I'm guessing, so my math could be poker-retarded.

Even though he's bad, he'll call with AK, AQ, AJ, AT, A9, A8, A7, A6, A5, A4, A3, and A2. That's about a 2 in 25 chance.

Having the 2 remaining Jacks is about a 1 in 25 chance.

You gain in the 1 in 110ish chance that he has KK or QQ.

You also gain in the 1 in 333 chance that he has 77.

Loosely estimated:
12 in 1,000 you gain.
12 in 100 you lose.

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