I've seen several secondary needles that just disappeared, followed by hammering noises from the engine. Pull the head- - - -there's what's left of the needle stuck in a piston! It usually happens on engines that spend a lot of time at or near full throttle, where the secondary air flap cycles a lot. That carb is sort of like half a Quadrajet, with all the bad features and none of the good ones. Keep an eye on the needle, and if it shows signs of getting wobbly in the air valve, use the carb for a fishing sinker!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!