Try mounting a small electric fan or a squirrel cage blower under the hood with a toggle switch in the cab, aimed at the carburetor. It's possible that the air coming from the fan is carrying enough radiator heat to heat, not cool the carburetor. This one is 12V, but there's probably something similar available in 6V if you're running an original electrical system.

www.ebay.com/itm/334921886428?

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!