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09-09-2012, 01:31 PM
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Join Date: Jan 2005
Location: Yorkshire, England
Posts: 2,052
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Hot Rough Running
I'm noticing after a fuel stop, when I restart the engine it hesitates, surges and nearly quits. Runs like a bag of spanners - sorry, wrenches.....
Power check clears it and on take off, no problem.
I can't decide whether it is fuel vapour locking or a problem with hot P-Mags.
Any suggestions gratefully received
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"I add a little excitement, a little spice to your lives, and all you do is complain!" - Q
Donated in 2020
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09-09-2012, 01:37 PM
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Join Date: Feb 2005
Location: Huskerland, USA
Posts: 5,862
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It would help if we knew what plane, engine, and fuel system you have, and what fuel you are burning. 
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RV-7 : In the hangar
RV-10 : In the hangar
RV-12 : Built and sold
RV-44 : 4 place helicopter on order.
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09-09-2012, 01:52 PM
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Join Date: Jan 2005
Location: Yorkshire, England
Posts: 2,052
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Sorry,
Used to be on my signature but I changed it.
RV7
Mattituck ECI motor, TMX IO-360, dual P-Mags, Silverhawk Fuel Injection.
Would never consider anything other than Avgas.......
The temperature spots on the P-Mags haven't gone black.
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"I add a little excitement, a little spice to your lives, and all you do is complain!" - Q
Donated in 2020
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09-09-2012, 01:55 PM
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Join Date: Jan 2005
Location: Indiana
Posts: 270
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Vapor Lock
Sounds like fuel vapor lock.
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09-09-2012, 02:04 PM
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Join Date: May 2006
Posts: 16
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Try leaning your mixture after startup. Not sure your location but I'm at 5000' and have to lean every time I stop for fuel. I also have the Silver Hawk system.
Ron B
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09-09-2012, 02:07 PM
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Join Date: Aug 2008
Location: Sun city, Ca.
Posts: 255
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I have pretty much the same setup and mine does the same thing. Don't think it would ever stop running, but sure not the same smooth sound. Also does it after landing towards the end of a long taxi while really leaned out. I've just assumed its the slow moving fuel in the injector lines getting too hot and boiling.
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09-09-2012, 02:36 PM
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Join Date: Jan 2005
Location: 57AZ - NW Tucson area
Posts: 10,011
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Quote:
Originally Posted by RonB
Try leaning your mixture after startup. Not sure your location but I'm at 5000' and have to lean every time I stop for fuel. I also have the Silver Hawk system.
Ron B
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Highest spot in England is only 3200 ft.
And it's a nice hike up - Scafell Pike.
__________________
Gil Alexander
EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ
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09-09-2012, 03:20 PM
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Join Date: Dec 2005
Posts: 976
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Quote:
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I can't decide whether it is fuel vapour locking or a problem with hot P-Mags.
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fuel vapour locking IMHO.
Fuel Pump on will help a bit...
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09-09-2012, 04:13 PM
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Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,686
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If it was actual "vapor lock" no fuel would be getting to the servo and the engine would quit (vapor lock occurs prior to the engine pump and blocks fuel flow).
I think the most likely cause is fuel boiling in the fuel injector lines and fuel distribution manifold. This is a common problem on most FI engines on a quick-turn (especially in hot climates). Not much you can do about it unless you want to add a purge valve (circulates cool fuel up the to the manifold), or as you have done, clearing with some extra power to purge the hot fuel.
Just my 2c
__________________
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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09-09-2012, 05:56 PM
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Join Date: Oct 2006
Location: Tauranga New Zealand
Posts: 26
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IMO Boiling fuel in the injector lines.
I have an IO-360. With dual P Mags. Runs well when cold but after flight and or a long taxi, engine runs with lots of missing and sounds terrible, to fix, apply power once the fuel starts flowing the missing seems to reduce BUT it won?t go away until full power for takeoff, that fixes it quickly.
FWIW Just after shut down the top of my cowl is nice and cool to touch but give it 5 minutes and you could fry eggs on it. The bottom cowl stays cool, inside, the exhaust is less than 1 inch away from the bottom cowl but you would never know it. I guess this just proves hot air rises and all this heat is boiling up those little fuel lines on top of the engine. I believe the fuel pressure in these lines is around 4psi and there is not much flow at idle so I think this is the reason for the rough running. I have got used to it now and don?t worry about it. I also open my oil door after shut down to let as much hot air out from behind the engine where my P mags are.
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Bruce Black
New Zealand
RV6 finished and flying.
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