The first two times starting my stbd motor ('88 Yamaha 150) after winter layup, there was a loud 'BANG' backfire. It sounded like it came from the exhaust, not the carb, but hard to tell since I was up at the helm. It was running on muffs, with good water pressure, and after the first start it idled well for several minutes. It sat for an hour or so, and backfired loud again on the second start.<br /><br />First time, took a while to start (2 or 3 tries, 5 sec each) and used choke, second time it started right up with no choke.<br /><br />I was ready to install the new fuel pumps, but remembered reading that a backfire can rupture the diaphram, so I thought I'd investigate the backfire first.<br /><br />Is this common when taking motors out of winter storage? Is there anything I should check before installing the pumps? Clymer manual has nothing on this.<br /><br />THANKS