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  #1  
Old 07-13-2015, 07:22 PM
CopterJohn CopterJohn is offline
 
Join Date: Jan 2008
Location: Des Moines, IA
Posts: 62
Default Solving the mixture issue.

I am 36 hours into my 40 hour test period on my 0-360 with airflow performace injection package. Setup mixture initially last fall for 30 rpm increase at cutoff per Lycoming SB. Ran perfectly until a few days ago.

Now that it is hot out, the engine is barking and coughing at idle after a test flight and tries to keep running when the mixture is pulled.

We reset the mixture again today on a warm engine and it idled smoothly with the proper increase at fuel cutoff. Cowled it up, went flying, and came back to have the engine quit in the flare when the throttle was retarded to 890 rpm. Withe the Whirlwind, the prop stops dead.

Had to use the flooded start technique to get it going and taxi in. Quit again at the hangar when the throttle is pulled back with mixture in.

What now? Is this a heat or vapor lock issue we are chasing?
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  #2  
Old 07-13-2015, 07:46 PM
Mike H Mike H is offline
 
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Location: Savannah
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Default

Check for intake leaks.
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  #3  
Old 07-14-2015, 07:54 AM
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airguy airguy is offline
 
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Location: Garden City, Tx
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Default

Sounds like classic vapor lock to me.
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  #4  
Old 07-14-2015, 10:56 AM
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Walt Walt is offline
 
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Location: Dallas/Ft Worth, TX
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Default

Sounds pretty normal to me... the AFP systems (as well as most Bendix) suffer from poor idle with the hot under cowl temps in the summer, low fuel flow thru the injector lines and FDM (spyder) will cause rough running at idle.

I would suggest you go back and set the mixture with the engine cold/warm (not hot) then leave it alone.

The AFP does not cut off fuel 100% like the bendix does, I take it you don't have the purge valve which is normally used for shutdown.
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  #5  
Old 07-14-2015, 12:21 PM
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bruceh bruceh is offline
 
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Location: Ramona, CA
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Default

I've got similar issues with AFP and idling when hot. It is boiling fuel in the steel tubing going to the injectors, and I've messed around a bit with the lean idle mixture settings to no avail. I've found that as long as I keep the RPM's up around 950-1000, it runs fine when hot. Below 850-900 it starts to stumble. It idles fine when cooler at those lower RPM's. I've also got the composite lightweight prop, which doesn't help.
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Last edited by bruceh : 07-17-2015 at 11:03 AM.
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  #6  
Old 07-14-2015, 01:18 PM
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airguy airguy is offline
 
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It's going to come down to keeping the FWF fuel as cool as possible, insulate what you can with firesleeve and put a blast tube on the fuel pump.
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Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2020 dues paid
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Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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  #7  
Old 07-14-2015, 01:35 PM
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Walt Walt is offline
 
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This is not "vapor lock", vapor lock occurs on the inlet (low pressure) side of a pump at high temps due to fuel boiling, this condition is just the boiling of fuel in the fuel distribution manifold and FI lines to the nozzles (due to the low pressure in the FI lines at idle). That's why it clears up immediately at higher power settings.
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  #8  
Old 07-15-2015, 07:03 AM
Don at Airflow Don at Airflow is offline
 
Join Date: Jun 2006
Posts: 316
Default fuel boiling?

Without knowing what model of fuel injection is on the engine or the installation you might want to give us a call to discuss your options.

We have two different regulator systems. One uses the purge valve for hot start fuel circulation and engine shut down. This is because this model regulator uses rotary idle and mixture control valves. Thus ICO is not zero leak on this model. The other model regular uses a different design fuel regulator. This model has a zero leak mixture control so most installations do not use the purge valve. This is standard on the FM-150, FM-150L and FM-250, but is also used on the FM-100A, FM-200A, and FM-300B.

You made a comment that the engine ran well for over 30 hours and just recently started having idle issues. So were the temperatures in those previous flights any hotter than the last few hours. If not then it?s possible that you have some other issue than boiling fuel in the nozzle lines.

At this point we need much more information about your installation and system than is described in the first post.


Don
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  #9  
Old 07-15-2015, 11:20 PM
N54SG N54SG is offline
 
Join Date: Nov 2008
Location: Kansas City, MO
Posts: 120
Default

And just for the record, I can idle all day when hot at 800 RPM with my FM-200A. That is the unit without the return line.

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  #10  
Old 07-16-2015, 06:47 PM
mlwynn mlwynn is offline
 
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Location: San Ramon, CA
Posts: 402
Default Rough Idle

Do you have a sniffle valve? I started with one. It got clogged (open) and caused all kinds of grief till I figured out the problem.
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