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thinkn9a

Well Known Member
Looking for recommendations on sequence and settings for hot start, with dual pmags and fuel injection.

With just a couple tries so far, i have failed to come up with the magic combination.

My starter and battery thank you.
 
What engine do you have, compression ratio, sparkplug & gap, what timing are you running, and what fimware version is on the P-mags? If your P-mags are installed properly, they should help with hot starts.

Finally, what starting technique are you using?

Check you PM's.
 
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My technique

Feet on brakes
Half throttle
Mixture full off
No priming
Fuel pump off

Start cranking and slowly add mixture once she starts to fire up.
Adjust throttle as needed

Worked every time.
 
Same here

my technique for a hot start is same as Ryan only I set the throttle to about position that gets me about 1200 rpm, works every time
 
This is how I do it FWIW.

Throttle open 1"
Mixture full rich
Fuel pump on until you hear a distinct change in pump noise
Leave fuel pump on
No prime
Start as normal
When engine catches then throttle to idle (1000rpm)
Works for me every time

This is shown at: https://m.youtube.com/watch?v=7n_zwFfsQjs

:cool:
 
As I remember from the Lycoming class, the issue is that the injectors bleed down into the intake manifold over time - like 20mins or so. So regardless of anything else, you have a rich puddle of fuel that you are trying to ingest. So what you don't want or need is more fuel. What you do need is enough air to whip up the puddles and give you something ignitable and of course a thumping good spark to blow though it. Pretty assured your pmags fit that bill.

Again from memory, its mixture off, no prime, crack the throttle, twist until it lights then mix full and throttle to desired. You don't have to slam them home to keep it running. There's usually enough fuel lying around to keep it lit for a good 2 or 3 secs of 1000rpm, which is plenty of time really.

This is what we do in the Citabria and it works as advertised.
 
maniago said:
As I remember from the Lycoming class, the issue is that the injectors bleed down into the intake manifold over time - like 20mins or so. So regardless of anything else, you have a rich puddle of fuel that you are trying to ingest.....
Click to expand...

Which is why the purge valve in AFP's injection system makes good sense. When the engine is shut down there is no fuel in the flow divider to the injectors to bleed down.

Hot start (for me) is run fuel pump about a minute to circulate relatively cool fuel through the system, set the throttle about a quarter inch, hit the starter and go purge valve knob in and the engine starts right off.

It works for me because it is so simple, I have trouble with systems without the purge valve. :(
 
David-aviator said:
Which is why the purge valve in AFP's injection system makes good sense. When the engine is shut down there is no fuel in the flow divider to the injectors to bleed down.

Hot start (for me) is run fuel pump about a minute to circulate relatively cool fuel through the system, set the throttle about a quarter inch, hit the starter and go purge valve knob in and the engine starts right off.

It works for me because it is so simple, I have trouble with systems without the purge valve. :(
Click to expand...

I assume that a purge valve means that it just bleeds off the fuel pressure in the divider and lines, right? I assume that the AFP system has a fuel return line then - which the factory Lyc does not.
 
Yes, The purge valve needs somewhere to dump the pressure to. Fuel tank is best so you can also circulate fuel back to the tank prior to engine start.

Bevan

maniago said:
I assume that a purge valve means that it just bleeds off the fuel pressure in the divider and lines, right? I assume that the AFP system has a fuel return line then - which the factory Lyc does not.
Click to expand...
 
maniago said:
I assume that a purge valve means that it just bleeds off the fuel pressure in the divider and lines, right? I assume that the AFP system has a fuel return line then - which the factory Lyc does not.
Click to expand...

It shuts fuel off before the flow divider. The engine sucks fuel out of the divider and dies quick when this happens. Shutting down engine with mixture is never clean because fuel bleeds by mixture in idle cut off. They all leak. The purge valve does not leak, no fuel gets by it to the flow divider.

Yes there is a return line to one tank from the valve when it is closed to divider.
 
