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Airflow Performance Hot Start tips?

13brv3

Well Known Member
Greetings,

I continue to struggle with hot starts, even though the Airflow Performance system has a purge valve that's supposed to make this easier. Cold starts are great, never more than a couple revolutions before it's running, but hot starts are hit and miss, and recently more miss than hit.

When it won't start, there's no firing at all, which leaves me thinking it's either flooded, or has no fuel at all. If anything, I think I might not be giving it enough gas, likely compensating for all the horror stories you hear about hot starts on injected engines.

My question is how many seconds of priming action do you give when the engine is thoroughly hot, and has been shut down for 15 min or so? When cold, I give it a count of 5, but hot I try to use no more than 1 second. Unless I hear otherwise, the next attempt will be with about 3 seconds, or maybe 5 seconds like when it's cold. Is it possible that the purging is just so good at cooling the lines and eliminating vapor that I don't need to be so concerned about flooding?

Hopefully I won't have to start looking for a carburetor :)

Thanks,
Rusty
 
No Prime

On the IO-375 in my Sportsman with the AFP system (no purge valve) I never primed it hot. Hot procedure was:

Throttle cracked open
Mixture Idle Cutoff (ICO)
Key to Start
When engine fires slowly move the mixture control toward full rich

It always started very easily hot or cold.

It is very easy to get too much fuel in the system.
 
PURGE VALVE

Hey Rusty:

Remember you have the purge valve installed - or your post suggests this.

If I can recall what Don said about this: for a hot start, purge valve open/ICO position, and flush system with boost pump until cool fuel is in place.

I would add that you should be starting from the tank that has the return line to it so no fuel sprays on the ground from your vent system.

No fuel will go into the engine, or on the ground - when purging. This assumes that you have the system installed correctly.

Once you purge (Bonanza owners use 60sec of boost run time - you might get away with less) you can tickle the system with a bit of fresh fuel with the purge valve closed/set to run position - not too much tho - then try to start with the mixture rich, and the throttle set at about 1000RPM.

Another option is to swap out to an SDS system, which will lighten your wallet substantially. Starts like your car - quite amazing.

Seriously, the purge setup is very good, but it sounds like you are not using it as designed, again assuming that it is installed correctly. A quick call to Don will get you straightened out, no matter what is going on.

Good luck!
 
My question is how many seconds of priming action do you give when the engine is thoroughly hot, and has been shut down for 15 min or so?

None.

You are most likely idling at shutdown, which is a happy place for both the mixture and throttle. Just use the bypass valve to shut the engine down, not the mixture.

For restart, with the bypass still open, turn on the boost pump while you get buckled in, boot up the EFIS etc. Throttle and mixture still where you had them at shutdown.

Now start cranking and slowly close the bypass. Boost pump off after start.

This is what I used in my 10-----worked well for me.
 
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Do you have electronic ignition?
We have PMags and when we switched to automotive spark plugs, our hot start problems disappeared.

TIFWIW.
 
After shut down, the fuel in the lines between the injector and the spider boils. The expansion causes this fuel to be pushed into the intake area of the cylinder head, leaving a very rich mixture once you start cranking.

I have no purge valve, but my procedure is Throttle cracked as normal, mixture rich and boost pump for 1 second. This refills the injector lines with fuel and adds a bit more fuel to the intake area. Then mixture to ICO and crank. Once it begins to catch (usually 5 seconds or so), move to full rich on the mixture. It usually keeps running, but sometimes doesn't. Next start effort, if it didn't catch, is throttle cracked and mixture rich with no priming and it will start in a blade or two.

Larry
 
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Hey Rusty:

Another option is to swap out to an SDS system, which will lighten your wallet substantially. Starts like your car - quite amazing.

Trust me, I do plan to look into EFI :)

Thanks to all for the comments. The checklist that came with the plane had another procedure that left the purge valve in the run position during start, but then moved mixture from cutoff to rich. I had the official procedure with me yesterday as well, moving the purge from off to run while cranking. I tried that yesterday, but perhaps the damage was already done by then.

Next time out, I'll try to official procedure, without any prime, and see if that makes a difference. I'll just have to make a practice of letting the plane sit a few minutes at the hangar, then hot starting for practice. Maybe I should put Don's number on my starting checklist :)

Thankfully the plane has two PC680 batteries, though I'd like to cut that down to a single lithium at some point. I need to learn how to crank it with only one battery first :)

Thanks,
Rusty
 
Do you have electronic ignition?
We have PMags and when we switched to automotive spark plugs, our hot start problems disappeared.

