914UL mag drop
in General Tech Discussion
12 years ago
Hello, after 3 months of hangar, I tried to restart my 914UL equipped Europa XS. I found that the mag drop at run-up was lower than usual (at least that I remember). My engine has 350 hours with fully renewed carbs last Aug and 4 pins black boxes. At 4000RPM, I got a drop of 300RPM on A and a drop of 400RPM on B. I always had a slightly lower drop on one mag than the other one. But this time, I found it a bit too much and the engine was clearly running rough on mag B.
So I already went through the following items:
- sparks plugs have been changed about 50 hours ago, but changing these is next on my list.
Checking these, I found that the bottom spark plugs on cylinder 1 is having the color depicted under:
http://www.rotax-owner.com/rotax-blog/item/7-the-basics-on-my-spark-plugs -> This plug is oiled fouled, caused by poor oil control.
The top one also has a strange color but more velvet than black
So I really suspect that my issue is located with cylinder 1
- swapped the position of the charging coils (red cable coming from the back of the engine to the black boxes), same mag is dropping, so no issue there
- swapped the pick-up coils connectors (4 pins). Then, instead of having a drop of 300/400 at 4000RPM, I got a drop of 200/600. But on the same map, so seems that the pick-up coils are OK. But the difference in drop is extremely strange...
- check the resistor between top 1/2, top 3/4, bottom 1/2 and bottom 3/4 spark connectors and I got everything between 15.5kohm and 16.7kohms. So seems no issue here.
I well saw that some of the spark plugs connectors were not always giving perfect contact with the multimeter pins.
Next steps means removing the black boxes. But I first wanted to change the spar plugs before disassembling too much.
And the fact that I got totally different drops when swapping the pick-up coils to the black boxes gave me the idea that potentially the original pick-up coils connections to the black boxes could be wrong. The builder and first owner of the aircraft had some issues with ignition and I wouldn't be surprised that he switched the connectors of these pick up coils to the black boxes.
I was thinking of checking all connections from the stator to the spark plugs but that will mean removing the black boxes. And before I do that, I wanted to hear your thoughts on this issue.
I was also thinking of getting a stroboscope to make the measurements of sections 3.9 and 3.10 of the heavy maintenance manual, but I have to admit that I don't really understand how to practically measure the cut-in speed and the transition from start to operation timing.
Thanks, Jacques.
So I already went through the following items:
- sparks plugs have been changed about 50 hours ago, but changing these is next on my list.
Checking these, I found that the bottom spark plugs on cylinder 1 is having the color depicted under:
http://www.rotax-owner.com/rotax-blog/item/7-the-basics-on-my-spark-plugs -> This plug is oiled fouled, caused by poor oil control.
The top one also has a strange color but more velvet than black
So I really suspect that my issue is located with cylinder 1
- swapped the position of the charging coils (red cable coming from the back of the engine to the black boxes), same mag is dropping, so no issue there
- swapped the pick-up coils connectors (4 pins). Then, instead of having a drop of 300/400 at 4000RPM, I got a drop of 200/600. But on the same map, so seems that the pick-up coils are OK. But the difference in drop is extremely strange...
- check the resistor between top 1/2, top 3/4, bottom 1/2 and bottom 3/4 spark connectors and I got everything between 15.5kohm and 16.7kohms. So seems no issue here.
I well saw that some of the spark plugs connectors were not always giving perfect contact with the multimeter pins.
Next steps means removing the black boxes. But I first wanted to change the spar plugs before disassembling too much.
And the fact that I got totally different drops when swapping the pick-up coils to the black boxes gave me the idea that potentially the original pick-up coils connections to the black boxes could be wrong. The builder and first owner of the aircraft had some issues with ignition and I wouldn't be surprised that he switched the connectors of these pick up coils to the black boxes.
I was thinking of checking all connections from the stator to the spark plugs but that will mean removing the black boxes. And before I do that, I wanted to hear your thoughts on this issue.
I was also thinking of getting a stroboscope to make the measurements of sections 3.9 and 3.10 of the heavy maintenance manual, but I have to admit that I don't really understand how to practically measure the cut-in speed and the transition from start to operation timing.
Thanks, Jacques.
