I had flown to Tampa for the weekend and was prepared to head back IFR flying through the towering cumulous clouds that are typical for this time of year in Florida. It was early evening and I had received my IFR clearance to DADES-V581-OCF-direct-CRG. The controller gave me a squawk code, frequencies told me to fly 060 on climb out to 1600 feet expect 8000 in 10 minutes. I ran through the runup checklist as I taxied to 36-Right as instructed. There was no traffic on the tarmac behind me or anywhere near the taxiway, so I felt safe in doing the runup on the roll.
Part of a runup is the run the engine at 1800 RPM, then turn off one magneto, then turn it back on, then the other magneto and turn it back on, then reduce the throttle to idle and verify that the engine would not die. I executed this procedure, or so I thought.
I had to wait for traffic to depart including a Boeing 737 which the controller referred to as an Airbus. I knew it was a 737 from the non-circular shape of the turbine intakes, but I didn't think it would be good to correct a controller for this minor detail.
I was eventually cleared for takeoff and I taxied onto the runway and gave the engine full throttle. The plane seemed to accelerate normally but as I climbed, I noted that I was barely getting 500 fpm for the rate of climb. I attributed this to the very hot day and high density altitude due to the heat and humidity.
I eventually leveled off at 8000 feet but was concerned when my speed was barely 107 TAS. I normally get about 124 knots and the engine was maxed out at 2400 RPM. I thought that maybe I had fouled a plug with the long wait on the tarmac, so I leaned the engine considerably until it ran rough. That didn't work.
I kept a close eye on the gauges and nothing was abnormal. What could be causing the problem?
Finally, I decided to run through my mental cruise checklist. This involves looking at each piece of equipment from top to bottom and left to right verifying that everything is as it should be. I started with the top left of the panel - all normal. Then moved downward. All circuit breakers were fine. But wait! There it was! Somehow, the start switch had flipped to the right magneto only position. It could have been because I had my whole keychain attached to the key or maybe I just didn't switch it far enough when I did the run up. I turned the switch to the both position and the engine instantly gained 300 rpm! Problem solved.
1.6 hours of cross-country flying with about .5 in actual IFR conditions.