914 Low Power on Takeoff Attempt

Craig,

I understand what you are saying, however:

In the “bad flight” your fuel pressure dropped to 3 psi as compared to ambient, which is irrrelevant. What’s  important is fuel pressure in relation to airbox pressure.  The airbox pressure was 28 hg at the time, which is likely about 1.5 hg (.7 psi) below ambient, so your fuel pressure at that point is 3.7 PSI above airbox pressure.  That’s precisely where it should be.  I dont see anywhere in the graph where the fuel pressure deviates from what it should be.  This would be more apparent if you had a differential pressure sender, but the information is there either way.  The fuel pressure regulator is doing exactly what it should.

Yes, I don't believe the issue is in the fuel path at all. I think it's in the air induction path.

I ran the engine to full power and captured the TCU data (though the problem did not recur...). You can see it here if you'd like:

https://www.dropbox.com/scl/fi/877v24hlf53jwkbzmr6la/LiveLogs_9576763_2023-12-06_11-24-26.zip?rlkey=nelfbnxqrcpqczfczx9e2ndzx&dl=0

The Garmin G3X captured data can be seen here: https://apps.savvyaviation.com/flights/shared/flight/7629752/f62242c7-3df5-4cf0-911d-e7a7fea7214e

Meanwhile, I'm doing my 200-hour carb inspection and cleaning this Sunday and I'm hoping that completely resolves the issue. I think that because, as I've commented previously, there's clearly been some fuel leakage on both carbs.

> It just occurred to me that you should be sure that your fuel screens are clear. 

It's unlikely it could be this. The fuel pumps pump massively more fuel than the engine needs (think 40-50gal/hr). So the extra fuel required to go from idle to max power is only about 20% of the overall standing load. It's unlikely that could cause an outright pressure collapse.

@Jeff B, you're exactly right. Savvy Aviation's scales threw me for a loop. If we look at the very first graph on the first post and convert 11" of boost (41-30") into psi, we get 5.4psi. At the time, we have 9.5psi of fuel pressure. 9.5-5.4 = 4.1psi, which is very much within the range of acceptable fuel pressure. Apologies for going down a rabbit hole when the data, properly interpreted, clearly shows nothing of the sort.

“ the help we get on these engines is frequently well-intended but mistaken “