On 8/21/15 7:57 AM, Arnie Goetchius wrote:
J Burns wrote:

Does yours backfire when you shut it off?

I'm getting intrigued. The only shutoff solenoid I was familiar with, was on the
Kohler engine of a John Deere riding mower from the late 80s. If it was to
prevent backfiring, I wonder why earlier engines didn't backfire when shut off.

I have a Simplicity from the early 90s with a Kohler engine. The carburetor
looks identical to carburetors with shutoff solenoids, but this carburetor never
had one. It was 20 years old when I got it. For the first year, it would
backfire perhaps ten seconds after I shut it off. For some reason, it hasn't
backfired in a long time. Whatever caused it to backfire, it doesn't need a
solenoid to prevent it.

It had no manual shutoff. The level in the tank was a little above the
carburetor. At first, I thought the valves in the fuel pump would prevent
seepage when it sat. I found that sometimes fuel would seep through the pump
and the float valve and into the cylinder. I wasted no time installing a
shutoff. The lack of one seems like poor engineering.

I never had a backfire before or after installing the shutoff. I did notice that
after installing the shutoff, the engine starts right up within a second or two.
Before the valve, if I could get the starter to turn over the motor, it would
take 15 to 20 seconds before the engine would start. I attribute that to the gas
that leaked into the cylinder.

Me too. I added a shutoff because occasionally when it caught after
several turns, there would be a puff of smoke and it would act flooded.
One can't count on a float valve!

Mine takes extensive cranking. Yesterday I counted 20 compression
cycles (40 revolutions) before it caught after sitting a week. The bowl
must empty as it sits with the fuel shut off, but how?

It doesn't seem possible that it could be siphoned into the cylinder,
and I've seen no sign of flooding. I've found no gas deposits or wetness
on the bottom of the bowl, or odor after parking in the garage, to
indicate seepage past the washer at the bottom of the bowl.

Could it be evaporation? Because the bowl is closed, evaporation should
be slow, but the carburetor is boxed in above a metal floor that gets
hot because it's over the muffler. Intake air would cool the carburetor,
but it could get hot after shutdown.

When I shut down, I lift the seat and plastic body to shut off the fuel.
I leave it up for three reasons: to let the carburetor cool faster, so
maybe I'll smell the fumes of evaporating gas, and so I won't forget to
turn on the fuel before trying to start. I've never smelled gas fumes,
and the engine still requires a lot of cranking before it gets gas.

I guess the next step is to use a stopwatch to see how much cranking it
needs after being off for various amounts of time. That may show how
fast the gas is disappearing.