Kobayashi has some Grade A beef with Joey Chestnut ... the former wiener-eating champ says JC is a huge cheater -- and is questioning if the guy is REALLY pounding 70-plus hot dogs!!!
We got Kobayashi out in NYC and he didn't hold back when we asked about Chestnut ... saying (through a translator) he thinks Joey's a food-chomping cheat.
"I've personally, definitely witnessed some cheating, yes," Kobayashi says. "One example, we were eating for a pizza P'Zone competition years ago and he was throwing the hardest part to eat -- the crust -- into the box the whole time."
In fact, Kobayashi thinks Joey is such a swindler, he's questioning Chestnut's most famous record -- 74 hot dogs in 10 minutes!!!
Kobayashi says Major League Eating is helping prop up Joey in order to drive interest in the sport ... and adds that he thinks the dogs Joey's been gobbling up are smaller than usual.
As for their relationship, Kobayashi says he and Joey just don't get along ... and he tells us he can't see himself EVER being friends with the guy.
By the way, if you're wondering what Kobayashi is up to these days ... he says he's about to enter a taco-eating contest in California -- and tells us he's got a dream job for the future!!!