The $400.00 dollar pumper is the new price, when the III model came out it wasn't that much more then the unpumped model, the huge jump in price was just over the last couple of years, OS was never cheap though. Your new pumper operates on a pressure pulse and draws the fuel from the tank to the pump to the regulator to the carb and off you go. Your tank must be vented or it acts like when you stick a finger over a straw and suck. Your engine shouldn't go rich or lean in the air, the fuel flow is regulated. The only disadvantage to them is when something quits working. There is a diaphragm in the regulator that will go out with age, they live a very long time though so not to worry. The pump itself can have problems and it is a part that can't be rebuilt, it needs a replacement, again, not to worry they last a very long time. My first 1.20 had a little choke attached to the carb, I still have a couple of them in my shop. It was just a wire rod attached to a flapper that you could twist and the little flapper went over the carb, one or two flips and the engine was choked, just like sticking your finger over the carb. Some people like to stick a finger over the muffler and give the engine a few flips to prime. I just hit mine with the starter and it takes a few roll overs and fires right up. I have to store some planes on there noses and the nasty castor will flow into the pump and gum it up once in a while. If you don't store them on the nose and you run your engine dry at the end of the day you will never have this problem. If you do you just need to clean it, not very hard to do, I use my heat gun and a pressure bulb full of fuel when needed.