TIFWIW.

Left Mag, and right electronic. I leave them both on for start. Conditional is next month, so I'll be taking a close look at the plugs, since I'm not really sure what's in there. The plane originally had dual electronic, but one got swapped back to mag, which is probably how I prefer it.

Thanks,
Rusty
 
I've also found that getting the start process down pat (both hot and cold) using the Airflow Performance FI with purge valve has been a struggle using their recommendations.

For me this has been working great: Throttle halfway, Mixture rich, Purge valve ICO. Run the boost pump 30 seconds. Watch the fuel pressure come up and boost pump off. Purge Valve to Run, Throttle in about 1/4" in from Idle. (Basically this works the same for both hot/cold starts. You are just getting the cooler fuel to circulate up to the distribution spider.)

For cold starts: Run the boost pump about 5 seconds on/off to prime. Turn the key. (I found that originally I wasn't letting the boost pump run enough here, especially when it is cooler outside).

For hot starts: Mixture ICO. Turn the key. Slowly advance Mixture to rich. Be prepared to give the Throttle a push after it starts, and/or toggle the boost pump to make sure the fuel gets pushed into the cylinders. Sometimes here if the initial start doesn't take, give it full throttle while cranking.

I'm still trying different techniques to get this fool proof.
 
IMHO, DanH?s posts in the thread he referenced above bring common sense in the witch craft of hot starts we are trying to practice. I just want to make sure that reference doesn?t get overlooked.
 
Hot start discussions are right up there with politics and religion. Eventually there is going to be a fight.
For the record, I am 100% with Steve Rush (Arlington RV) on this one. As he stated above. No prime. Throttle barely cracked and mixture at idle cut off. While cranking slowly sweep the mixture from ICO towards rich until the engine fires and runs. You have just found the perfect stoichiometric mixture where the engine just starts running. None of this nonsense of running the fuel pump, putting in full throttle and mixture at idle cutt off and then swapping them back and forth before the engine dies method. How many hands do you have? I used to do that method too. And it's pure c***. As a repeated review: Just don't prime, crack the throttle and leave it be. Then as you crank smoothly slowly sweep the mixture from idle cutt off towards rich. No need to reach for the throttle.

It works a treat.

Jim
 
Hot start discussions are right up there with politics and religion. Eventually there is going to be a fight.
For the record, I am 100% with Steve Rush (Arlington RV) on this one. As he stated above. No prime. Throttle barely cracked and mixture at idle cut off. While cranking slowly sweep the mixture from ICO towards rich until the engine fires and runs. You have just found the perfect stoichiometric mixture where the engine just starts running. None of this nonsense of running the fuel pump, putting in full throttle and mixture at idle cutt off and then swapping them back and forth before the engine dies method. How many hands do you have? I used to do that method too. And it's pure c***. As a repeated review: Just don't prime, crack the throttle and leave it be. Then as you crank smoothly slowly sweep the mixture from idle cutt off towards rich. No need to reach for the throttle.

It works a treat.

Jim

Please elaborate on the purpose of the "sweep." My experience shows that there is only about 1/16" of travel where the mixture is between full rich for the idle circuit and too lean to support running at idle. You may have noticed this as well, when doing a test for your idle mixture (looking for a small rise in EGT as it starts going lean from full rich). I don't understand what the sweep is doing in your process. The idle mixture circuit, when properly adjusted, provides a perfect stochiometric mixture (actually richer than stochiometric typically provides a better idle) when the mixture is full rich and it maintains it until you pull the mixture back far enough that it reduces the flow below that which the idle circuit is set to deliver via the idle mixture screw.

Larry
 
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Morning,

This is starting to look like all the other old posts I read about the subject. I guess it's frustrating that there isn't one definitive best method, but rather a few similar but slightly different methods.

FWIW, here is the original checklist that came with the plane. This is the mixture method as recently described by a couple people. It has NOT worked well for me. I did later start moving the mixture knob slowly forward during cranking, but as someone else mentioned, the mixture is like an on/off switch it seems. After the first 1/4 of travel, it's essentially full rich. Maybe I need to go more slowly through that first 1/4 of travel.

