I have a Rans S-6-ES Coyote II, the engine is a Rotax 912 ULS 2002.  Airframe and engine 177 hrs.my problem is 400 rpm loss when I shut off lane b

new spark plugs gap .024. New resistor caps. New wires. Pulled 6 and 4 pin plugs apart and took each individual wire out of its socket, checked for contact 

with the opposite wire. Lightly pulled on wires checking for broken wires.  Continuity test between trigger coil were wire is soldered and its opposite end at 6 

pin connector. Cleaned all grounds at intake manifold and at module bolt. Pulled coils out and visually checked wires. Ohm each coil between the two 

primary leads, results were t1-t2 15.47 b3-b4 15.48 t3-t4 15.46 b1-b2 15.15. I made an inline spark tester and with my wife in left seat after sunset tested for 

spark. this is where I’m at a loss.the drop occurs when I shut off lane b or bottom so lane a or top spark plugs are the problem. Cyl 1 and 2 to appear to be 

normal in that I shut off A I lose spark top spark plugs and B I lose bottom spark. On cyl. 3 and 4 its opposite. I shut off A and I lose spark on bottom cyl. 3

and 4. B I lose spark on top cyl.3 and 4.i have checked for crossed spark plug wires numerous times all is good. With both mags on all spark plugs fire, 

carbs are balanced, runs smooth, no power loss, full rpm range. No starting issues hot or cold. Any input from those guys and gals that never sleep at nights thinking about this stuff would greatly be appreciated







  • Re: 912 excessive RPM drop on lane A

    by » 8 months ago

    Have you measured resistance from plug cap to plug cap should be about 15K ohms. Each high voltage coil feeds two plugs so it is in series from plug cap to plug cap. The top front left and right ignition components are in series, top rear in series and the bottom the same. If you do not measure about 15K ohms on each trim the plug wires back about 1/4" to expose newer non corroded wire then apply electrical grease to preserve the connection before reinstalling plug caps and wires in coils.


  • Re: 912 excessive RPM drop on lane A

    by » 8 months ago

    I tested the old set of caps and wires they were OK. They were 20 years old the wires were so I put new spark plug wire and resistor caps on but probably Wouldn’t hurt to retest. I’ll do it now Thanks 

  • Re: 912 excessive RPM drop on lane A

    by » 8 months ago

    The test on my first post was the resistance on secondary ht leads with old wire and resistor caps.i put new wire and caps on and here are the readings between resistor caps T1-T2 15.14 T3-T4 15.47 B1-B2 15.91 B3-B4 15.20

  • Re: 912 excessive RPM drop on lane A

    by » 8 months ago

    I don’t know if i tested the primary side of the coils correctly. I put my meter leads on the two primary coil wires of a single coil at the 6 pin connector. For example 1T-2T. All 4 coils read .2-.3k ohms. Is that the correct way to test the coils?

  • Re: 912 excessive RPM drop on lane A

    by » 8 months ago

    Yes, it's best to test at the connector.

    You could try swapping the modules and see if the rpm drop follows the module.


    912/914 wire resistance checks


    AC volts from Internal generator----------------------Yellow to ground------18-20 ACVolts (With engine running, set multimeter to AC volts)

    *Suspect wire or ground problems if Charging coil (on stator) red to ground is more than 4.0 Ohms. Wiggle red wire during test (broken wire?) and check grounds on stator (2 ring terminals connecting to stator mounting screws)

    *Voltage (approx) from Red wires: 300rpm-7v (start-up RPM). 500rpm-12v. 1000rpm-20v, 2000rpm-40v, 3000rpm-60v, 4000rpm-80v, 5000rpm-100v.

    (With engine running, set multimeter to AC volts)

    **Do not test CDI modules with a multimeter. The voltage from the Ohmmeter can damage the integrated circuits

You do not have permissions to reply to this topic.