High fuel flow alert

[jay507]

Interesting input, Tom. Will have a conversation tomorrow and then decide. 

Thank you.

[Skunkworks85]

On 9/17/2021 at 5:58 PM, Anticept said:

It's vapor getting purged. Vapor doesn't like to move unless a lot of fuel is flowing, and the moment it hits the carbs, they're suddenly going to vent at velocity. Your pressure will drop and your fuel flow will rise, then all will go back to normal.

The vapor sits in the fuel pump, I suspect, since that is where the heat will get to the fuel most easily.

This happens in my SW as well, under the following conditions:

1. Summer (hot) above 85°F

2. Longer taxi >5 mins (Heat soak of engine)

3. Running mogas

4. Not sure if it contributes, but my floats are on the heavy side of the spec, (Right under 7grams). I plan on new set soon, so maybe able to rule this out as a contributing factor. 

 

If i have 100LL i do not get the indication. 

 

 

[Anticept]

Avgas vapor pressure is 7psi (14.25 inhg). Mogas can be as high as 14psi, and as low as 8. It's for this reason that I think the issues are vapor related, because it's only brief that it happens. Old cars had problems with vapor lock until fuel pumps got installed in fuel tanks.

In addition, I think there is a gas bubble that gets trapped in the fuel pump even during normal operations. It isn't until the engine cools down, or that there is a call for a LOT of power that the bubble is cycled. I can even do a full power run at runup and still get the issue to crop up.

The old pumps (and I mean OLD pumps, pre-2010) never had these issues.

[Roger Lee]

This could easily not be vapor, but just a loose connection.