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  #11  
Old 09-18-2017, 05:02 PM
kaa kaa is offline
 
Join Date: Dec 2013
Location: Oakland
Posts: 31
Default

Quote:
Originally Posted by RFSchaller View Post
Julian, was there any spiking of fuel flow or pressure that might indicate vapor lock?

Am I reading the graph right when it looks like your MAP is dropping? Is it a cause or an effect of the loss of power. I can't figure out what would cause it to drop as a cause unless the air flow was some how restricted and that doesn't seem feasible.

Rich
I have the same question - I don't understand how a fuel flow obstruction could cause such a remarkable drop in manifold pressure. It is my understanding that a loss of RPM due to fuel or spark should cause a rise in MP (the same way it behaves when you cycle a constant speed prop during runup).

UPD: oops, forgot it's turbocharged.

Last edited by kaa : 09-18-2017 at 05:04 PM.
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  #12  
Old 09-18-2017, 05:13 PM
Berchmans Berchmans is offline
 
Join Date: Nov 2009
Location: Anchorage, Alaska
Posts: 395
Default Engine Stumble

I had a problem with engine stumbling that did not show up during any run ups or such...turned out I had a couple intermittent bad plug wires...might not be a carb problem. Only showed up in cruise flight after several minutes in the air.
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  #13  
Old 09-18-2017, 06:50 PM
newamiga newamiga is offline
 
Join Date: Jan 2011
Location: Colorado Springs, CO
Posts: 174
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Guys,
I own an S-LSA with a 912 that I fly on long cross countries fairly frequently. I have experienced stumbles several times over the past couple years. Most recently on my trip to OSH this year, I ended up having to abort and return to my home airport because the stumbling got to the point that I thought I may have to make an off airport landing. My mechanic took everything apart and cleaned it all out, changed the fuel filter and it seemed to run fine. I flew it in the AirVenture Cup race and into Fond du Lac and parked it for the week of the show. On pre-flight to leave, I found the right carb literally leaking gas out the back of the carb and the scat hose that goes to the airbox. I left the plane on the ground and had the guys from Leading Edge Airfoils come up from the Milwaukee area come up and take the carb off, replace all floats, do the complete rebuild with all new parts and replace all hoses. It ran great on the flight home from there to New York.

Bottom line is that despite the fact that I had replaced the floats per the SB earlier, the new floats were actually bad as tested by the LEAF guys. My inclination is to say it is a float related issue.

Carl
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  #14  
Old 09-19-2017, 12:00 AM
Azjulian Azjulian is offline
 
Join Date: Dec 2015
Location: Scottsdale, Arizona
Posts: 123
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I have the carb stripped down on the bench, going through everything very carefully right now.

I'll update towards end of the week, when I've had a chance to do the work

I did measure the floats and they are good

I'm running 100LL have been since the issues started just to ensure a good fuel supply.
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  #15  
Old 09-19-2017, 06:13 AM
jdelpeso jdelpeso is offline
 
Join Date: Mar 2006
Posts: 32
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I experienced the same problem but with a low fuel pressure and hi fuel flow.
Changing the engine fuel pump solved the problem.
Jose del Peso 120633
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  #16  
Old 09-19-2017, 11:08 PM
RFSchaller RFSchaller is offline
 
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 2,132
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Julian,

If you take the plane to Roger and need a ride back from Marana or you'd like a ride down and back to drop off your carbs give me a call.

I'd loan you mine, but I just spent two months and big $ getting them right, and they have AN fuel fittings as opposed to the banjo fittings.

Rich
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  #17  
Old 09-21-2017, 12:52 AM
waterboy2110 waterboy2110 is offline
 
Join Date: Jul 2010
Location: SF Bay Area
Posts: 210
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Don't look past the restrictor that was removed from the return line. I've been told this solved several rough running engine problems. Rotax has it in there for a reason.
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  #18  
Old 09-21-2017, 08:57 PM
RFSchaller RFSchaller is offline
 
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 2,132
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Not directly related so forgive me if this is thread drift.

During my recent carburetor woes with the shop swapping my choke assemblies I came across a blog by a Brit ROTAX Repair shop that suggested adjusting the idle mixture screw to 2 turns from full clockwise as opposed to 1 1/2 turns gives a smoother idle. Has anybody tried this, and if so did it work?
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  #19  
Old 09-21-2017, 09:07 PM
Azjulian Azjulian is offline
 
Join Date: Dec 2015
Location: Scottsdale, Arizona
Posts: 123
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Iíve checked the return both by validating the hose is correct and that return fuel is seen in the filler neck.

I am running 100LL to help eliminate fuel contamination.

Hopefully I will be able to clean and test tomorrow.
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  #20  
Old 09-21-2017, 09:08 PM
Azjulian Azjulian is offline
 
Join Date: Dec 2015
Location: Scottsdale, Arizona
Posts: 123
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Thanks for the offer on going to see Roger Rich, Iíll let you know !
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