Manifold pressure gauge problem

[Dave Russell]

The manifold pressure gauge in my Super D is a pain. More acurately,
it's the line that connects it to the engine. Ten minutes of
aerobatics, and I can't get any kind of reliable reading; it just
sticks wherever.

It's easy to fix. A shot of air into the line (back toward the
engine, of course) and it's good to go, but this is becoming a real
bother. Can anyone tell me if there's a true fix for this, or am I
just doomed to blowing the line clean after every flight that I take
her inverted (i.e., as often as possible. :-)

Thanks,

-Dave Russell
8KCAB

[Dave Swartz]

I had a problem with the forward manifold pressure gauge in my Pitts
that was finally resolved by making the hardline that attaches to the
gauge longer so that it could be looped several inches higher than the
gauge before being routed back to the gauge. My problem was due to
fuel in the line leaving deposits on the inlet to the gauge that would
then restrict the pressure on the gauge and make it read low. Your
problem sounds somewhat different, but if you find you are clearing
the problem by blowing fuel out of the line, rerouting the line so
that the fuel (if that is the problem) drains back to the cylinder
might help.

Dave Swartz
Fort Lauderdale, Florida
http://www.FlightFantastic.US

[B]

G'day Dave,
sounds like it's getting a drop of fuel or oil into the line. Your fix is
easy on the ground but won't help much when you need it.

Far be it for me to offer ideas on unauthorised mods, but a valve and a T
piece in the line to allow fresh (filtered cabin?) air to enter the line
while the engine is running and pulling vacuum (or boost if turbo?) should
let you flush the line at your leisure. Should only take a second or two. Or
a filter may be added to the beginning of the line. Something like a cheap
plastic inline fuel filter may work nicely for the filter to a cabin air
source as it will not be trying to cope with much pressure difference wgere
one at the engine end may have to handle that and high temp and vibration.

Other option that may help is a larger diameter tube that would require a
lot more fuel or oil to block.

Hope this helps,
Peter



"Dave Russell" > wrote in message
om...
> The manifold pressure gauge in my Super D is a pain. More acurately,
> it's the line that connects it to the engine. Ten minutes of
> aerobatics, and I can't get any kind of reliable reading; it just
> sticks wherever.
>
> It's easy to fix. A shot of air into the line (back toward the
> engine, of course) and it's good to go, but this is becoming a real
> bother. Can anyone tell me if there's a true fix for this, or am I
> just doomed to blowing the line clean after every flight that I take
> her inverted (i.e., as often as possible. :-)
>
> Thanks,
>
> -Dave Russell
> 8KCAB

[Jerry Guy]

As Dave related, this is a bit of a problem with the Pitts S-2B, aat
least. I was given a piece of literature from the Aviat folks offering a
kit (for several hundred dollars) that was basically some plumbing
pieces that routed the manifold pressure line upwards behind the
cylinder. I just found a way to route it upwards without the kit, I
guess it allows the oil/fuel to drain back toward the head. Anyway, I
never had a problem again after the reroute.
As I recall there is also a vent orifice in the back of the gauge that
I opened one turn, then returned it to the original position on the
theory debris might have obstructed it. Good Luck.

Jerry

B wrote:
> G'day Dave,
> sounds like it's getting a drop of fuel or oil into the line. Your fix is
> easy on the ground but won't help much when you need it.
>
> Far be it for me to offer ideas on unauthorised mods, but a valve and a T
> piece in the line to allow fresh (filtered cabin?) air to enter the line
> while the engine is running and pulling vacuum (or boost if turbo?) should
> let you flush the line at your leisure. Should only take a second or two. Or
> a filter may be added to the beginning of the line. Something like a cheap
> plastic inline fuel filter may work nicely for the filter to a cabin air
> source as it will not be trying to cope with much pressure difference wgere
> one at the engine end may have to handle that and high temp and vibration.
>
> Other option that may help is a larger diameter tube that would require a
> lot more fuel or oil to block.
>
> Hope this helps,
> Peter
>
>
>
> "Dave Russell" > wrote in message
> om...
>
>>The manifold pressure gauge in my Super D is a pain. More acurately,
>>it's the line that connects it to the engine. Ten minutes of
>>aerobatics, and I can't get any kind of reliable reading; it just
>>sticks wherever.
>>
>>It's easy to fix. A shot of air into the line (back toward the
>>engine, of course) and it's good to go, but this is becoming a real
>>bother. Can anyone tell me if there's a true fix for this, or am I
>>just doomed to blowing the line clean after every flight that I take
>>her inverted (i.e., as often as possible. :-)
>>
>>Thanks,
>>
>>-Dave Russell
>>8KCAB
>
>
>