Ex-NBAer Jay Williams Turns Up The Heat On Andrew Schulz ... LET'S DOUBLE OUR 1-ON-1 BET

The smack talk between ex-NBA player Jay Williams and Andrew Schulz about their upcoming 1-on-1 game continues ... with Williams saying he's so confident he's willing to DOUBLE THE BET.

We got Williams and celebrity pastor Carl Lentz -- the guy who saved Justin Bieber's soul -- working out for the game in NYC when we asked him about Andrew saying he was too old and slow to win the game on Nov. 1st.

Williams then made a new proposal ... that the two men double their $500 bet to a cool $1k and give the money to one lucky Twitter fan of their choosing.

We also got video of Jay working out his game ... looks like he's still got it.

Okay, enough talking guys. Let's see this.