kobelco sk330lc starting problems

I recently purchased a Kobelco sk330LC-6 Ser#YC07-Q1118. Upon my arrival the machine was already started & running. Tested it out all seemed fine other than a lower rpm's upon scooping a healthy bucket up. It arrives by us and the driver shows us how to start it(which the seller didnt disclose and the reason why they had it already running) 1st thing you have to do is reach down to the bottom of the seat and pull the manual shut off knob(located right behind your right heel when sitting in seat) all the way out and hold it. Then you have to turn the key to the start position. While the engine starts cranking you have to then slowly press the manual shut off inward. When the shut off is back in about 3/4 of the way the engine starts but chugging and blowing black smoke. Then you have to turn the key to the off position and then back on in a split second of time to prevent the engine from turning off. Once you hit the key off and then quickly back on the engine then purrs like a kitten and runs fine. Except stalls(almost as if it ran out of fuel) frequently, upon a high call for power. Recently we were operating the machine and it stalled(as it has done many many times) only this time we did the whole trick to get it started as usual and it back fired when we got to the turning of the key part. Tried the whole start procedure again and it started and operated for about one minute and then stalled again. Only this time it will not start back up. We tried a quick blast of either to see if it would fire up and it did. Only wouldnt stay running. So its definately not getting fuel . We just changed the spin on filter. and since it has been down we cleaned out the filter inside the water seprator. We found a huge amount of junk in there. Put it back together, primed it and still will not fire up on its own. We are beating our head over this one :Banghead Any suggestions? We do have the service / repair manual for it

kobelco sk330lc starting problems