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  #11  
Old 02-19-2018, 07:56 PM
Kalibr Kalibr is offline
 
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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.
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  #12  
Old 02-19-2018, 09:22 PM
jliltd jliltd is offline
 
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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
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  #13  
Old 02-19-2018, 11:17 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by jliltd View Post
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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Last edited by lr172 : 02-19-2018 at 11:33 PM.
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  #14  
Old 02-20-2018, 05:11 AM
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13brv3 13brv3 is offline
 
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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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Last edited by 13brv3 : 02-20-2018 at 05:13 AM.
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  #15  
Old 02-20-2018, 09:10 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by jliltd View Post
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.
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  #16  
Old 02-20-2018, 09:15 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by 13brv3 View Post
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.
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  #17  
Old 02-20-2018, 09:23 AM
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Mike S Mike S is offline
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Quote:
Originally Posted by 13brv3 View Post
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.
Quote:
Originally Posted by jliltd View Post
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.
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  #18  
Old 02-20-2018, 09:55 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by Mike S View Post
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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RV-6A (aka "Junkyard Special ")

Last edited by rvbuilder2002 : 02-20-2018 at 10:30 AM. Reason: fixed order steps that I messed up with cut and paste
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  #19  
Old 02-20-2018, 10:18 AM
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13brv3 13brv3 is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post

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
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RV-3B, SN-11351, purchased, , flown, sold
A&P - 2018
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  #20  
Old 02-20-2018, 10:28 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by 13brv3 View Post
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.
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