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  #11  
Old 08-06-2017, 08:08 AM
n982sx n982sx is offline
 
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Quote:
Originally Posted by DanH View Post
a successful start procedure finds the sweet spot by sweeping fuel-air ratio through a range of mixtures while cranking
This is how I have always thought of it.

So far I have used the Lycoming manual procedures without fail or sweat. One thing not mentioned here so far is their reference to exactly how much to prime in a cold start. They call for priming until the FF reaches 4 gph then pull mixture to ICO.

This seems to me to account for the differences in fuel pump rates or pressures.

I also believe it it important to get the idle mixture set correctly. As Tim Olsen mentioned in one of his threads the idle mixture seems to come set on the rich side from the factory. I found this to be true and on mine, it was very rich.

Starting takes place in the throttle range were this setting accounts for a lot of the fuel flow to the engine. Leaving it too rich could have an adverse effect on starting.
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  #12  
Old 08-13-2017, 10:04 AM
Adriaan Kleyn Adriaan Kleyn is offline
 
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I have found the problem, and she starts like magic now,hot or cold. It was strange to me that it only starts when you leaves the key and not while the starter is engaged ( if she starts ). On the ignition there are to ground positions. The one is for both magneto's and the other one is only for the right magneto. When you engage the starter it grounds the right magneto so that only the left magneto with the impulse fires. The problem was that the ground was on the left magneto so the wrong magneto was grounded when the the starter was engaged. I have swop the ground wire and the problem is solved.
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  #13  
Old 08-13-2017, 03:14 PM
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Originally Posted by rvbuilder2002 View Post
With the first (RV-14A) prototype, we learned after some initial struggles, that the Andair fuel pump is a very high volume flow pump.

Any RV model equipped with the Andair pump will require a change in priming technique from what people have always used / learned.

First start of the day in warmer weather I put throttle and mixture full fwd and run the pump for about 1 second
I don't get it: What does the throttle position have to do with priming a F/I engine? What does a fuel injector care whether the butterfly is open or closed while priming?

~Marc
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  #14  
Old 08-13-2017, 06:08 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Originally Posted by Plummit View Post
I don't get it: What does the throttle position have to do with priming a F/I engine? What does a fuel injector care whether the butterfly is open or closed while priming?

~Marc
Do some reading on the way mechanical fuel injection works.

The throttle arm on the servo / throttle body opens and closes the throttle plate (butterfly) and controls a fuel pressure regulator within the servo that varies the fuel pressure in the fuel line that links to the distribution manifold on the top of the engine.
This variable fuel pressure is what regulates the amount of fuel that flows out of the constant flow injectors.
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  #15  
Old 08-13-2017, 10:27 PM
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Originally Posted by rvbuilder2002 View Post
Do some reading on the way mechanical fuel injection works.

The throttle arm on the servo / throttle body opens and closes the throttle plate (butterfly) and controls a fuel pressure regulator within the servo that varies the fuel pressure in the fuel line that links to the distribution manifold on the top of the engine.
This variable fuel pressure is what regulates the amount of fuel that flows out of the constant flow injectors.
I did do some reading Scott, and what I read is pretty specific that AIRFLOW through the servo determines how much fuel is released to the flow divider. If the engine is not running, there is no airflow through the servo. It doesn't matter what position the throttle plate is in.

My RV-10 has an AFP fuel system, which Don says is the same basic system as Bendix.

From the AFP manual: "The FM-series fuel injection system uses the proven principal of mass airflow metering to proportion the fuel flow to the engine.
The FM-series system is a mass airflow device employing a venturi to generate a signal corresponding to the mass airflow..."

So if there is no airflow (as when priming a non-running engine), what difference does it make if the throttle plate is open or closed?

-Marc
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  #16  
Old 08-13-2017, 10:56 PM
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erich weaver erich weaver is offline
 
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I'm guessing Scott knows what he is talking about here. The AFP instructions for cold starting that I have indicate to prime with the throttle in for a few seconds and then pull it out to idle before starting. Works well. Not so well when i prime with the throttle out. There is clearly something going on here other than airflow

Erich
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  #17  
Old 08-14-2017, 08:08 AM
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Plummit Plummit is offline
 
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Default Lycomings instructions

From the Lycoming page:

https://www.lycoming.com/content/tips-start-your-engine

"Most Lycoming fuel-injected engines are simply primed by turning the fuel boost pump on, opening the mixture briefly to full rich, and cracking the throttle. Any pumping of the throttle is ineffective until the engine begins to fire."

When I start my engine I go mixture rich, throttle cracked (only because I want to start it at idle with some air), fuel pump on and bypass valve in for 5 seconds to prime.

-Marc
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  #18  
Old 08-14-2017, 08:45 AM
rvbuilder2002 rvbuilder2002 is offline
 
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On a Bendix style servo the throttle arm has a mechanical connection to a control valve.

When the throttle arm moves between idle and WOT, it is changing the position of this valve.

The linkage to this valve is adjusted to change idle mixture (rate of fuel delivery by the injectors).

I never meant to imply that said valve was the only control of fuel delivery.... just that it does have an influence on the amount of delivery.
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