Restrictor valve for manifold pressure

[bradp]

On my first day of Mooney ownership - upon picking up the plane - the landing light was out and traced to a bad connection.  The totally unknown to me mechanic replaced the lead to the landing light and noticed there was a hole in the manifold pressure tubing and said he had fixed it.  Okay.  He also handed me something that he said was restricting the manifold pressure and that I didn't need it. 

Several years later after I have always noticed the MP to be too high by about an inch or so I did some investigating (I don't have a Turbo!). Thinking back to my first day...

1) The calibration port (you have a hole in your manifold tubing!) is now open again

2) The restrictor that was removed at the same time.  It's missing.

I'd like to replace the restrictor to see if it brings the gauge back in line before I trouble shoot anymore.  Upon searching the parts catalog I come up with two candidates for the restrictor, part numbers:

660155-001 (Eff SNs 24-0084, 24-0378 thru 1378)

660155-005 (Eff SNs 24-3377 thru 24-3404

660155-007 (Eff SNs 24-0084, 24-0378 thru TBA)

My plane is a 1977 J SN 24-0348.  Doesn't map to any of those part numbers...

Does anyone know what the correct part number is for this restrictor for a 77J and whether the Mooney part maps to a Milspec or other commercially available source?  I know that there were folks that had issues on installing JPI MP gauges (bouncing / erratic) who got a hold of a restrictor... Snubber.... Scupper...  Snuffer.   Etc.  Whatever you actually call it. 

Thanks for your help and take care,

Brad

[N201MKTurbo]

The restrictor should not change the reading, it will just smooth out any pulsations in the reading.

[INA201]

I'm interested in this discussion as well.  I bought N5201D in September(1978 m20j 24-0578) that had an inop mp gauge. My mechanic spotted the micro hole in the hard line coming from the intake so he replaced it. I mentioned that it needed the hole to balance oscillations in the gauge so we drilled it the appropriate size. It still doesn't act right. I hopefully am not corrupting bradp's thread but was wondering if there is a best practices method of hooking up the mp gauge to reliably correct this issue. Maybe the restrictor is what I'm missing as well.

[carusoam]

Working on using some words...

1) the tiny hole in the MP line is a calibrated leak.  It's purpose is to keep fuel from working it's way back towards the instrument.  The fuel that evaporates in there leaves a blue goo remnant that is bad for instruments.  So the calibrated leak is there for a reason. Blocking it, gives bad data.  Having the line crack open at the calibrated leak allows the MP to appear much higher than it really is. I have posted the diameter of the tiny hole previously.  It is smaller than any drill that you have bought in a set from HD.  Let me know if you can't find it.  It was for a '65C, if that makes a difference...

2) the snubber is a tiny hole that allows small amounts of air to access the gauge.  It essentially acts as a resistor to smooth out the fluctuations in pressure that are naturally in the line.  There are many fluctuations caused by intake valves opening and closing.

3) The dimensions of calibrated leaks and snubbers are important.  They will directly effect the gauge's reading. I found the MM may have these.  A discussion with somebody at Mooney Service may be helpful.

4) Bob went through a lot of effort when installing his JPI to get a proper snubber when the electronic version of a snubber was unable to do the job properly.

5) Snubbers are in the line. The wrong size may effect the oscillation, but not the average value.

6) Calibrated leaks are holes that go outside the line.  The wrong size will give an error in the reading.

I am only a PP, not an instrument technician...

Best regards,

-a-

 

[N201MKTurbo]

The hole should be 0.040"