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  #21  
Old 02-20-2018, 10:56 AM
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Geico266 Geico266 is offline
 
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Quote:
Originally Posted by Mike S View Post
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.
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  #22  
Old 02-20-2018, 10:59 AM
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Originally Posted by rvbuilder2002 View Post
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)
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  #23  
Old 02-20-2018, 11:35 AM
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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.
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Last edited by DanH : 02-20-2018 at 11:40 AM.
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  #24  
Old 02-20-2018, 11:57 AM
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Quote:
Originally Posted by DanH View Post
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.
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  #25  
Old 02-20-2018, 06:37 PM
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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.
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  #26  
Old 02-20-2018, 06:45 PM
odens_14 odens_14 is offline
 
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Quote:
Originally Posted by joe_rainbolt View Post
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.
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  #27  
Old 02-21-2018, 06:15 AM
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Quote:
Originally Posted by rvbuilder2002 View Post
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.

Quote:
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.
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  #28  
Old 02-21-2018, 07:53 AM
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Quote:
Originally Posted by DanH View Post


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.
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  #29  
Old 02-21-2018, 01:05 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
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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Last edited by lr172 : 02-21-2018 at 01:09 PM.
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  #30  
Old 02-21-2018, 01:11 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by DanH View Post
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.
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