On Wed, 01 Feb 2006 21:46:26 -0500, Roy wrote:
Sorry for the slow response. It's been rather crazy around here and
I didn't have time to respond the day that I saw this. Then I forgot
about it.
Wayne Cook wrote:
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
Thanks Wayne
There is something fishy going on with this set up because I have seen
fuel come out of the torn primer button and since becoming torn the blower
loses power and stalls out when the fuel level in the tank gets down to
about the level or physical height of the primer button. Now my logic
tells me that if the primer line fed into the top of the carb bowl, then
no fuel should ever get back up to the primer button unless the needle
valve was stuck open and the fuel in the bowl could fill the entire bowl
and then could find it's way up into the primer button and on out the tear
(or the tiny air hole in the button.)
Ok. Sounds like you've got a float type carb on there.
The above seems reasonable to me but it does not explain why the engine is
being starved of fuel when the the fuel level in the tank drops. I do not
recall having any such fuel starvation problem before the primer button
became torn. So I don't really know what's going on.
It does sound fishy. It almost sounds like you've got a setup with
the fuel tank lower than the carb. In that case there's going to be a
fuel pump somewhere. It may be screwed to the side of the carb (on the
input line) but that's rare for Briggs. More likely is that it's
screwed to the side of the engine somewhere. Trace the fuel line from
the tank to the carb. If there's a rectangular object some where in
line with three hoses going to it (one will go to the crank case) then
that's the fuel pump and is the most likely cause of the problem.
Just now waiting for the next snow fall to see if the new primer button
solves the stalling problem. I have a sneaking suspicion that I'll have to
clean up the needle valve and seat. (perhaps install a kit)
Thanks again!!
You're welcome.
Wayne Cook
Shamrock, TX
http://members.dslextreme.com/users/waynecook/index.htm