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Power Loss

Stan Bahrns

Active Member
Anyone having moderate power loss during flight? Initially on takeoff the power is normal but have had some power loss shortly after getting off the ground. I thought it was something in the carburetors but after taking them apart I found nothing. Fuel flow is good, could it be a electronic ignition problem? The mags both check the same, Just looking for another idea.
Thanks Stan
RV12 60 hrs
 
Joe is right. If you have the original model fuel pump (prior to later model with hose drain) you may have one of the bad ones.

I had partial power loss after rotation, was able to hold 4,000 RPM for the circuit to land. Happened twice. Dynon printout showed big fuel flow fluctuations to the down side. New pump solved it.

Jim
flying 330 hours
 
Loss of power but no fuel pump problem indicated from Dynon Data Log

I recently had a 600 rpm drop shortly after take off with my 912ULS. The engine is installed in my RV-12 which I built and have been flying for 5 years (245 hrs). I have done all the 5 year replacement items including fuel hoses,coolant hoses, carb sockets, sending Carburetors off for 200 hr service and 5-Yr rubber replacement, and Carbs balanced. I landed and could not get over 4,400 rpm WOT. Defueled the premium auto fuel and re-fueled with Av fuel. After running the Av fuel for a few minutes I could get the 5,000+ rpm and launched to my home airfield. I had an intermediate stop due to weather. On run up after intermediate stop I could not get over 4,400 rpm WOT. The following day I removed the carb bowls and weighed the floats.Each pair were under 7 grams. Saw not contamination. Installed floats and carb bowls and got 5,000+ rpm. Flew to home base without any further problems. Have flown 4 flights (2.5 hrs tot) within gliding range of AP without problems. I downloaded my Dynon 180 data file which shows an egt temperature difference of over 100 deg to as high as 130 deg for most of the time after the engine rpm drop. The data log for my intermediate flight of 0.9 hr flight after changing to Av gas indicates a more than 100 deg egt temperature difference for 0.56 hrs of the flight. the max temp diff was 195 deg (1,174 Lt/ 1369 Rt).EGT probes installed per plans. Current test flights show less that 85 deg egt temp difference. I have the new fuel pump which I installed less than 2 years ago at 164 hrs. The fuel pressure varied from 4.5 to 5.6 psi for all the flights. Since I have not found a smoking gun I am not sure if my problem has disappeared and I am reluctant to trust the engine. Any comments or suggestions appreciated. Bob Kibby N712BK
 
Assuming you didn't modify the system to turn off the electrical fuel pump (as I did) how do you pin this on the mechanical pump?
 
Loss of power but no fuel pump problem indicated from Dynon Data Log

If the last post was for N712BK I didn't suggest that problem was the fuel pump. On the contrary I was trying to say that the fuel pump was not the problem. My electric fuel pump is on when the Master Switch is On. Difference between the fuel pressure with the electric fuel is on the ground about +0.5 psi . I have never turned off the electric fuel while airborne. 2BK
 
Bob Kibby, check the download data for the specific time of the power loss, looking at all the pertinent columns for irregularities. If you can do an incident-free takeoff and compare download data, there might be clues. Would be best if ambient temperatures matched, too.

FWIW, both my power loss episodes were hot engine takeoffs on hot Texas days. I still have my download data from 2011 incidents if it will help.

Jim
 
One would think that with both electric and mechanical fuel pumps running, that the engine would be supplied with adequate fuel, even if one pump failed. But that might not be true according to pilot reports that I have heard. The mechanical engine driven pump has a diaphragm that can crack and leak. Not only does the ruptured diaphragm allow fuel to leak out, it also allows air to leak in. A few pilots have reported that their engine stumbled during full power takeoff. I have not heard about a Roax 912 engine completely quitting due to fuel pump failure, only that there was a partial power loss. But in some situations with obstacles ahead, full power is critical.
 
Fuel pump vent line check

Someone on this forum(Roger Lee maybe) suggested putting in clear tubing for a few inches on the upper part of the fuel pump vent line. I did put in a clear section of tubing that I can see through the right forward lower cowl engine opening. As part of my pre flight I shine a flashlight in that opening to see if there is any evidence of fuel or oil in the line. To date I have never seen any thing in the line. Thanks, Bob Kibby
 
Good idea, Bob. I pushed my old style pump to 300 hours before going to the new style. I thought I would be able to see any fuel leakage on the new vent line during preflight, but I'm not so sure. A clear Tygon tube with a loop seal might be the answer.
 
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