clogged idle jet would manifest itself regardless of ignition switch positions.

 

Not arguing - I've had crud in my bowls before, so I'm clear on that concept, and that and the plugs are easy enough to check tomorrow.

 

Just trying to understand.

[FastEddieB]

And Andy - always invited to come up tomorrow and lend a hand!

[FastEddieB]

I'll report what I find tomorrow.

[FlyingMonkey]

And Andy - always invited to come up tomorrow and lend a hand!

 

I would love to Eddie, but I'm not a retired layabout like you and others on this board, I have to keep working to feed the CT.

 

Let me know when you are back from your trip though, I'd like to get together and compare notes on our babies.

[Tom Baker]

When you have a border line lean mixture just the difference in the ignition pattern from top or bottom plug firing can cause the results to be different. I was taught years ago when leaning an airplane without an EGT to check the mags, and if it was rough on one or both mags you are too lean.

[Ed Cesnalis]

When you have a boarder line lean mixture just the difference in the ignition pattern from top or bottom plug firing can cause the results to be different. I was taught years ago when leaning in an airplane without an EGT to check the mags, and if it was rough on one or both mags you are to lean.

• you are [need] to lean
  
• you are to [too] lean
  

[Jim Meade]

Well, Charlie, you should have got "boarder" vic "border" while you were at it.

 

I guess Tom's old teacher was assuming the plugs were not placed identically in relationship to the intake valve, otherwise it would seem to me they would act the same.

 

BTW, in one of the references I cited in a recent post, it said that even the plug gap orientation could make as much as 1% difference in power output. To us that is nothing but if you are spending hundreds of thousands of dollars on a racing engine than 1% may be a lot.

[Tom Baker]

• you are [need] to lean
  
• you are to [too] lean
  

 

Send me your phone number. Next time I want to post I will call and dictate my message, so you can type it for me.

I fixed it just for you!

[Ed Cesnalis]

I'm not giving you a hard time Tom, I just don't know how to interpret your post.

 

I'm the worst offender here.

[FastEddieB]

Headed over to the airport...

 

But first, some thoughts:

 

I will stipulate that Roger has at least one order of magnitude more experience with Rotax engines than I do. Possibly two!

 

So, his experience is highly valued here and I take it very seriously.

 

Hence, his take that my slightly higher drop on ignition two than ignition one being caused by carb problems will have me pulling my float bowls - probably not a bad idea since the last time was about seven months ago and it never hurts to take a look.

 

And I fully understand how Roger, after troubleshooting a hundred or more rough running engines and having it turn out to be carb related, would make that first assumption and usually end up being right.

 

But...

 

In Zen, there's something called "beginner's mind". Sometimes someone with less experience can see solutions that a more experienced person might not, not being "primed" to go in any one direction, as it were.

 

And then there's the old scientific method.

 

It still seems to me that a bad carb on one side would not favor one ignition over the other - or at least it has not yet been explained to me how.

 

And I'm not sure I accept Roger's assumption that an ignition problem would have to manifest itself equally at all rpm. I've seen ignition problems that were present at idle that went away at higher rpm, and some that idled just fine but broke down at higher rpm. Added to the mix is my SoftStart module that is supposed to retard the #2 ignition timing under one set of circumstances (12v at the starter solenoid) and then advance the ignition timing back to normal after the 12v is no longer sensed. Hence, maybe the drop I'm seeing at and around idle is due to the SoftStart keeping the timing retarded when it should not be.

 

In any case, my plan is to check, clean and gap the plugs, check the float bowls and jets (at least visually) and maybe check the SoftStart connectors and hit them with some Stabilant22™ for good measure.

 

I'll report what I find this afternoon.

 

And this discussion is NEVER meant to be argumentative or confrontational - I'm always open to new ideas and can only learn by questioning my preconceived notions and thought patterns.

[FastEddieB]

Roger,

 

I do appreciate all the help.

 

Basically spent most of the day bonding with my Sky Arrow.

 

1) I need to decowl on a more regular basis. I found the strap supporting my coolant tank had broken:

 

 

Took the broken strap to a homebuilder friend's house and we fabricated another.

 

Also found the plug cap for the lower Cyl 2 plug was very loose and one of the drain hoses from one of the drip trays was split at the nipple.

 

2) In any case, the plugs looked fine.

 

 

I checked them and they were all at .024", which I think is the winter setting anyway. Cleaned them up and reinstalled with fresh paste (for Andy's benefit):

 

 

3) Pulled both float bowls and they had tiny flecks of something, but nothing that I think would block anything:

 

 

 

 

The jets in the bowls (that's the idle jet, right?) were both clear and the two jets in each carb appeared clear looking at them with a bright light and a mirror.

 

Confirmed that the "choke" levers were against the pins both at full and zero control movement - that one has bit me before.

 

Anyway, buttoned everything up and it started right away with no leaks.

 

Still, she still seems just a bit rougher on ignition two alone than ignition one alone. But both at 1800 and 2000 rpm the drop was 200 for both, but with more roughness/vibration on ignition 2. At higher rpm, still fine.

 

Anyway, I'm satisfied for now its nothing major. Maybe play with it more later, maybe taking the SoftStart module out of the circuit to see what happens.

 

In any case, feel confident enough to fly to Indiana tomorrow to meet up with Karen. I'll advise how it goes (unless the weather is much worse than forecast tomorrow).

[FastEddieB]

First, I don't have a set of gauges - probably need to get some. What do you recommend?

 

Second...

 

Yesterday, all loaded up and ready to roll to Indiana, I taxied out, did a runup and began my takeoff roll...

 

My three "on the roll" checks are "Canopy - LATCHED", "Airspeed - ALIVE", and "RPM - 5,200".

 

Unfortunately, the power felt "soft" and I was only getting about 4,500 rpm. Aborted the takeoff, and could not get static rpm above about 4,500 rpm.

 

Taxied in, and with the help of a friend decowled, checked the plug wires (one did go on with a couple more clicks), and pulled the float bowls. They looked fine, with the exception of a tiny bit of clear silicone looking fleck sitting on the surface of the main jet of my right carb. Not blocking it, just sitting on it. Other jets looked clear.

 

Put the bowls back on, started up an "VIOLA!" - better than 5,000 rpm static runup.

 

At this point unsure what caused the prior problem. Had that fleck blocked the main jet, I would have suspected more than a smooth power loss on takeoff. I did not see any problem with the way the float bowls and floats were installed.

 

Weird.

 

In any case, plane did fine on the subsequent takeoff and on the two roughly two hour legs to Indiana, where I am now.

 

As an aside, at my next annual in March I do plan on overhauling my Bings, which are original from 2007, so it's about time.

[FastEddieB]

Just to let everyone know I made it to Indiana and back, arriving home about an hour ago.

 

Not a hiccup from the ROTAX, full 5,200+ rpm on every takeoff.

 

Details and photos to follow.