Hot Start (Skip if cold)

1- Fuel Select- RT TK
2- Purge Valve- AFT
3- Throttle- FWD
4- Mixture- FWD
5- Pump SW- UP (35) - DOWN

Normal Start

1- Fuel Select- Fullest TK
2- Purge Valve- FWD
3- Throttle- 1/8 FWD
4- Mixture- AFT
5- Pump SW- UP (pressure)
6- Mixture- FWD (5 Cold, 1 Hot)- AFT
7- Pump SW- DOWN

8- EI & MAG SW- UP
9- Starter- PUSH
10- Mixture- FWD (when engine starts)


This is what appears to be the AP recommendation:

HOT STARTS
• Mixture control "FULL RICH".
• Throttle wide open.
• Purge valve "OFF" position.
• Turn on boost pump and let run 30 to 45 seconds. This will
purge the hot fuel and vapor from the system, and will cool and
fill the fuel system components with cool fuel.
• Leave the boost pump on.
• Set Throttle to 1/8 open.
• Give engine a short prime by putting the purge valve to “run”
then back to “off”.
• Leave Mixture control "Full Rich".
• With mags "HOT”, crank engine, when engine fires, return
throttle to idle and purge valve to “Run".

The two methods mainly seem to differ in how fuel is introduced. One uses the mixture control, and the other uses the purge valve. I have joked about not having enough hands to perform this method :)

I do appreciate all the comments. For now, I'm probably going to try the official method, with no prime. Next I might try the original mixture method, but making sure to sweep that first quarter of mixture travel more slowly.

Thanks,
Rusty
 
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Hot start discussions are right up there with politics and religion. Eventually there is going to be a fight.
For the record, I am 100% with Steve Rush (Arlington RV) on this one. As he stated above. No prime. Throttle barely cracked and mixture at idle cut off. While cranking slowly sweep the mixture from ICO towards rich until the engine fires and runs. You have just found the perfect stoichiometric mixture where the engine just starts running. None of this nonsense of running the fuel pump, putting in full throttle and mixture at idle cutt off and then swapping them back and forth before the engine dies method. How many hands do you have? I used to do that method too. And it's pure c***. As a repeated review: Just don't prime, crack the throttle and leave it be. Then as you crank smoothly slowly sweep the mixture from idle cutt off towards rich. No need to reach for the throttle.

It works a treat.

Jim

At places like OSH, Van's demo pilots are doing hot starts every 20 - 25 minutes, all day long after only about a 2 minute shut down.

This is basically the procedure taught to all Van's company pilots and the one that has been in use for 20+ years with good results.

A key to the procedure is moving the mixture slowly while cranking (3 - 4 seconds between ICO and mid range on the mixture travel) and as soon as it starts to fire, stop moving it.
 
I did later start moving the mixture knob slowly forward during cranking, but as someone else mentioned, the mixture is like an on/off switch it seems. After the first 1/4 of travel, it's essentially full rich. Maybe I need to go more slowly through that first 1/4 of travel.

If this were the case then the fwd half of the mixture control range would never even be used in flight but it is rare to pull the mixture beyond the midway point in flight when leaning.

My experience is that most of the time the start will happen when the mixture has been advanced to about the 1/2 way point (assuming a properly set up fuel delivery system.

Do you know for a fact that you idle mixture is adjusted correctly? If it is too rich it could make starts more difficult.
 
Greetings,

I continue to struggle with hot starts, even though the Airflow Performance system has a purge valve that's supposed to make this easier.

No prime. Throttle barely cracked and mixture at idle cut off. While cranking slowly sweep the mixture from ICO towards rich until the engine fires and runs.

I think the OP was asking how to utilize the purge valve in a hot start situation.

Jim's response is fine, but no mention of the purge valve.
 
I think the OP was asking how to utilize the purge valve in a hot start situation.

Jim's response is fine, but no mention of the purge valve.

Valid point, but Rusty's most recent post was only talking about the sweep method not working for him. Whether you have a purge valve or not should make no difference on whether the sweep procedure works during a hot start, it just might help it work better.

I only fly one airplane with an AFP system and a purge valve.
My understanding of its proper use (and the way I use it, but my understanding could be wrong) is to open the purge valve to shut the engine down, and then leave the purge valve open while the airplane is parked. This helps prevent fuel that gets heated and expands, from inducing system pressure and pushing fuel out the injectors while everything gets heat soaked while parked.

When it is time to start,
- Throttle wide open
- Turn on the boost pump for 10 - 15 seconds (with the purge valve still open) to flush heated fuel from the system.
- Turn off the boost pump
- Close the purge valve
- pull mixture to ICO
- pull throttle to 1/8" open
- Do a normal start using the mixture sweep procedure. Starts every time.
 
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A key to the procedure is moving the mixture slowly while cranking (3 - 4 seconds between ICO and mid range on the mixture travel) and as soon as it starts to fire, stop moving it.

