I bought a lawn chief 12/39 used.The problem I am having is it starts very hard and I usually have to jump start it.When I do get it started.I can drive around all day without problems and it can also sit idle with the mower running but when both are engaged it stalls.It has a 12hp briggs engine in it.

Thanks,
Karl

First make sure all your connections are good, make sure the battery connections are not corroded and are tight... battery new? Replace it if its 2 years or so old... that's about they're lifespan.

So when you engage either one, at the same time it cuts out? Does it choke out or shut right off? Briggs I/C?