Unwise takeoff decision

[lpaaruule]

First of all, nothing bad happened, but I took of with my engine in a less than optimal state, and it continued to worsen as I flew.

I've been troubleshooting my autopilot servo that keeps disengaging almost instantly every time I try to use it. Thinking that electrical noise from the regulator might be the issue, I decided to unplug the voltage regulator, and just run off fully charged battery power for a short flight.

After starting the engine, I notice that my RPM was incorrect because I normally get it from the alternator, and must have my mag RPM set up incorrectly. During the preflight run-up it seemed like things we're quite right, as one of my CHTs was around 20 degrees higher than normal, and the engine just seemed different. I did the mag checks and one side seemed to have more of an RPM drop than usual judging by sound, but I didn't notice any EGT going cold.

On takeoff the plane climbed ok, but the CHT on one cylinder didn't come down as quickly as I expected it would, and the engine just didn't seem to have the punch that it normally does. I continued to adjust the RPM by sound.

My autopilot still disengaged almost instantly, so I dissapointedly returned to the pattern.

The engine continued to run more sluggish, and at one point it seemed to miss. Upon landing I did a mag check, and this time the engine ran really rough on one of the mags. Once parked, I took off the cowling to discover that one of the spark plug wires hanging loose from the distributor cap, and another only barely holding on. I must have bumped these when unplugging the regulator. I found that even when I plugged them back in, they didn't want to stay. Per the Jabiru manual, I expanded the contact, and they held much better. I'll do this on the rest of the contacts next time because I got tired of burning my arm on the engine.

So anyway, the error chain that we hear about in magazines was certainly on display yesterday. Like I said, nothing bad happened, but I was sure frustrated with myself. In my defense, the engine ran way better during the preflight mag check than after, but I should have aborted and checked things out. I don't think the spark plug became disconnected until I was in the air.

I'll be keeping a better eye on the spark plug wires in the future.

[9GT]

You should always "burp" the spark plug connectors when you attach them.. The boot tends to hold the air as you push them on and if they are not burped, the air pressure that built up as you pushed them on will try, and sometimes succeed, in pushing them off.

[sonex892.]

Hi Paul
One common and I believe recommended remedy to stop the leads coming loose on Jabirus, is to use a smear of RTV to glue the rubber caps to the bakelite distributor cap.

[lpaaruule]

Thanks for the suggestions. I’ll keep them in mind next time I get to the hanger.