Would like to understand logic behind hot start suggestions

[YankeeClipper]

I am not in need of suggestions for hot starting procedures--there are many posted indeed. But I want to understand those procedures and in turn better my understanding of the fuel injection system. My plane is an early model, and while the engines hadn't changed materially in this regard (to my knowledge) I know that some of the fuel plumbing may have. So if there are any substantive differences in the later models my diagram and logic here may not apply.

Looking at the attached, it looks like the throttle ("power") control is downstream of the mixture's on the fuel's journey to fulfillment. If that is so, why the suggestion (from some) to close the mixture fully, but open the throttle, when "priming" with the electric pump for a few seconds (the 15 or so often suggested)? Any setting after the mixture seems a moot point if you've closed the mixture.

[Learjetter]

Pretty good article on the system. There are others and YouTube videos on the topic as well.

https://www.avweb.com/ownership/cont...uel-injection/

Throttle = air
Mixture = fuel

You’re correct: priming with the electric pump does not result in fuel pressure or flow downstream of the throttle body if the mixture lever is in the cutoff position. It does ensure slightly less warm fuel is pressurizing the mechanical pump intake.

I’ll take a swing at it to start the discussion. I’m mostly a jet guy, but here’s my unlearned idea.

In many hot start situations, the problem (as I understand it, and I may be wrong!) is the liquid fuel in the divider and the nozzle lines becomes vapor-ed by ambient engine heat and isn’t effectively atomized under pressure at the nozzles…leading to an unburnable concoction in the intake. Shutting mixture off for a few spins of the prop while allowing full air into the cylinders “clears out” the cylinder so when fresh, less warm, liquid fuel is pushed under pressure to the divider when you push the mixture lever up, the result is a burnable concoction.

Essentially, by closing the mixture you’re ensuring no more warm/hot liquid fuel gets to the throttle body or the divider. The electric pump pressurizes the lines to the mechanical pump with cooler liquid fuel. And with the throttle full open you’re ensuring the max airflow into the cylinders to clear them out of whatever unburnable fog is in there. Then, while motor spinning, you open mixture and apply the choke by reducing throttle…and “bob’s your uncle” — she starts.

Usually. 60% of the time, it works every time.

Happy to be educated by folks that know more!
-LJ