Thread: Engine Runs Rough in Rain

I went thru rain recently and the engine started to run rough. There were no "drop outs", just a roughness. I brought it back to the hangar and before shutting down, I noticed that the #2 key position seemed to run rougher than the #1 key position. I removed my cowlings and had my buddy use a garden sprayer to spray water into the ignition on each side and on top of the engine, while doing a static runup. I also had him spray directly into the engine air intake up near the windshield. The engine appeared to be sensitive to spray on the right side of the engine but marginally so. The #2 key position seemed to run somewhat rougher than #1 key position, but again not much different than without the water. I got around 200 rpm drop on #2 key position from "both" and about a 150 rpm drop on #1 key position from "both". The plane never did stall out during this water spraying. I was pretty impressed that direct water into the intake didn't stall out the engine.

I note that the plugs were changed about 25 hours ago and then they were regapped and re-installed about 20 hours ago. The carbs were balanced in the last 25 hours. The plug wires are original and are now over 3 years old. Does anyone have any experience with this sort of squawk? Is there a recommended time that the plug wires should be replaced? I note that there is a diagnostic procedure for the ignition system. Ohm resistance for plug wires/plug boots might be the next thing I look at?

I would'nt recomend re-gapping and re useing old/original plug's its asking for trouble ..

Rgs Mike

I would'nt recomend re-gapping and re useing old/original plug's its asking for trouble ..

I never reuse a crush gasket, including the one on the end of a sparkplug. At $3 each, it's false economy to ever put a used plug back into your plane.

Hi Runtoeat,

You should use plugs for 75 hrs. and toss them... If you use 100LL all the time and see at 50 hrs. you are having excessive lead build up on your plugs then 50 hr. intervals will be better. Just keep an eye on them and 75 hrs is a good change out time for unleaded or leaded fuel. Set the gap at .028 for moderate OAT. If you live in really cold country then narrow the gap to .024 and if you live in down right freeze your butt off country down to .020 is acceptable, but .024 will usually take care of it, but normal is .028.
What rpm are you doing the mag drop at? 200 rpm is too much. At 3400-3600 rpm the drop should be 60-90 rpm. No need to do mag checks at 4000 rpm. The higher the test rpm the higher the rpm drop. 115 rpm drop should be max, even 150 on the first mag is too much. Sounds like you are doing a high rpm mag drop check. I can't imagine both mags dropping that much other wise. Shouldn't be spraying your electronics with water and no, rain should not effect the engine run. The small amount of water that may enter the system while flying should go right through the engine. Do a mag drop at 3400-3600 rpm and then get back to us on the rpm drop.

Thanks for the replies guys. I totally agree that it is best not to regap and reinstall used plugs. Just sorting out squawks and making a "to do" list on my new plane. New plugs are the next item to do. Today, I tackled a high idle. It was at 2100 rpm and it was neccessary to constantly ride the brakes during taxi. Not good for brake wear. My friend is a LSRM and he set the idle down to 1700. Such a relief not to constantly be pulling the brake during taxi. I still note #2 ignition position is rough compared to #1 position and preliminary look-see with vacuum gages indicates that one side is running more vacuum than the other. Guess we'll probably go back in and rebalance carbs and then probably will have to tweak the idle again.

Roger, thanks for the good info on plugs. We'll do our best at straightening things out per recommended Rotax procedure for carb adjustment and will hopefully end up at or below the 90 rpm drop in 3400 to 3600 rpm range. I'll report back with results. I really appreciate everyone's comments and help. This forum is a great resource for all LSA fliers. I helped my friend deliver his CTLS to Leading Edge Airfoils in Wisconsin Monday to get some issues resolved. While there, I spoke with a ***** owner who was getting his plane repaired. He said he thinks this forum is the best for resolving concerns and for obtaining info.

Runtoeat,

Your right that the carbs have to be balanced to get correct data and not to cause excessive wear to your engine. Carbs will never be balanced at the 100 hr or annual and need to be set every time at those bench mark hours. I just did an LS inspection the last few days and the plane had 61 hrs. on it. The carbs were 3" of vacuum out of sync. That's alot since you want them to be equal. The crossover tube can only help so much to correct small imbalances.

Hey Dick: Quit flying in the rain!