55hp backfired, blew the cowl off, caught fire

[rookierobert]

I have an early 70's 55hp chrysler 2 stroke. I rebuilt the carb and fuel pump last year, it ran fine several times. First time out this year it fired right up, ran fine for 20 minutes then we slowed down to fish, i throttled back and boom. Big backfire, blew the lid off, blew out the carb bowl and caught fire. Luckily i had two extinguishers (used both) and no one was hurt...

Any ideas? I put it out pretty fast, doesn't look terribly damaged, is it salvagable? at min, it needs a new carb.

Any ideas why it went belistic on me?

 

[Frank Acampora]

Re: 55hp backfired, blew the cowl off, caught fire

I'll bet you had a gasoline leak. At high speeds, the air through the engine cowl would keep the vapors in check. But when you slowed down, enough vapors collected to be ignited by arcing points or other spark source.

A normal backfire just is not powerfull enough to blow off the cowl, and the fact that you did have a fire indicates the presence of gas.

Main concern would be the wiring and alternator or magneto coils. If the insulation is not melted, then everything else is repairable.

Makes you realize the power of gasoline and air. We all carry the equivalent of a good bit of dynamite on board. It pays to be extra careful in the presence of gasoline.

Although I always carry a functioning fire extinguisher, I have always had an "issue" with the requirement of carrying an extinguisher on a small boat. My reasoning is that fiberglass burns like the fires of hell. If my boat lights up, I'm going overboard, and if another is on fire, I'm not going near enough to use the extinguisher. I will pick up the people from the water, but their boat is toast.

However: Here is a case that proves big brother knows best, and I guess my issue must be put to rest.

 

[rookierobert]

Re: 55hp backfired, blew the cowl off, caught fire

I'll take a look at the hoses to see if one was loose. The bowl under the carb was off, i'd hate to think that screw came loose, i think it would have stalled first. In general, it looks ok, im going to sell it anyway, someone can either reapir the carb or use it for a parts motor. It needed a 75 hp anyway. On to craigslist I look.

Thanks for the feedback,. For me, i'll keep 3 extinguishers handy....