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OT Primer on a snowblower, how does it work?



 
 
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  #1  
Old February 1st 06, 09:33 PM posted to rec.crafts.metalworking
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Default OT Primer on a snowblower, how does it work?


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.

Thanks

Ads
  #2  
Old February 1st 06, 11:27 PM posted to rec.crafts.metalworking
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Default OT Primer on a snowblower, how does it work?

The float controls the level of gas in the float bowl, most carbs have a
small air inlet to keep it from air locking. On the primer bulb models,
this air inlet is hooked to the primer bulb. When you squeeze the bulb
the air pressure forces the gas down in the float bowl, and up into the
main needle, dumps raw gas into the carb throat. As soon as you remove
the pressure, the float needle opens a bit to replace the gas that was
pushed out. Radically simple.

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.

Thanks

  #3  
Old February 1st 06, 11:35 PM posted to rec.crafts.metalworking
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Posts: n/a
Default OT Primer on a snowblower, how does it work?

RoyJ wrote:
The float controls the level of gas in the float bowl, most carbs have a
small air inlet to keep it from air locking. On the primer bulb models,
this air inlet is hooked to the primer bulb. When you squeeze the bulb
the air pressure forces the gas down in the float bowl, and up into the
main needle, dumps raw gas into the carb throat. As soon as you remove
the pressure, the float needle opens a bit to replace the gas that was
pushed out. Radically simple.


And on some of them the bowl vent is a little hole in the center of the
bulb which gets "valved off" by your thumb covering it when you give the
primer bulb a push. Another very simple solution.

Jeff



OP snipped

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."
  #4  
Old February 1st 06, 11:55 PM posted to rec.crafts.metalworking
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Default OT Primer on a snowblower, how does it work?

Good stuff guys!!!

Thanks

Jeff Wisnia wrote:

RoyJ wrote:
The float controls the level of gas in the float bowl, most carbs have a
small air inlet to keep it from air locking. On the primer bulb models,
this air inlet is hooked to the primer bulb. When you squeeze the bulb
the air pressure forces the gas down in the float bowl, and up into the
main needle, dumps raw gas into the carb throat. As soon as you remove
the pressure, the float needle opens a bit to replace the gas that was
pushed out. Radically simple.


And on some of them the bowl vent is a little hole in the center of the
bulb which gets "valved off" by your thumb covering it when you give the
primer bulb a push. Another very simple solution.

Jeff

OP snipped

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."


  #5  
Old February 2nd 06, 12:04 AM posted to rec.crafts.metalworking
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Default OT Primer on a snowblower, how does it work?

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
  #6  
Old February 2nd 06, 02:46 AM posted to rec.crafts.metalworking
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Posts: n/a
Default OT Primer on a snowblower, how does it work?



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.)

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.

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!!

  #7  
Old February 5th 06, 05:04 AM posted to rec.crafts.metalworking
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Default OT Primer on a snowblower, how does it work?

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.

Jon
  #8  
Old February 5th 06, 02:55 PM posted to rec.crafts.metalworking
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Posts: n/a
Default OT Primer on a snowblower, how does it work?

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
  #9  
Old February 5th 06, 03:01 PM posted to rec.crafts.metalworking
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Posts: n/a
Default OT Primer on a snowblower, how does it work?

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
  #10  
Old February 6th 06, 05:22 AM posted to rec.crafts.metalworking
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Posts: n/a
Default OT Primer on a snowblower, how does it work?

hmm.
on all the 4 stroke snowblowers i've worked on, the primer bulb goes to
the vent of the carb. when you pump the primer, it pumps air into the
area above the float, providing pressure. This pressrue pushes fuel up
the main jet and idel jets into the throat of the carb.

when you tear the primer on the ones i have looked at, it still runs
fine.

an interesting gizmo is the boondocker nitrous system for snowmobiles.
it squirts nitrous into the air box before teh carbs, then bleeds a
very very small pressure off the nitrous pressure to mildly pressurize
teh float bowls for the extra fuel the engine rquires with nitrous.
truly ingenous.

 




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