Don't clearcoat the choke knob if it's wood which it looks like. Given it's age it'll most likely have a fair bit of oil worked into it from being handled and the clearcoat will never sit right. Best thing to do would be to give it a good going over with a quality beeswax, that'll bring out the grain in the wood and protect it from the weather. I love seeing stuff used in this way, my choke knob's a brass tap from an old water heater.
