Motor Fire

Motor Fire

1983 80 HP Merc
Out on the water, I ran a 6 gal tank dry, then hooked up a fresh tank. Primed the bulb, apparently one or both carbs were flooding from floats/seats not sitting properly after running them dry. Motor would not start. Apparently loaded up motor with fuel. Motor backfired and caught on fire. Pulled front cover and band off motor and extinguished fire quickly, got home ! to see no major damage, melted wires, etc. Pulled carbs, ( they were rebuilt this season and floats are at the proper height adjustment that factory manual says to set them.) and re-set floats/seats. Motor fired right up.

I have read threads here about carb/float flooding issues but haven't read one about any problems with floats/seats not sitting properly after running carbs dry. In fact, there is ongoing debate here about running carbs dry in order to avoid leaking carbs when tilting up motors for trailering, and to avoid carbs gumming up during the off season.

My question: is it simply time for new floats? They are original, although they don't seem to be saturated. Do you think the new plastic floats would fix my problem. Has anyone here experienced this problem?

Thanks in advance and would love to hear about anyone else's experiences with this carb issue.

Re: Motor Fire

My 1970 1150 always drips when trailering. Never had a back fire problem, or any other fire for that matter during normal use.

The things that bothers me about running carbs dry is that the engine is running very lean the final moments, which shouldn't be a problem, but in a multi-carb setup like mine the top carbs might empty first, because there's still fuel in the top carb's fuel line, that could keep the 2nd and 3rd carb going. Which might mean that the top 2 cylinders might run dry for a coupla minutes. Which would in turn mean that they are unlubricated for a couple of minutes.
Also, my engine has never backfired. Could this be because of a lean condition during the run-dry or start-up procedure?

So I don't run my carbs dry, ever.

Re: Motor Fire

Do you pre-mix oil and gas. If it's a VRO, the first gas after running it out wouldn't have any oil in it, and you would lose compression.

2 cycles generally don't back fire if flooded, but when they are lean, or poor compression, ie fire in the crankcase.

If there isn't a fuel filter in the line, debris from the bottom of the tank could hang the needle valves open.

Long story short, DON'T DO THAT. (run out of fuel)

hope it helps
John

Re: Motor Fire

You might just have picked up some dirt from the bottom of the tank,and it stuck between the needle and the seat.


DHP