Aaron
Aaron
Try to keep the center of your header tank AT or slightly above the
needle-- This will ensure that you always have postive head pressure on
the needle and the tendency will be to run slightly rich; by mounting
the tank slightly higher than the needle you will have a gravity-feed
system instead of the dreaded venturi suck.
Kelly
In article <373FA833...@calpoly.edu>,
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Aaron
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Ergo_Bill
The fuel feed pressure that the carb "see's" is a combination of exhaust
tapping pressure + the head or weight of fuel which is governed by it's
relative height to the centreline of the carb main needle.
Having a small header tank ( 2oz) or so right on the centreline of
the carburettor will only be at the optimum height when the main (larger
tank is empty.
If the main tank is higher or lower than the centreline of the carb
needle (heli's are usually lower) then this creates a setup where the
mixture leans off as the main tank empties and richens up when the heli
is inverted.
Some engines are very sensitive to relative tank height and exhaust
pressure ,some are not.
Aside from the head of fuel and exhaust pressure issue,there is also
another factor which is the carbs own ability to draw fuel,this is
largely governed by the relative bore of the carburettor for the engine
displacement and the amount of engine compression.Large bore
carburettors are more sensitive to tank height and more prone to fuel
draw problems than small bore carbs are.
IMO header tanks are only useful as a means of always keeping a "still"
tankful
of fuel ,even when the main tank may be foaming (boiling) like hell,
when it's nearly empty.So it increases the reliable run time and avoids
lean runs by always picking up unbubbled fuel,hopefully.
Martin
Steven655 <stev...@aol.com> wrote in message
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