S3flyer Posted January 24, 2016 Report Share Posted January 24, 2016 Went flying today and all went well until I powered down after a 1.5hr flight. The engine started easy as always, ran smooth while idling and during the run-up. Continued to run smooth doing the module check with 100rpm drop for each module. Take off, flight and landing all fine. I powered down as I always do -- 1 module at a time - and when I was running at idle on the left module the engine was very rough. Going to both smoothed it out. I double checked by switching modules a few times and the engine clearly runs rough when idling on the left module. I didn't have time to do another run-up so plan on going out tomorrow and try some diagnosis. I have the new Rotax Advanced Modules. Thoughts on the cause and things to do to isolate the issue? Link to comment Share on other sites More sharing options...
Aero-Nut Posted January 24, 2016 Report Share Posted January 24, 2016 I had this happen on my 912 in my Kitfox. It could be various reasons related to that bank of ignition. Plugs, wires, or module. I would start with searching for a fouled plug on that ignition module... That's the least expensive and easiest fix... Keeping my fingers crossed.. That what was causing my issue. Do you run avgas? Could be a lead fouled plug. Link to comment Share on other sites More sharing options...
S3flyer Posted January 24, 2016 Author Report Share Posted January 24, 2016 I probably have 15 hrs of 100LL in the last 50 hrs including the last ~6 hrs. Link to comment Share on other sites More sharing options...
Jacques Posted January 24, 2016 Report Share Posted January 24, 2016 do you have EGT gauges for the 4 cylinders ? Link to comment Share on other sites More sharing options...
Roger Lee Posted January 24, 2016 Report Share Posted January 24, 2016 It may be nothing more than a spark plug cap off. It sounds electrical, but not 100%. I would start with my plugs. Check the caps. Check each plug and its gap. Check for thermal paste on a plug tip. If this turns up nothing then trim the plug wires 1/4" back at the plug cap end. Link to comment Share on other sites More sharing options...
S3flyer Posted January 24, 2016 Author Report Share Posted January 24, 2016 You win the prize, Roger, sort of. Turns out the spark plug wire on the bottom left plug (2B) was completely off and just hanging there against the exhaust. The 'Suppressed Spark Plug Connector' (Part 39 from https://www.cps-parts.com/catalog/rtxpages/912914dblignition2.php)had melted as well and left a pretty good mess to clean up. Anyone know the NGK part number so I can pick up at a local auto parts store or do I need to order from CPS? Also, presumably this is all I need? Link to comment Share on other sites More sharing options...
Roger Lee Posted January 24, 2016 Report Share Posted January 24, 2016 The plug caps from an outside source is a bunch cheaper. NGK VD05FMH You can find them online for about $7. p.s. So what's my prize??? Link to comment Share on other sites More sharing options...
Anticept Posted January 25, 2016 Report Share Posted January 25, 2016 Just a little FYI for anyone who reads this later and had boots that come off easy: often the pull off force problem is not the boot, but the plug itself. It can get wiped on one side even if you remove it just once. Save yourself a little trouble and look at the plug. If it looks a little flat on one side, take the plug, rotate it, and try again. If it pulls off easy still, replace the boot and screw the plug back in. If it's a lot harder to remove, replace the plug. Link to comment Share on other sites More sharing options...
cdarza Posted March 7, 2016 Report Share Posted March 7, 2016 Sharing info: 80HP 912UL. I had a Magneto problem where Left Mag had the 50-100rpm drop; Right Mag - no drop. Thus, both mags off and the engine kept on running. (choked it to stop) Long story of tracing where the problem might be and many days of checking the contacts, the switch, etc etc etc. Anyways cut to the root of the problem - one of the wires going into the module (i am not too familiar with which wire this is) had broken inside the sleeve. The wire looked totally fine from outside - but it looked a little stretched giving the idea it had broken inside - which it had. Luckily there as enough wire left to solder and reconnect- and all ok. Link to comment Share on other sites More sharing options...
Anticept Posted March 7, 2016 Report Share Posted March 7, 2016 That would be your ground wire. That's why you couldn't shut down. Aircraft ignition design is such that establishing a ground connection disables the system. That way, if there's a wire break or faulty ignition switch, it doesn't stop the engine in flight! Link to comment Share on other sites More sharing options...
cdarza Posted March 7, 2016 Report Share Posted March 7, 2016 Thats the one - Ground wire - Thanks Mr Hassell Link to comment Share on other sites More sharing options...
Runtoeat Posted March 7, 2016 Report Share Posted March 7, 2016 That's why you never touch a prop when you are around a plane with magnetos unless you're clear for a possible start. "Hot" mags caused by broken/poor grounds can leave ignition on with key off. Not so on our CT's with modules that require a fast spin to start. Link to comment Share on other sites More sharing options...
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