white goop soup in carb bowls

That looks like water to me.

What did you find in the Sumps?

Is he running Avgas or Mogas?

Mogas with Ethanol (E-10) will eliminate the water problem as long as you run at least a half a tank through it each month.

If the plane does not see 10 hours of flight time a year, there is not a whole lot that will help.

- - -

If you want to verify that it is water...

Pour the sludge into a clean glass pint jar.

Fill the jar about 3/4 full of fresh E-10 Mogas. 

Shake the jar for about 10 seconds.

If the sludge goes back into solution and disappears, it was water.

The gas in the jar is now perfectly fine for use in any engine.

- - -

The worst thing to do to an engine is to run it without any Oil.

The second worst thing to do is to not run it at all.

Bill, et al --

% That looks like water to me.

OK!  I thought maybe an emulsion, but glad to hear H2O is likelt (except that that's bad for bowls, of course).

% What did you find in the Sumps?

One tank was clean, but one tank was *very* watery.  And he has a L/R selector, too, so he'd likely get total H2O when on that tank.

% Is he running Avgas or Mogas?

Oops!  Sorry.  AvGas only, AFAIK, and certainly at the moment.

...

% The worst thing to do to an engine is to run it without any Oil.

% The second worst thing to do is to not run it at all.

Agreed.  And boo hoo for this plane :-(

Thanks again!

I wonder if at some point, someone poured an aftermarket fuel additive into the fuel tanks and that’s what caused the sludge. What’s the fuel filter look like? Have all the fuel lines been replaced within the preceding five years?

 GIF,

I would drain all the water out of the system that you can find,  then top it off with E-10 Mogas to absorb the water you cant see.

An hour in the pattern should dissolve any remaining water into the alcohol.  It won't hurt anything.

When it is not being used, keep the tanks nearly full to keep the vapor head to a minimum.

If he will cover the fuel, offer to fly his plane for him once a month if he can't fly it himself. (Free Flight Time!!!)

Water usually enters the tanks as liquid water.  Not magic vapors.

Is there any chance this plane was left outside when it was raining or was hosed down for a cleaning and the Fuel Cap on the "Wet" tank is not sealing properly?