Menu Sign In Contact FAQ
Welcome to our forums

Injection Engine Start-up science (or metaphysics !)

This is a note by MAPA about starting the M20E, which has of course the same engine IO360 as the F and the J model.

What I find interesting in this article is the idea that a successful hot start depends on the way the engine is shut down first.

Myself I’ve had my share of woes starting a hot Seneca a while back but as Boscomantico said, the best way for an individual airplane is to get someone who really has the trick figured out show you and then you do it the same way, every time. As long as we have to work with these antiquated engines not much else can be done.

LSZH, Switzerland

Perhaps it is sheer luck, but none of the fuel injected airplanes I regularly fly (P210, M20J, 172S) gave me any starting problems yet, no matter if cold, warm or hot. Our Mooney behaves exactly like in the video above: If you prime a hot engine too much, it takes two or three more turns of the starter motor, that’s it. The only difference for engine temps I make in my procedure is the duration of priming, and I always prime even a hot IO360 engine a tiny little bit. For the TSIO520 in the 210, priming according to engine temp, then mixture rich and slowly advancing the throttle while cranking works well.

OTOH in the last two summers, I have flown two different DA40s in the US, and both of them were often hard to start in various conditions. Same IO360 like in the 172, totally different behavior.

Friedrichshafen EDNY

Peter wrote:

Interesting… On a hot start I have always advanced the mixture fast (as soon as the engine starts up).

Then I have to reach for the throttle really fast to catch it and pull it back down, to stop the revs going too high.

I went through the embarrassment of failing to restart my Lyc IO360 (A3B6D) after taxying to refuel…I ran the battery down about four times …taking it out and recharging each time….cost me about two hours…and all the while my family were required to get back in for each attempt…and a repeated IFR delay message…,utter humiliation! I got it started eventually…after having it catch and then splutter while I frantically moved the mixture and throttle in random fashion to try and keep it turning…

I then installed a skytec starter (only to discover that for the 24v version it actually doesn’t spin faster than the Prestolite it replaced!)….and I replaced the Gill battery for a Concorde….

In the end I realized I’d been doing it all wrong…I hadn’t really thought about or studied what is actually happening to the fuel in the injection system on shutdown….I now realize that on shutdown the fuel in the injection system ends up in the cylinder….causing the engine to be slightly flooded….so my erroneous logic of only priming a barely warm engine for a second or so was just making it more flooded….the way to start is no prime and no mixture…throttle cracked (in fact don’t touch the throttle after shutting down from normal idle)….then as you turn it over the mixture in the cylinders gradually goes from too rich to just right (stoichemetric) and she fires right up! Then gently feed in the mixture to keep it alive…too fast and you will kill it on the rich side…too slow and it will die on the lean side… The more flooded you think it is the more initial throttle is used to accelerate the change from too rich to just right… No more embarrassment!

EGPD / OMDW / YPJT, United Kingdom

Well, three hot engine starts today with the TB20, all succeeded on first attempt.
1. after a short taxi to fuel after first start.
2. 1.5 hours after shutdown after a flight
3. after refuelling after the return flight.

POH procedure : 1/4 Throttle course (was more of a 1/2 course), Pump, Mixture goes gently up and down in a full second, pump off, fire it up.
When engine catch, or after a few turns if the engine don’t catch : mixture about 3/4.

On the first one, engine was about to die after putting mixture open, but finally survived.
On the two other ones, it was a pure beautiful start :D

Thank you all for your tips ;)


Pump [on], Mixture goes gently up and down in a full second, pump off, fire it up.

BTW I think the above is equivalent to

Mixture full, pump on for 1 second, pump off, mixture stays on full, fire it up.

This is because with the mixture closed, no fuel is going to flow through the fuel servo regardless of how hard the pump is pushing.

Shoreham EGKA, United Kingdom

with the mixture closed, no fuel is going to flow through the fuel servo regardless of how hard the pump is pushing.

I agree with that, but…

mixture stays on full, fire it up

Surely not mixture full rich for a hot start?


Whoops yes sorry

Mixture is returned to closed for the starting.

But does it matter? After all the throttle is returned to Max as soon as the engine fires up. Has anyone tried leaving the mixture on Max?

During starting, the fuel servo is not seeing any significant airflow, and therefore will not be feeding in any significant fuel, therefore the mixture lever position should not matter because all the mixture lever does is to control the slope of the air-fuel relationship. With no air, there will be no fuel going in, regardless of the mixture lever.

This is one graph for mine – RSA5 – which came with an overhauled servo I have on the shelf

So with wide open throttle there will be a bit of fuel flow. The bottom end of 25 PPH translates to 4.2 USG/hr which is about 1.8x the IO540 idle (fully leaned) fuel flow. Not much. (I assume the above is with a wide open mixture).

Shoreham EGKA, United Kingdom

Another video on starting:

Shoreham EGKA, United Kingdom
38 Posts
Sign in to add your message

Back to Top