Hi, My cessna 150 ran rough for about 15 seconds during the last 3 times I flew it. What would happen is at wide open throttle randomly the engine would vibrate, sound a little off, loose maybe 10-15% power. Then after about 10-15 seconds it would smooth out, power would restore and run like normal.This happened once during each flight of about an hour. Also, at initial startup the motor would sometimes sound a little off like its skipping a beat. But after warming up maybe 3 minutes would sound just fine. My mechanic did oil analysis and they found slightly high aluminum at the last oil change, and suggested to watch for morning sickness or sticky valves. After the motor ran rough for a moment again yesterday, we decided to pull the plugs tested compression and dumped the carb bowl. My plugs were not bad, compression was all above 78/80. He seemed to rule out the valves, or dirty plugs. There was not a bunch of crap in the carb bowl. He seemed to think the motor could of sucked some water thru the system, or could be a bit of carb ice, or the mags could need work. So he showed me a trick to tip the plane on its tail and shake it, then sump the tanks. I was amazed one wing I pulled out maybe a 1/4 of the strainer full of water about 10-12 times. Each time I would let it settle shake the plane on its tail, then sump it. This was after I had just flown it this morning after sumping it and experienced the bit of roughness. So there was definiteley water in the tanks, since I pulled that much out after. after doing some research about sumping these tanks I found http://www.sumpthis.com/cessna150andcessna152tanktest/cessna150tanktestimages1024x768.htm . These tests show the sumps are incredibly bad at pulling water from its lowest point. The author alleges that there could be many unsolved accidents with motor quitting that are caused by this design flaw. It makes me think my tank could still have substantial water in it. What practice are you guys using to sump your 150 tanks? My mechanic suggested sumping it aggressively, do it initially during preflight, run up the motor for 3 minutes.... kill the motor, do it again..... then do it before and after each time fueling and at the end of each flight. And tip the plane on the tail and shake it during each time. I have a belly drain too. I am thinking I should be sucking more than just one strainer thru to really test it. The only other thing the guy thought could be causing the occasional roughness was my mags, which are 10 years old since new, havnt been redone and have about 325 hrs on them. He suggests redoing them. Has anyone else dealt with water contamination in fuel in C-150 and what are your ways of insuring no contaminants ?