On Sat, 04 Feb 2006 23:04:39 -0600, Jon Elson
wrote:
Roy wrote:
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.
The later series of Briggs&Stratton engines (I think they call these
the Quantum series) use manifold pressure to wiggle a diaphragm that
pumps fuel up to a bowl under the fuel jet. When the bowl is
full, it overflows back into the tank. I think the primer
just wiggles the diaphragm the same way, but I haven't had one
of these carbs apart yet. If the broken primer button is
leaking some of the pressure pulsation away, the pump action
may be reduced, leading to fuel starvation when the tank
is low.
Hmm. Either they've got one out that I've not seen or you've got
some of the carbs confused.
Briggs has used the fuel pump up to the little bowl in the carb for
more years than I can remember (good reason to since they started
making them before I was born). It's called a "pulsa-jet" carb and was
the standard for Briggs on lawn mowers till they started using more
float type carbs (the last 15-20 years or so). There is a hold over of
the pulsa-jet on the cheaper lawn mowers. It's got a plastic carb with
the fuel tank mounted below it (the easy way to identify this type of
carb) and a red rubber primer button on the side. This is one of the
few style carbs where the primer button actually squirts gas into the
throat of the carb (thus the bulb is wet with gas). If you take the
air breather off and push the bulb you'll see the little jet of gas
shooting down the carb. When (not if) the bulb goes bad it allows the
carb to suck air into the gas circuit thus the engine won't run.
BTW these carbs don't use the crank case pulsations but rather
pulsations from the intake of the engine. Crankcase power fuel pumps
tend to be separate on 4 stroke engines. They're built into small 2
stroke engine carbs on the other hand.
Wayne Cook
Shamrock, TX
http://members.dslextreme.com/users/waynecook/index.htm