Hi Scott,

This may indeed by the key. The procedure has been in the aircraft checklists though every owner as far as I can tell, but what's not stated is how slowly to move the mixture. That little detail may be the missing piece of the puzzle.

BTW, Idle mixture is correctly adjusted, and I can move the mixture from full rich (100%) to about 25% in flight with no measurable change. I suspect maybe something in the system isn't sized correctly, and it's on the list of things to sort out eventually, once I get the bigger issues sorted, and if I haven't gone to EFI by then :)

Cheers,
Rusty
 
BTW, Idle mixture is correctly adjusted, and I can move the mixture from full rich (100%) to about 25% in flight with no measurable change. I suspect maybe something in the system isn't sized correctly, and it's on the list of things to sort out eventually, once I get the bigger issues sorted, and if I haven't gone to EFI by then :)

Cheers,
Rusty

This may be a good part of your problem.
The IO-320 airplane I fly with an AFP fuel system is at about the ~50% point in mixture travel when slightly lean of peak in cruise.

One possible cause is that the mixture arm on the throttle body might be set up wonky which could make most of the arm travel happen during the last bit of control travel.
The ideal geometry is for the arm to be perpendicular to the control at the mid point of its travel range.
 
None.

You are most likely idling at shutdown, which is a happy place for both the mixture and throttle. Just use the bypass valve to shut the engine down, not the mixture.

For restart, with the bypass still open, turn on the boost pump while you get buckled in, boot up the EFIS etc. Throttle and mixture still where you had them at shutdown.

Now start cranking and slowly close the bypass. Boost pump off after start.

This is what I used in my 10-----worked well for me.

This works for me also. Always starts.
 
This may be a good part of your problem.
The IO-320 airplane I fly with an AFP fuel system is at about the ~50% point in mixture travel when slightly lean of peak in cruise.

One possible cause is that the mixture arm on the throttle body might be set up wonky which could make most of the arm travel happen during the last bit of control travel.
The ideal geometry is for the arm to be perpendicular to the control at the mid point of its travel range.

Interesting. I'll put that on the list of things to check. I know the arm moves from stop to stop with the full range of the mixture cable, but if the arm can be repositioned on the shaft, that could be part of the reason.

I had also wondered if maybe the injector nozzles were bigger than they should be, or something like that. I may have to buy a new manual from AP since part of this one is missing, and the rest is pretty ratty. At least it runs well when I can crank it.

Cheers,
Rusty (almost certainly the cause of the hot start problem)
 
A "sweep" does not necessarily involve movement of the mixture control. It merely describes any approach which cycles in-cylinder mixture from rich to lean or lean to rich over the course of several crankshaft revolutions.
Flooding the engine with prime, then cranking with throttle at WOT and mixture at ICO is a.good.example. With each gulp of.air, in-cylinder mix moves progressively from too rich toward too lean. At some point it sweeps through the sweet spot.
 
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A "sweep" does not necessarily involve movement of the mixture control. It merely describes any approach which cycles in-cylinder mixture from rich to lean or lean to rich over the course of several crankshaft revolutions.
Flooding the engine with prime, then cranking with throttle at WOT and mixture at ICO is a.good.example. With each gulp of.air, in-cylinder mix moves progressively from too rich toward too lean. At some point it sweeps through the sweet spot.

You are of course correct....
In the posts where I used the term sweep it should have said "control sweep procedure"

Still the much more appropriate procedure than risking a start at WOT, in my opinion.
 
I would like to ask the question: What constitutes a hot restart? Is it a hot restart if and only if the engine has already attained its normal operating temperature?

In my own case, AFP injection system on an ECI Titan IOX-370 with 2 P-Mags, I find that almost no priming is necessary when the engine is cold (1 second of prime is what I use). And when hot, any priming at all will make for a difficult restart. I do not have a recirculating fuel system.

My hot start procedure is very similar to what has already been described:
1. Throttle just barely cracked open.
2. Mixture at ICO.
3. Crank -- and when the engine first fires, stop cranking and (quickly) move the mixture to its normal idle position.

This process has always produced quick, smooth restarts even under high ambient temperatures. But it begs the question: How does one know when it is best not to prime? How long must the plane sit idle before switching back to the cold start procedure?

Additional data point: I have learned that using my "hot start" procedure produces the best results anytime the engine has been running for more than a couple of minutes. Even when I know that it has not yet reached its nominal operating temperature.
 
I would like to ask the question: What constitutes a hot restart? Is it a hot restart if and only if the engine has already attained its normal operating temperature?

