I got 17#'s left in my bottle and when I hit the switch the engine misses and I can see black smoke coming out of the back, the guy at the refill shop said that I don't have enough....is he BS'ing me?

Alex

Once they are down to 2-3 pounds, they need refilled.

Your's needs filled.

A full bottle at your setting should be good for around 100 seconds of use, as long as you don't screw around turning it on and off (letting the pressure in the lines vent) and go around purging it.

My advice is to get a second bottle. That way, you'll always have a full one ready to go.

Make sure you have a pressure gauge and a bottle heater. Keep it around 900psi.

Good Luck!