English French German Italian Portuguese Spanish Swedish

rotax brp

 

Mag drop

  • james geyman
  • james geyman's Avatar Topic Author
  • Offline
  • Fresh Boarder
  • Fresh Boarder
More
4 months 1 week ago #16514 by james geyman
james geyman created the topic: Mag drop
Hello everyone,

I fly a Vans RV-12 with the 912 uls engine, 2009 vintage with 350 hours. The Mag drops seem excessive at 160 A ignition and 270 B ignition. I changed the oil, spark plugs, had the carbs overhauled and synched. All spark plug caps (ngk connectors) read at 4.6 kohms resistance (normal) so I am not sure what is causing the 'mag' drop. It runs rough still on the B CDI 'mag' circuit. ? Is this a dirty air filter issue
? Is this a stator coil trigger pickup issue
? could it be a focal CYLINDER problem ( I saw trace oiliness on cylinder 2 spark plugs of last change) - is a compression check in order (it was fine 8 months ago by hx)

The ignition harness seems intact but I haven'the tested each plug wire. It is hard to find a rotax specialist in Denver. Please help.

Please Log in or Create an account to join the conversation.

  • james geyman
  • james geyman's Avatar Topic Author
  • Offline
  • Fresh Boarder
  • Fresh Boarder
More
4 months 1 week ago #16531 by james geyman
james geyman replied the topic: Mag drop
update: changed out spark plugs again with new NGK caps; re-synched engine at 3000 rpm; still mag drop ignition A of 200 and ignition B of 300 with roughness on later.
afraid to fly it. reviewed last 9 yrs of annuals: always just 100 mag drop A and B circuits. Just had carbs overhauled/inspected at Lockwood. Told me they keep the needle jet at owners/prior placement; which I never touched. Called builder of my Vans RV-12 and he suggested checking spark plug firing by firing up engine on Ignition A and touching all four exhaust pipes; instead will get inductive timing light to see if each spark plug is firing. Suspect electrical system problem still. Will ask my A & P to check ignition wiring for hidden/occult wire break, especially if get missing spark plug firing on individual testing. Hopefully it won't be a coil (transformer) problem, or module (capacitor) problem; or heaven help me a stator/trigger coil gap problem. I am just the owner and not qualified to take the engine apart.

Please Log in or Create an account to join the conversation.

More
4 months 6 days ago #16538 by Peter Kl.
Peter Kl. replied the topic: Mag drop
Hi James,
Exchanging the caps made the mag drop worse. That makes me guess that a thorough check of the spark plug wiring makes perfect sense. No. 1, to change the plugs you had to fiddle about with the wires which can make the effect of a broken wire worse
No. 2, not replacing the wires can deteriorate the connection between new cap and wire which may or may not explain the bigger mag drop
If I may suggest you take off the new caps and cut back the wires by 1/2 inch and screw the caps back in place. Allow a little drop of silicon on the outer surface of the wires so the caps can be screwed on easier (less friction between rubber of cap and wire; also you can safely tell when they really are in place).
It's a little effort at no cost. Plus, it can be done by non-scientists like us.
Good luck.

Please Log in or Create an account to join the conversation.

  • james geyman
  • james geyman's Avatar Topic Author
  • Offline
  • Fresh Boarder
  • Fresh Boarder
More
4 months 6 days ago #16544 by james geyman
james geyman replied the topic: Mag drop
Thanks Peter so much for the advice. I went out today and tested the engine running on ignition A and all four exhaust pipes measured about the same temperature; then repeated the same on ignition B (on RPM of only 2200), so I think the bad ignition/plug idea is wrong.

It is probably something more overt and simple, such as a bad synch job or carburetor issues. I just got the carbs back from Lockwood Aviation in Florida for their overhaul, but maybe something is still amiss. I still get RPM drops at runup at 4,000 of 200 ignition A and 300 ignition B, so a single spark plug or broken wire would not affect both ignition circuits.

tomorrow I will check the carb floats again (I did have a sunken float several weeks ago), and the carb vent tubes (will take them out of the hanger which crimps them a little bit; wondering if this restricts the carb float chamber pressure equalization at working engine RPM).

I will keep you posted. My local A&P gets a look at it later this week; but again he rarely works on a rotax engine.

James

Please Log in or Create an account to join the conversation.

  • james geyman
  • james geyman's Avatar Topic Author
  • Offline
  • Fresh Boarder
  • Fresh Boarder
More
4 months 5 days ago #16546 by james geyman
james geyman replied the topic: Mag drop
Today I checked both float bowls; they were pristine and had no debri. all four floats weighed between 3 gm and 3.1 gm each; so were all in spec. I synched again at 2500 RPM. I am still getting A mag drop of 160 and B mag drop of 270. This is within Rotaxes spec drops of 120 diff and 300 max so I will just live with it. I pulled the choke during the mag check and it dropped another 300 rpm and really sputtered so I think it is more a summertime in Denver problem of just the Bing carbs running rich at altitude. I heard they are not really altitude adjusting and likely just are running rich. My airport is 6000 feet AGL and in summer the density altitude is 7,000 to 8,000 feet. I could probably adjust the needle jet setting but will just wait out the summer and fly the airplane. Maybe much ado about nothing.

James

Please Log in or Create an account to join the conversation.

  • james geyman
  • james geyman's Avatar Topic Author
  • Offline
  • Fresh Boarder
  • Fresh Boarder
More
3 months 4 weeks ago #16606 by james geyman
james geyman replied the topic: Mag drop
just a final update:

the mag drop dropped back to normal for me; at 150 rpm drop each (actually 130 and 160 a and b) after a better carb synch using a dual manifold helio gauge by an experienced a/p for the rotax; as well as setting the needle jet to the second setting; since i fly out of 5,000 feet msl with DA's of 7,000 to 8,000 feet in the summer. back to normal. so great.
The following user(s) said Thank You: RotaxOwner Admin

Please Log in or Create an account to join the conversation.