Spray Bar alignment
04-24-2011, 10:11 PM
#26
RE: Spray Bar alignment
ORIGINAL: Kweasel
Our rotating barrel carbs lose fuel draw at part throttle, the venturi effect is lost as the barrel closes.
Our rotating barrel carbs lose fuel draw at part throttle, the venturi effect is lost as the barrel closes.
04-24-2011, 10:17 PM
#27
Senior Member
Thread Starter
RE: Spray Bar alignment
Kwesal, I have no intention in modifying the spray bar, just changing is orientation to the air flow. The regrind of the cam grove in the barrel is not something I would attempt at this point. This isn't an effort to get an engine running well, but rather to gather information on how the barrel carbs reacts to different orientation of the spray bars. Pure curiosity at this point.
Don
Don
04-25-2011, 02:40 PM
#28
My Feedback: (29)
RE: Spray Bar alignment
ORIGINAL: Mr Cox
On the contrary, an engine without the airbleed, or a metering slit in the barrel, will run too rich at low throttle settings.
ORIGINAL: Kweasel
Our rotating barrel carbs lose fuel draw at part throttle, the venturi effect is lost as the barrel closes.
Our rotating barrel carbs lose fuel draw at part throttle, the venturi effect is lost as the barrel closes.
04-25-2011, 05:11 PM
#29
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Join Date: Dec 2001
Location: Colonial Beach, VA
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RE: Spray Bar alignment
I know that the best way to rescue a flight when the engine leans at full throttle is to quickly cut the throttle and the engine will pick right back up, every time.
04-25-2011, 05:21 PM
#30
Senior Member
Thread Starter
RE: Spray Bar alignment
ORIGINAL: Kweasel
If the fuel draw remained constant the mixture would become increasingly richer as the airflow decreased. Fuel draw and airflow decreases as the barrel is closed.
ORIGINAL: Mr Cox
On the contrary, an engine without the airbleed, or a metering slit in the barrel, will run too rich at low throttle settings.
ORIGINAL: Kweasel
Our rotating barrel carbs lose fuel draw at part throttle, the venturi effect is lost as the barrel closes.
Our rotating barrel carbs lose fuel draw at part throttle, the venturi effect is lost as the barrel closes.
"Since the barrel restricts the air flow both before and after the main nozzle, the main nozzle is always acted upon by the same amount of vacuum, essentially a variable venturi."
and
"The advantage of the barrel valve design is the it provides for a very even air/fuel mixture thoughout all throttle settings."
These comments from Walbro seem to contradict your comment.
A fuel slot or air bleed fine tune the mixture. Part throttle draw is improved by opening the bottom of the barrel more than the top.
Don
04-26-2011, 02:37 PM
#31
My Feedback: (29)
RE: Spray Bar alignment
ORIGINAL: Hobbsy
I know that the best way to rescue a flight when the engine leans at full throttle is to quickly cut the throttle and the engine will pick right back up, every time.
I know that the best way to rescue a flight when the engine leans at full throttle is to quickly cut the throttle and the engine will pick right back up, every time.
04-26-2011, 04:57 PM
#33
My Feedback: (29)
RE: Spray Bar alignment
ORIGINAL: Campgems
My quote from the Walbro service manual
''Since the barrel restricts the air flow both before and after the main nozzle, the main nozzle is always acted upon by the same amount of vacuum, essentially a variable venturi.''
and
''The advantage of the barrel valve design is the it provides for a very even air/fuel mixture thoughout all throttle settings.''
These comments from Walbro seem to contradict your comment.
Measurements on a Saito, ST, and Walbro barrel carbs seem to also contradict this statement. The openings were symmetrical top to bottom.
Don
ORIGINAL: Kweasel
If the fuel draw remained constant the mixture would become increasingly richer as the airflow decreased. Fuel draw and airflow decreases as the barrel is closed.
ORIGINAL: Mr Cox
On the contrary, an engine without the airbleed, or a metering slit in the barrel, will run too rich at low throttle settings.
ORIGINAL: Kweasel
Our rotating barrel carbs lose fuel draw at part throttle, the venturi effect is lost as the barrel closes.
Our rotating barrel carbs lose fuel draw at part throttle, the venturi effect is lost as the barrel closes.
My quote from the Walbro service manual
''Since the barrel restricts the air flow both before and after the main nozzle, the main nozzle is always acted upon by the same amount of vacuum, essentially a variable venturi.''
and
''The advantage of the barrel valve design is the it provides for a very even air/fuel mixture thoughout all throttle settings.''
These comments from Walbro seem to contradict your comment.
A fuel slot or air bleed fine tune the mixture. Part throttle draw is improved by opening the bottom of the barrel more than the top.
Don
04-26-2011, 05:46 PM
#34
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Join Date: Dec 2002
Location: Lakewood,
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RE: Spray Bar alignment
One thing that hasn't bin mentioned is the positive pressure of the fuel going to the carb from the tank being pressurized from the muffler tap.
I'm sure this adds to the mix as well.
Jeff
I'm sure this adds to the mix as well.
Jeff
