> Hey Guys
>
> OK kinda sortta have a better handle on 914 carburation. First off a turbo
> motor
> will run with very little fuel pressure, like gravity feed. It will only run
> however at ambient pressure or less. If you boost the motor will quit. The
> reason
> is if you boost the pressure in the venturi, it will blow through main and
> needle
> jets! You need to keep the pressure in the float bowl above that of the boost
to
> allow Berneulli to suck.
>
> They have a fuel pressure regulator to handle this task. If it fails and fuel
> pressure drops, you may be able to continue to make noise if you throttle back
to
> ambient pressure or less.
>
> The restrictor provides backpressure and return flow to fueltank. If
> restrictor
> clogs, fuel pressure regulator would still operate, but you may cause
> cavitation
> in the fuel pump/s. Even though the regulator is only allowing the correct
> pressure to get to the float bowl, if you had a fuel pressure guage at the
> pump,
> you would see a rise in fuel pressure. Vapor lock could occur with no excess
> flow. He said you should have a fuel pressure guage on all 914 installiations.
>
> Phil Lockwood said he dosen't think he has seen a full blockage. Partial usual
> makes motor run terrable. He said blockage is rare. On inital assembly not a
bad
> idea at all to blow out fuel lines, and prior to install of restrictor, to let
> fuel pumps run and let a gallon or so of fuel to run through system.
>
> There ya have it. A 914 is not fuel injected, you just need to turbocharge the
> float bowl a bit over full boost pressure so the venturi works.
>
> Ron Parigoris
If I understand the poorly translated Deutsch: The 914's carbs have
garden-variety float bowls, whose airspace is vented to the airbox. The
airbox will see as high as 38.4" MP, down to something less than
ambient. The regulator maintains fuel pressure relative to airbox
pressure, at 2.2-5.1 psi, 3.6 nominal, above airbox.
There must be no restrictor in the return line, and back pressure in the
return plumbing (which will include tank pressure head and fuel vent
pressure in flight) cannot exceed 1.5 psi to prevent overriding the
float valves and flooding. If the return line is blocked, regulation
totally ceases and the carbs will more assuredly flood -- around 20 psi
or so.
Regards,
Fred F.
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