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More background

IO-320-D1A
8.5 compression
NGK BR8ES set at .032
No purge valve

Tried starting with throttle off, mixture at cutoff,.. No prime

jumper installed on pmag

Latest version of software,... Got them new about 3 weeks ago
 
thinkn9a said:
IO-320-D1A
8.5 compression
NGK BR8ES set at .032
No purge valve

Tried starting with throttle off, mixture at cutoff,.. No prime

jumper installed on pmag

Latest version of software,... Got them new about 3 weeks ago
Click to expand...

That's all GOOD!

The purge valve helps but isn't necessary.
 
thinkn9a said:
Tried starting with throttle off, mixture at cutoff,.. No prime
Click to expand...

Well, at some point in the process you gotta supply fuel if you want a fire. Cutoff and no prime is too lean to fire.

All methods base on a simple concept. The engine will fire when supplied a mixture that is within a fairly narrow range. So, the goal is to sweep the mixture through that range during the start process, either by beginning in a lean condition and moving toward rich, or beginning in a rich condition and moving toward lean. Either way, when you hit the sweet spot, it will light.
 
My engine has 10:1, Precision Airmotive Fuel Injection and Dual PMags with jumper wires installed.

I hot start mine by:

Throttle open ~1/2 inch
Mixture Idle Cut Off
No priming, boost pump Off
Starter engage
Mixture slowly forward ('slowly' is at a rate that would take you from ICO to rich in about 5 seconds) until it starts, which is usually about mid range.
Throttle as required to set idle RPM
Mixture lean
Boost pump as required to keep it from stumbling if the fuel pressure fluctuates.

Cheers

Nige
 
nigelspeedy said:
Throttle open ~1/2 inch
Mixture Idle Cut Off
No priming, boost pump Off
Starter engage
Mixture slowly forward ('slowly' is at a rate that would take you from ICO to rich in about 5 seconds) until it starts, which is usually about mid range.
Click to expand...

Yep, just like that!
 
maniago said:
I assume that a purge valve means that it just bleeds off the fuel pressure in the divider and lines, right? I assume that the AFP system has a fuel return line then - which the factory Lyc does not.
Click to expand...

Yes and no. Some people plumb the purge line to a tank and others run it back to just before or after the fuel valve.

The line is not used while the engine is running, like some FI systems.
 
IO-360, Bendix injection, 2 Pmags. (Prior: Mags and ElectroAir)

Prime
Throttle full open
Mixture full closed
Start.
As soon as it starts:
Throttle back to hi idle quickly
Mixture about 3/4 open (This is different on all planes)
If you have trouble keeping the idle, run the boost pump after it starts.
 
FasGlas said:
Prime
Throttle full open
Mixture full closed
Start.
As soon as it starts:
Throttle back to hi idle quickly
Mixture about 3/4 open (This is different on all planes)
Click to expand...

Above, Nigel does a mixture sweep from lean toward rich.

Randy (here) does a sweep from rich toward lean.

Either works. I do the Nigel, and if I miss the start, I flood it and do the Randy ;)
 
nigelspeedy said:
My engine has 10:1, Precision Airmotive Fuel Injection and Dual PMags with jumper wires installed.

I hot start mine by:

Throttle open ~1/2 inch
Mixture Idle Cut Off
No priming, boost pump Off
Starter engage
Mixture slowly forward ('slowly' is at a rate that would take you from ICO to rich in about 5 seconds) until it starts, which is usually about mid range.
Throttle as required to set idle RPM
Mixture lean
Boost pump as required to keep it from stumbling if the fuel pressure fluctuates.

Cheers

Nige
Click to expand...

I do this process only slightly different. I start with the Throttle fully open (all the way in) and Mixture at idle cut off. As I crank, I slowly pull the throttle and at some point in between the air to mixture ration is just right that it will fire. Then I slowly add the mixture to get it going. Granted, most of the time the engine will fire up when I am about ? open throttle, but with this method I believe you find faster where the sweet spot is for the air/mixture ratio.
 
