manifold pressure

[dan carley]

i have a rv-4 with 0320 and have been noticing the manifold pressure is lower than usually.
in cruise at 2400 rpm manifold pressure is 21" used to be 24"
and full throttle only around 24"

on the ground not running it always reads around 29" no matter what day.

could the gauge be bad?

thanks
dan carley

[lr172]

Doesn't seem likely that it is the gauge if it will accurately read 29" on the ground. Did you notice any reduction in performance with this change in behavior? Slower airspeed, reduced RPM, reduced fuel flow, etc.?

These readings indicate an increase in vacuum and should coincide with reduced power output. If you are seeing performance symptoms, I would check for blockage before the carb as my first step. Also be sure that throttle cable hasn't moved on you, prohibiting a WOT setting.

Larry

[SportAvServ]

Don't know how you have your MP plumbed but I had a 3 with slow MP response and sticking, the hose connected to the engine had swollen inside and restricted the air, gauge was fine.
Food for thought.
Rt

[C-FAH Q]

I had the same thing happen, I was using a aero quip hose. I took the hose off, squirted soap and water over the hose and plugged one end while pressurizing the other with the air hose. Hundreds of micro bubbles appeared everywhere on the hose. I replaced the hose and everything is fine again.

[Walt]

These hoses often accumuate oil in them, try cleaning them out.

[dan carley]

i did not notice any difference in performance same rpm's and same air speeds at rpm settings. just the gauge reads low

danny carley

[dan carley]

i think i found problem carb heat flap was locked in a little open position not sealing probably, think that would be it?


dan carley

[lr172]

Originally Posted by dan carley

i think i found problem carb heat flap was locked in a little open position not sealing probably, think that would be it?


dan carley

I don't think so. Seems several have had issues with blockage in the hose causing similar symptoms. Cleaning or replacing that hose would be my first troubleshooting step.

Larry

[dan carley]

i did clean out the line,was nothing in it. today's pressure outside was 29.92 while i had the line off the gauge 28,92. it's off 1 in. i don't think you can adjust the gauge.


dan carley

[BobTurner]

Originally Posted by dan carley

i did clean out the line,was nothing in it. today's pressure outside was 29.92 while i had the line off the gauge 28,92. it's off 1 in. i don't think you can adjust the gauge.


dan carley

They will only match if you are at sea level. If you are about 1000' above sea level it is correct.