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wnorth(at)sdccd.edu
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 Posted: Thu Jun 15, 2006 10:13 am Post subject: Carb fuel/air distribution |
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Charlie,
While I do agree that the sumps and cylinders have some inconsistances, the
real culprit for A/F imbalance is in the old Marvel/Schebler, in the
throttle throat design.
The fuel discharge nozzle comes in at an angle and unloads about an inch
away from the throttle plate. This plate is only a balanced splitter of the
fuel flow when it is vertical (Full Throttle) and even then it isn't fully
balanced due to the angle of the discharge nozzle. So pretty much at all
times either side of the throttle plate sees entirely different ratios of
fuel and air going by. This is also true at idle due to the side location of
the idle and transition nozzles.
As well, it's only about 2.5 inches from the discharge nozzle to the flow
divider in the sump, not nearly enough distance to mix the air and fuel for
even distribution.
If somebody came up with a reliable and effective mixing plate that bolted
between the carb and the engine they might make some good money... they
might even get some of mine.
That all said my old M-S works fine everytime... even upside down if I don't
stay there too long.
W
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chaztuna(at)adelphia.net
Guest
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| Posted: Thu Jun 15, 2006 4:14 pm Post subject: Carb fuel/air distribution |
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Wheeler,
Thanks for the info on the MS carb. I haven't looked at one closely
in a few years. Basically, it reminds me of a scaled up Briggs and
Stratton lawn mower carburetor!  Do you know of any modifications
(experimental only) that can be done to improve this situation? From
what you describe, it doesn't sound like much can be done.
I agree about the short distance from the throttle plate to the
plenum. It sure isn't aerodynamic.
Charlie
| Quote: |
Charlie,
While I do agree that the sumps and cylinders have some inconsistances, the
real culprit for A/F imbalance is in the old Marvel/Schebler, in the
throttle throat design.
The fuel discharge nozzle comes in at an angle and unloads about an inch
away from the throttle plate. This plate is only a balanced splitter of the
fuel flow when it is vertical (Full Throttle) and even then it isn't fully
balanced due to the angle of the discharge nozzle. So pretty much at all
times either side of the throttle plate sees entirely different ratios of
fuel and air going by. This is also true at idle due to the side location of
the idle and transition nozzles.
As well, it's only about 2.5 inches from the discharge nozzle to the flow
divider in the sump, not nearly enough distance to mix the air and fuel for
even distribution.
If somebody came up with a reliable and effective mixing plate that bolted
between the carb and the engine they might make some good money... they
might even get some of mine.
That all said my old M-S works fine everytime... even upside down if I don't
stay there too long.
W
|
| | - The Matronics RV-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?RV-List |
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