Fuel mixture

I am a new ercoupe owner (N2409H) and live in Klamath Falls, OR, elev 4100 ft. Recently I have lost power on take off several times, especially with density altitude above 5,000 ft. My local A&P suggest that I need to lean the mixture immediately after start-up (we have a long taxi for take off since LMT is a military training base) and leave the mixture leaned on take-off and landings. I am concerned about engine head temps and I don't trust the cylinder temp gauge tp monitor this practice. Any suggestions will be appreciated.
UncleBilly