Many Basenji puppies yodel. But when dispersed from the litter, they cease to vocalise.
However, all is not lost in your case. To make him continue as a songster, YOU must learn to yodel. There is no other way. As long as he hears it, he will continue to do it.
So stop everything, listen and imitate.
Mku yodels every morning and we have a long conversation which he obviously understands even if I don't know what I am telling him.
Some of mine have, over the years, come back to yodelling. Keepurr was 12 when he suddenly found his voice again. It wasn't a bad attempt and he looked so surprised each time he did it but again, we conversed to his entire satisfaction.
But tell me the name of your pup (registered name), parents and date of birth so I can add him to the Basenji on-line pedigree database ?