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07-13-2015, 07:22 PM
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Join Date: Jan 2008
Location: Des Moines, IA
Posts: 62
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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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07-13-2015, 07:46 PM
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Join Date: May 2014
Location: Savannah
Posts: 806
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Check for intake leaks.
__________________
Mike Hammond
A&P IA PPL ASEL
RV-14A kit S/N 140170
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07-14-2015, 07:54 AM
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Join Date: Oct 2006
Location: Garden City, Tx
Posts: 5,145
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Sounds like classic vapor lock to me.
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Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2020 dues paid 
N16GN flying 700 hrs and counting; IO360, SDS, WWRV200, Dynon HDX, 430W
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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07-14-2015, 10:56 AM
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Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,686
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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.
__________________
Walt Aronow, DFW, TX (52F)
EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 1700+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154
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07-14-2015, 12:21 PM
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Join Date: Mar 2008
Location: Ramona, CA
Posts: 2,370
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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.
Last edited by bruceh : 07-17-2015 at 11:03 AM.
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07-14-2015, 01:18 PM
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Join Date: Oct 2006
Location: Garden City, Tx
Posts: 5,145
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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.
__________________
Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2020 dues paid 
N16GN flying 700 hrs and counting; IO360, SDS, WWRV200, Dynon HDX, 430W
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
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07-14-2015, 01:35 PM
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Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,686
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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.
__________________
Walt Aronow, DFW, TX (52F)
EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 1700+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154
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07-15-2015, 07:03 AM
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Join Date: Jun 2006
Posts: 316
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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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07-15-2015, 11:20 PM
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Join Date: Nov 2008
Location: Kansas City, MO
Posts: 120
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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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07-16-2015, 06:47 PM
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Join Date: May 2005
Location: San Ramon, CA
Posts: 402
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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.
__________________
Michael Wynn
RV8 Phase II
Livermore, CA
2017 Dues Paid
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