The week before last the neighbor brought home a snow blower that had been
at his mom's house for several years. It has a rather ubiquitous single
cylinder carbureted four cycle engine on it. On Friday he got it started but
it would only run if the choke was full on. It ran well enough that he could
clean the light snow from the driveway so he thought he was "home free".
The next day he tried to start it and nothing other that starting ether
sprayed in the carb would make it run. After watching him for a while I went
over to see if there was anything I could do.
Like any good doctor I wanted the patients family history. The machine had
sat unused unprepared for long term storage for two years. Last year he had
tried to get it going but couldn't so he left the new gas that he had put in
the tank just sit there and allowed the machine to sit idle for another
year. Which brings us to last week.
He had sprayed carb cleaner down the throat of the carb and had removed the
float bowl. While I was there we removed the idle and main jet adjustments
and used the straw of the carb cleaner to shoot cleaner thru the internals.
Based on what I saw the passage from the idle adjustment to throat of the
carb is clear ... or at least allows carb cleaner to flow easily ... and the
same from the idle adjustment back to the fuel bowl. The same appears to be
true for the main jet ... at least some flow to the throat and the other end
sits in the fuel bowl so that end works.
We then checked the float level and when hanging freely fuel flows quite
nicely from the tank, when the seam on the float it horizontal ... or
parallel with the bowl base the fuel stops and does not start again as the
float reaches the end of it travel. So we feel the fuel system up to the
float in the bowl is working correctly.
We put it all back together and tired it and zero, zilch, nothing. On a whim
I stuck my thumb over the throat of the carb and blocked off 95% of the
opening. When I did so it actually started and would run as long as my thumb
was there. This really surprised me because the opening to the throat of the
carb was so small I didn't think enough air would get in for any combustion
to take place.
The bad part is that when I remove my thumb the motor dies. Full choke does
not seem to block off enough to either get it started or to allow it to run.
The only way we can make it run is with a thumb in the throat of the carb
... or 95% of the throat blocked off.
Adjustment of both the idle and main jets do not seem to have any effect on
the percentage. We had them anywhere from 1/2 turn to 3 turns from "seated"
and no difference.
As mentioned, I was awestruck that it ran at all with such a small opening
to the outside air. We spent some time looking for a vacuum leak just to
make sure air wasn't coming in from somewhere else. But with only a carb, a
three inch long, two 90 degree bends, cast metal intake manifold and then
the flathead cylinder, there are only two gaskets to check, and both passed
the "spray ether on them" vacuum leak test.
At this point I am open to any and all suggestions as to what to do next.
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