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RV-List: Lycoming Engine Fuel Flow Problem...

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PostPosted: Wed Nov 18, 2015 8:29 pm    Post subject: RV-List: Lycoming Engine Fuel Flow Problem... Reply with quote

After ruling out visible leakage and ensuring the mixture cable gives
full mixture range motion (to the stop on the carb), I think I'd
disconnect the fuel hose right before the carb and use the boost pump to
see the max available fuel flow rate to the carb. That could give you
some insight into blockages prior to the carb. This test (fuel flow
volume) is described in the old FAA Experimental Aircraft Flight Test AC
on page 23 (AC 90-89A, available at
FAA recommends seeking 125% of normal max fuel flow (and they tell you
how to estimate that value).



Tim Lewis -- HEF (Manassas, VA)
RV-6A N47TD -- 1104 hrs - sold
RV-10 N31TD -- 650 hrs

Matt Dralle wrote on 11/17/2015 10:24 PM:

Dear Listers,

I flew the RV-6 tonight that has a 1660 hour Lycoming O-360A1A with a Hartzell CS prop. I flew it 7 hours over a 3-day period about a week and a half ago with no issues whatsoever. Tonight, on take off, the EGT's all climbed into the 1450's right after take off and the CHT's were in the 400-450 range. The mixture was full rich. The engine didn't seem to be underpowered or rough but the fuel flow was about 9-10 GPH when it should have been in the 17-19GPH range. On the downwind I tried fiddling with the mixture with no change in making it richer. The mixture did make it leaner. I switched from the right to the left fuel tanks with no change. I have two fuel flow transducers one feeding the Skyview and the other feeding a Matronics FuelChec DX. Both were reading similarly low fuel flows at full throttle - 9-10gph. I didn't think to flip on the electric boost pump. But the flow definitely seemed restricted. The mixture control seems to have normal throw in and out a!
nd isn't binding and does lean the engine. I came in and landed with no issues.

I haven't pulled the cowling yet to have a look to see if its something obvious with the mixture cable, but what are some thoughts on what this could be?

Mechanical Fuel Pump?

Something in the Carb?

Plugged fuel line?


Thanks for your feedback,


Matt Dralle

RV-8 #82880 N998RV "Ruby Vixen" - Matt's Complete RV-8 Construction Log - Landing Mishap Rebuild Log - Matt's RV-8 HDTV YouTube Channel
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Status: 350+ Hours - Full Flyer Mode!

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