On Wed, 01 Feb 2006 16:33:36 -0500, Roy wrote:


The primer button (bulb) on my 12 HP sears snow blower developed
a tear in it and the blower would only work while the fuel tank
was fairly full (3/4 or more) I replaced the primer assy and was
very much surprised to find out that all the button seemed to do
was to force air into a single line. To that point, I had
assumed that there would be an in line and an out line and the
button would force gas into the carb but of course the needle
valve in the carburetor bowl would prevent that, unless it were
open. So without wishing to tear all the covers off to find out
what goes where,, could someone provide me with some kind of a
word picture or link that describes how this primer assy, that
appears only to push air into a line, actually primes the carb.

There's basically 3 different type of primer bulbs that I've run
across so far.

One is the pump type where fuel goes in and then goes back out. Those
are used on 2 cycle equipment for the most part but instead of
actually pumping fuel into the carb they're actually pulling it
through the carb. The inlet is attached to the diaphragm side of the
carb behind the needle and the outlet goes back to tank.

The second is used on some of the cheaper Briggs engines with the
new style pulsa jet carbs. These are a in and out type of pump that
actually pumps fuel but they actually squirt into the throat of the
carb itself.

The last is the type that you run into. I've not actually gotten down
to the exact method they use but I think they use a siphon type setup
to pull some fuel from the float bowl into the carb. It's either that
or they pressurize the float bowl thus pushing some gas up the main
jet.

Wayne Cook
Shamrock, TX
http://members.dslextreme.com/users/waynecook/index.htm