I remember selling and installing an aftermarket choke stove that involved drilling and tapping a 1/2" NPT hole in a manifold just above the exhaust pipe flange for installation. It was a loop of stainless steel tubing that was exposed to exhaust gas and included a filtered air nipple that was installed in the air cleaner and another tube to supply hot air to the choke housing. It worked pretty well, but it required a fair amount of labor time to install it correctly.
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!