In my own case, AFP injection system on an ECI Titan IOX-370 with 2 P-Mags, I find that almost no priming is necessary when the engine is cold (1 second of prime is what I use). And when hot, any priming at all will make for a difficult restart. I do not have a recirculating fuel system.

My hot start procedure is very similar to what has already been described:
1. Throttle just barely cracked open.
2. Mixture at ICO.
3. Crank -- and when the engine first fires, stop cranking and (quickly) move the mixture to its normal idle position.

This process has always produced quick, smooth restarts even under high ambient temperatures. But it begs the question: How does one know when it is best not to prime? How long must the plane sit idle before switching back to the cold start procedure?

Additional data point: I have learned that using my "hot start" procedure produces the best results anytime the engine has been running for more than a couple of minutes. Even when I know that it has not yet reached its nominal operating temperature.

If it's not the first start of the day I always use my hot start procedure. (mixture lean, throttle cracked, increase mixture on first fire). This includes when I start after the 1/4 mile taxi to the fuel pump, so not anywhere near operating temp. If it doesn't pop by 5 or so seconds of turning over, I would stop and prime; but I've never had to do that.
 
You are of course correct....
In the posts where I used the term sweep it should have said "control sweep procedure"

We're on the same page Scott. I was responding to post 13.

Still the much more appropriate procedure than risking a start at WOT, in my opinion.

Absolutely. I treat the WOT-ICO rich-to-lean method as secondary, if I manage to somehow foul up the throttle cracked lean-to-rich sweep.
 
Absolutely. I treat the WOT-ICO rich-to-lean method as secondary, if I manage to somehow foul up the throttle cracked lean-to-rich sweep.

WOT-ICO is intended to keep MAP high for good easy airflow while cutting off the fuel - but at cranking speed WOT is not needed for that, a cracked throttle appropriate for 900-1000 rpm will suffice just fine without the danger of a WOT start.
 
If this were the case then the fwd half of the mixture control range would never even be used in flight but it is rare to pull the mixture beyond the midway point in flight when leaning.

My experience is that most of the time the start will happen when the mixture has been advanced to about the 1/2 way point (assuming a properly set up fuel delivery system.

Do you know for a fact that you idle mixture is adjusted correctly? If it is too rich it could make starts more difficult.

The mixture knob controls gross flow into the servo. At full rich, it will flow somewhere around 16+ GPH and at ICO it will flow 0 GPH. It is pretty linear from Full rich to ICO. The downstream parts of the servo deliver what they feel is appropriate for any given airflow and vacuum condition, assuming that level of flow is available from the gross flow control (flow can only be limited, not added via this flow contol). At around 1000 RPM, where we usually start our engines, your idle circuit typically flows around 1.5-2 GPH. In cruise, you're probably flowing 8 GPH, so the mixture knob would be in different positions to deliver a maximum of 2 vs 8 GPH.

I am not saying that your procedure is inappropriate or wrong, just trying to illuminate the cause and effect related to the mixture knob.
 
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A "sweep" does not necessarily involve movement of the mixture control. It merely describes any approach which cycles in-cylinder mixture from rich to lean or lean to rich over the course of several crankshaft revolutions.
Flooding the engine with prime, then cranking with throttle at WOT and mixture at ICO is a.good.example. With each gulp of.air, in-cylinder mix moves progressively from too rich toward too lean. At some point it sweeps through the sweet spot.

got it and agree.
 
at ICO it will flow 0 GPH. I

Are you sure of this?

IIRC, the Airflow Perf units still flow a small amount at full lean on the mixture----one of the reasons for the purge valve being used to shut down the engine.
 
This is true of the FM-200 but not the FM-150 which cuts the flow completely. For the 150, a purge valve is not required, but is handy for hot starts.

Ed Holyoke

Are you sure of this?

IIRC, the Airflow Perf units still flow a small amount at full lean on the mixture----one of the reasons for the purge valve being used to shut down the engine.
 
OK, got that.

Pretty sure I had the 200 on my IO540.

Memory fades a bit ------ 11+ years old info from when I got the engine.
 
Are you sure of this?

IIRC, the Airflow Perf units still flow a small amount at full lean on the mixture----one of the reasons for the purge valve being used to shut down the engine.

Sorry Mike. I am only familiar with the Bendix and assumed the AFP was the same. If the mixture control doesn't go to 0 or close to it, you can't stop the engine via fuel flow; At least without another cutoff somewhere else. I imagine that the purge valve must be required for that model servo that doesn't fully close.

Larry
 
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