I'm going with the "Nigel approach"

Thanks to all for comments and recommendations.

Tried a couple times with the Nigel approach, when hot, and it quickly fired and ran,.. No fuss, no muss

Ok,... I'll admit it,...second time i started with the mixture in just a bit,... Fed in just a bit more and off and running

Thanks again,.... Saved me from a science experiment
 
FasGlas said:
IO-360, Bendix injection, 2 Pmags. (Prior: Mags and ElectroAir)

Prime
Throttle full open
Mixture full closed
Start.
As soon as it starts:
Throttle back to hi idle quickly
Mixture about 3/4 open (This is different on all planes)
If you have trouble keeping the idle, run the boost pump after it starts.
Click to expand...

Wondering why the prime? In my experience, every hot start is a "flooded" engine anyway... Why make it worse? Aside from that, I'm with you - works every time.

I'd encourage you to try it without the prime and see what happens.
 
Toobuilder said:
Wondering why the prime? In my experience, every hot start is a "flooded" engine anyway... Why make it worse? Aside from that, I'm with you - works every time.

I'd encourage you to try it without the prime and see what happens.
Click to expand...

The prime makes sure you have some fuel in the cylinders. The purpose of the valve in the flow divider is to cut the fuel OFF when you cut the mixture. Without this spring loaded valve the fuel would drip into the cylinders. Some of you may have experienced this, your engine stumbles when you try to kill it with the mixture cut off. Adding some fuel and "Sweeping" the mixture, as Dan and few other have accurately suggested, insures your engine will "find" the proper mixture under most all conditions to get started. As it starts the engine will go from rich to lean (with the mixture closed and throttle open), this is when you add the fuel back into the engine by opening up the mixture. It's not perfect but it does work for hot starts, and adding the boost pump, after starting, for very hot starts.
 
I understand the theory, but in practice, there is plenty of fuel that percolates into the cylinders following shutdown. Thats the "gurgling" you hear as you walk away from the airplane. And it has been my experience that this after shutdown fuel flow is more than sufficient to "prime" each cylinder - even after several hours of inactivity. I'm not saying your method is wrong - because you obviously have good luck with it, but I will tell you that I NEVER prime a hot Lycoming and my "first try" success rate is essentially 100%, so mine works too.

All I'm suggesting is that you try it without the prime and see how it works. I'm highly confident it will save you an unneeded step.
 
Toobuilder said:
I understand the theory, but in practice, there is plenty of fuel that percolates into the cylinders following shutdown. Thats the "gurgling" you hear as you walk away from the airplane. And it has been my experience that this after shutdown fuel flow is more than sufficient to "prime" each cylinder - even after several hours of inactivity. I'm not saying your method is wrong - because you obviously have good luck with it, but I will tell you that I NEVER prime a hot Lycoming and my "first try" success rate is essentially 100%, so mine works too.

All I'm suggesting is that you try it without the prime and see how it works. I'm highly confident it will save you an unneeded step.
Click to expand...

My engine won't start unless I give it some prime. I don't give it very much but I do put some fuel into the cylinders for a hot start. Perhaps I have tighter tolerances on my mixture barrel and cut off valve then you do, so much less fuel seeps after shut down. One size does not fit all and you're mileage may vary. These are only suggested guidelines.
 
OK, fair enough.

I only suggested it because the last three airplanes I've had all behaved exactly the same WRT hot starts: 180HP, 200 HP and 260HP (and my 260 is a factory new engine). I also teach this technique to those "new" to FI Lycs, and their engines behave the same way. I have yet to run across one that didn't "prime itself" after shutdown, but clearly that does not mean they are not out there.
 
David-aviator said:
Hot start (for me) is run fuel pump about a minute to circulate relatively cool fuel through the system, set the throttle about a quarter inch, hit the starter and go purge valve knob in and the engine starts right off.

It works for me because it is so simple, I have trouble with systems without the purge valve. :(
Click to expand...

Where is the mixture set during this process?

Thanks,
 
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