backfire on carb'd 2 stroke?

[fastkenny]

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

 

[K Hultgre]

Re: backfire on carb'd 2 stroke?

Are you sure its a backfire and not a "lean sneeze". I would guess the carbs are crudded up from the winter and now are running lean.

 

[fastkenny]

Re: backfire on carb'd 2 stroke?

It sure sounded like a backfire - single loud BANG, or actually like a POP like a firecracker (could that be a sneeze?), just as the engine started. then idled fine, no coughing etc.<br /><br />Before I remove and clean the 3 carbs, what else could I check? I suppose a bad fuel pump could cause a sneeze, anything else? plugs? timing? I'll check the fuel filter / racor / etc. too.<br /><br />thanks