My car cuts off when I hit the brakes

I have a 91 Honda Accord SE. It has about 200k miles on it. To make a long story short we thought we had sold the car but ended up repossessing it after 3 months. The car was running fine when we sold it. Upon it’s return (and it was towed tour place) 1 of 2 things happens. When you turn the key it tries to start but can’t fully start or if it does start and you drive it around it is ok until you depress the brake pedal and then it kills the engine. Any ideas ?

Bad vacuum hose first guess.

Sounds to me that the brake booster has failed and it has a major vacuum leak when you hit the brakes.

I agree. Check all vacuum lines for a leak.

I WOULD NOT give a warranty, even to a family member (or, anyone), for any car as a private seller; especially, to a car this old. Car dealers aren’t likely to give a warranty past three months.
As waterboy says, this is a symptom of a vacuum WITHIN the brake booster, with the diaphragm ruptured. The repair is replacement of the brake booster. Check at a salvage yard (if you decide to repair this person’s car, at your expense).
I re-read your post. You REPOSSESSED the car. So, it’s YOUR car, again. Still, my stance doesn’t change on a “sold car which just won’t go away”.
Actually, it’s not your obligation, in any way, whatsoever. I just hate to see good people used.

I just hate to see good people used.

Yeah, but who else are you going to use? You can’t use bad people - they’re not worth a damn. (Sorry - just feeling goofy).

Yes, to the OP - the brake booster will almost certainly need attention.

However, it isn’t clear that this will solve the no start problem. If the no start was caused by some kind of a major vacuum leak (and I say major in terms of leading to a stall), and you did manage to get it started it wouldn’t drive around ok until you hit the brakes. It would run really poorly (probably surge & sputter & surge & sputter).

I’m not saying the no start can’t be related, but try to explain a bit better what happens when it doesn’t start. E.g. does it crank really well, but just won’t fire up? Does it crank and spit a little without starting? Do you end up smelling gas as you try to get it started? Everything about the no start might be helpful.