Igintion Issue

[Agfoxflyer]

I have a Series 5 with a 912ULS. A few weeks ago I ran up the engine and did ignition check. Ran fine with ignition A grounded out. Switched and ran real rough on A alone. It runs and sounds fine with both ignitions on. Mechanic has checked both ignition modules, and coils. I have checked all spark plug wires. Someone suggested it might be a bad connection on the ignition switch for A. Will check that out next time at airport. Question, if an ignition module is bad or going bad, does it run at all? Any other ideas would be appreciated. Need to go flying.

[kitfox2009]

I suggest VERY carefully checking the ground wires on both modules.

[Dave S]

I'd second the ground wire check. The original 912ULS has a separate ground wire for each module going to the intake manifold each held by a separate screw. I believe, where the manifolds are switched right to left to make room for the oil tank, on some S5s one of the mods with the manifold switch hooked both ground wires to a bracket and the bracket to the manifold with a single screw due to the shortness of the ground leads - basically combining the separate grounds through a single point. Might be worth a check on the module grounds. But - your mileage may vary.........could certainly be something else too....

[kitfoxnick]

I second the others advice. Breaks in the ground wires can be hard to find sometimes. I find the easiest way to find the culprit wire. Is to stick a sewing pin through the wire insulation on the coil ground wires, and measure reisestance with a multimeter.

[HighWing]

I have had similar symptoms on my 912 UL on cold start after sitting for a while. Then after changing plugs, all good again. My take is that my infrequent flying with Avgas to avoid the unleaded's degradation on sitting did a number on the plugs.

[Av8r3400]

Another thing that I have discovered. These ignition units are not very powerful. I gap my NGK plugs (per Hal Stockman's recommendation) to .020-.024". I have found their performance is better than the .028-.032" recommended by Rotax.

Be sure to at least check them before installing. I have seen new plugs with up to .040" gap in the box.

[Dave S]

Larry,

I have thought about smaller gaps for the plugs on the ULS; but, have always gapped mine at the tight end of the Rotax recommendation at 0.028".

Considering your experience with smaller gaps; have you observed this to be beneficial over the entire spectrum of operations? What have you noticed on specific conditions like cold start, low RPM, full power (I would think it would insure better ignition under WOT for sure) and ranges between idle and full power. Do you get better performance with our cold ambient temps up here in the northern tier?

I tend to reuse plugs that are in good shape; and, include a resistance test along with cleaning and visual evaluation - on occasion I have found a plug with infinite resistance under the meter which still fires well which indicates to me that the carbon resistor is cracked - those get tossed. I need to checking resistance on new plugs also - at least on other engines, new plugs are not always right I have found - hence my choice to reuse "road tested" ones if they are otherwise OK. Any thoughts on cleaning and reusing plugs from your experience?

[jrevens]

According to the maintenance manual for my 912 ULS, the gap is supposed to be .023 - .027".

[DesertFox4]

I used .023 to .024 for years with better results than the wider gapping. I did not have the high torque starter or soft start and the closer gap helped on starts on mornings with 50 degree temps or colder.
Also used 100% 100 LL Av Gas with Decalin additive and experienced no fowling between 100 hour plug changes.

[Av8r3400]

Dave - I found the engine to run smoother across the rpm spectrum. Cold starting seems to be easier, too.

I buy 8 new spark plugs every year. For $16, this is cheap maintenance. Cleaning and reusing these plugs isn't worth the effort, IMO.

[HighWing]

Another thing that I have discovered. These ignition units are not very powerful. I gap my NGK plugs (per Hal Stockman's recommendation) to .020-.024". I have found their performance is better than the .028-.032" recommended by Rotax.

Be sure to at least check them before installing. I have seen new plugs with up to .040" gap in the box.

This has been my practice since the early days. I can't remember why I went this way, but I am typically not an experimenter in things technical and so presume I heard it from some source - likely the early email lists. My climate is not as cold as some on the forum, but have camped overnight in sub freezing temps and flown in the Desert Southwest and have not had issues with cold starts, hot restarts or long periods between starts.

[kitfox2009]

Good evening folks. Hope everyone is staying away from each other and spending time in the Hanger or better yet,in the Air.
I just wanted to update my recent experience with a few modifications on my 24 year old 912 UL with close to 900 fairly trouble free hours. Over the past couple of years I have found when the hanger temp gets close to freezing the CDI modules do NOT provide enough juice to start the engine. My cure for this was to zip tie a "automotive battery blanket" over the modules and leave it plugged in all the time. About 50 watts power consumption.
I got concerned that if these CDI`s should fail in flight over our inhospitable terrain the outcome may not be good and started looking for alternatives to the 900USD (each) from Rotax dealers. I found a supplier in France who makes up CDI`s that come with enough cable to mount them remotely from the engine. Just last week I installed these in my Vixen. There is enough cable supplied to mount them on the cockpit side of the firewall! I have only used them a few hours,but so far it starts better than ever. Hopefully I won`t get a chance to try the COLD start for quite a few months!
I am not sure if I am allowed the state the company name in this forum. The price is about 50% lower than original equipment. I could PM it if anyone is interested.

The other modification was increasing the size of the balance tube. I have around 100 hours on this change and I believe the engine runs smoother through all RPM ranges. It is a 912UL with a 72 inch IFA IVO prop. Purchased on this forum to replace a 70 inch "high pitch" IVO I have used for the past 10 years or so.

Appreciate anyone`s questions or comments.

Cheers
Don

[DesertFox4]

Don, you can name that ignition module manufacturer. It may be of value to other members. 👍

[kitfox2009]

Good evening folks. Hope everyone is staying away from each other and spending time in the Hanger or better yet,in the Air.
I just wanted to update my recent experience with a few modifications on my 24 year old 912 UL with close to 900 fairly trouble free hours. Over the past couple of years I have found when the hanger temp gets close to freezing the CDI modules do NOT provide enough juice to start the engine. My cure for this was to zip tie a "automotive battery blanket" over the modules and leave it plugged in all the time. About 50 watts power consumption.
I got concerned that if these CDI`s should fail in flight over our inhospitable terrain the outcome may not be good and started looking for alternatives to the 900USD (each) from Rotax dealers. I found a supplier in France who makes up CDI`s that come with enough cable to mount them remotely from the engine. Just last week I installed these in my Vixen. There is enough cable supplied to mount them on the cockpit side of the firewall! I have only used them a few hours,but so far it starts better than ever. Hopefully I won`t get a chance to try the COLD start for quite a few months!
I am not sure if I am allowed the state the company name in this forum. The price is about 50% lower than original equipment. I could PM it if anyone is interested.

The other modification was increasing the size of the balance tube. I have around 100 hours on this change and I believe the engine runs smoother through all RPM ranges. It is a 912UL with a 72 inch IFA IVO prop. Purchased on this forum to replace a 70 inch "high pitch" IVO I have used for the past 10 years or so.

Appreciate anyone`s questions or comments.

Cheers
Don


Good morning again folks
Desert Fox4 has advised it is OK to name the CDI supplier. I have NO affiliation will them other than this one deal. Their representative is Eric. Website www.allumage-moto.fr phone 0033(0).81.55.23.39. Price is approximately 500USD.

I fabricated a small aluminum box and mounted them on the cockpit side of the firewall. There is sufficient wire to reach the old location on the engine. Simple installation. I have the older 4 wire connectors. If so, be careful with the single wire connections to get them right.
Good luck.
Cheers
Don