Flying074

Thanks to everyone who replied to this thread. I went with the easiest solution first and alternated switching the fuel selector back and forth while pulling the strainer drain to see if I could shake the obstruction loose and get it to come out through the drain. I didn’t see anything obvious come out but afterwards I did a run up and then took the plane for a test flight. The blockage appears to have cleared and I had good performance for almost an hour on the right tank. Great info on the tank sealant and I’ll will look inside the tank next to see if there is any indication of flaking or peeling sealant to confirm whether this might happen again. Appreciate the forum ideas

I was flying from Olympia to Spokane WA in a 1967 M20F and was having an uneventful flight at 9000' when it came time to swap tanks. I rotated the selector to the right tank and within 2 minutes my fuel pressure dropped to almost zero and the engine started to sputter. I switched on the electric boost pump and the engine stabilized with good fuel pressure. Concerned, I switched back to the left tank which I had been flying on for the previous hour and the engine ran fine with good fuel pressure from the mechanical pump only. Seeing as I was over a large airport, I recreated the incident with a switch back to the right tank and the exact same thing happened. I swapped back to the good tank and landed. I started the engine in the morning on the right (bad) tank so I know the plane was getting fuel at low RPM and pressure from the right tank. I swapped to the left for the run-up and departure. At flying RPM, the fuel flowed perfectly from the left tank but did not flow from the right tank - only with the electric boost pump on. I initially thought this might be a clogged fuel tank vent so when I landed, I checked the right filler cap but did not get a noticeable indicator of a vacuum in the tank. I also tested the fuel again and didn't see anything concerning in the drain. The right tank was still full. My initial thoughts are: 1. partially clogged tank vent. I will test the vent tonight to see if I can blow air through it. Would a partial clog cause enough of a vacuum to inhibit the mechanical fuel pump from delivering enough fuel at high RPM but allow it to be overcome by the boost pump? 2. partial blockage of the fuel line to the selector valve. Could a small piece of debris or sealant from inside the wing tank have broken loose and gotten wedged into the line? It seems like a partial obstruction of the fuel delivery line could cause a drop in pressure. I keep the plane hangared and it flew great last weekend on both tanks. So, whatever cause this happened over the week or during my fueling this morning. Any thoughts what I should check before I pull it into the shop would be greatly appreciated. Thanks very much for any insight or experience with similar issues

Thanks again to everyone who has posted something in this. We cleaned the plugs (they were not fouled, but better safe than sorry) and soaked the injectors in solvent. The mechanic did tighten some leads that vibrated loose. The most interesting was the ignition housing inside the cockpit. When we turn the key to start it actually torqued the ignition housing which may have compromised or grounded the wiring. It's possible that caused enough juice to flow to crank the starter, but we weren't getting full spark from the magnetos. Upon inspection, the magnetos are still strong. The plane started and flew home yesterday. We will try to replicate the problem over the course of the next few days and see if we can figure out why this only happens the day after a flight when left outside. Whenever we have had problems, it's after overnight storage. With the grounding issues resolved by cleaning and tightening the connections, I'm hoping we can solve this problem with technique, not technology. Will continue to keep everyone posted and thanks again to the Mooney community! We have certainly added to our list of starting procedures and will find the one that works best.

Thanks to everyone for your thoughts on this so quickly. We are going to have the spark plugs and injectors cleaned which should be a good first step. If there is still a problem we'll come back up and seek some additional guidance (and share what the A&P thinks). Our cold start procedure is what Yetti lays out above. It usually works well but has been a challenge recently. We have shower of sparks ignition and the mags have about 400/450 hours respectively (I don't have my logs to confirm but both getting close to 500). The collective wisdom is a lifesaver unless we're trying to get to bed and start going down a rabbit hole of Mooney talk. Appreciate everyone's help!

My wife and I have a 1967 M20F ( IO-360 A1A). It is in good condition, with only about 160 hours on the engine since overhaul. Whenever she flies to an overnight destination, the next day the plane is extremely difficult to start. Out of the hanger, it starts easily. We have troubleshot many of the common issues - boost pump, P-leads, fuel flow, battery charge, and there doesn't seem to be a problem. Does anyone have any idea what might cause this? Humidity? We keep the plane hangared in North Carolina with a dehumidifier running. Leaving it out overnight on the East Coast subjected to more humidity than normal. Could that be a contributing factor? She has used cold start, hot start, and flooded engine procedures. I know this is minimal information, but I am a deployed servicemember and unable to get my hands on the airplane myself for a more thorough analysis. She is an Air Force pilot with several thousand hours of turbine time, but less experienced troubleshooting 50-year-old reciprocating engines. Appreciate any help or advice. We're both big fans of the forum.

Yetti, Thanks for the link! I was looking at a replacement Tach card but that will involve quite a bit more work than adding the limits with a sticker. The panel is already placarded with the limits but this is good stuff.

Thanks Andy, and everyone who jumped in. I'll call around and see what I can do about finding an A&P comfortable with installing and signing off on the work. Maybe someone more familiar with working on Mooney's will have less of an issue.

Thanks. I've spent a lot of time reading the forum but my wife and I just bought our M20F this summer and are looking forward to becoming participants. The Tach is the UMA 3 1/8" Electronic with TSO paperwork for it to be a primary. I picked it up from Aircraft Spruce and look forward to installing it. The wire from the sending unit is much easier to route than a new mechanical cable. I just need to make sure I am doing this legally. According to my FSDO, I should just get a replacement mechanical tach and cable, which is a step backwards in my opinion. Eventually I'd like to go with a full engine monitoring suite, but the money isn't there yet. Thanks

Sorry for jumping into this thread late. I recently had a problem with my original mechanical Tach in my 1967 M20F - instrument binding and the cable snapped. I would much rather install a more modern electric Tach than spend the money to find a replacement analog one. Does anyone who performed this replacement have a copy of the 337? I have the UMA tach and the installation is a cinch. However, the local FSDO told my A&P he doesn't support certifying an electric Tach as the primary for my plane. The A&P recommended I reach out for anyone who may have had this done already to show there is a preceident set. I appreciate any advice out there.