hydroguy2

hydroguy2

Well Known Member
I had a beautiful flight this morning, but my friend Neil thought since I have Emag/Pmag I had too much rpm drop. It drops about 100rpm...either side. It's always done that so I didn't think much about it.
Then when I reduced power to idle in the pattern I get a stumble...not the typical RV backfire, but a stumble. A touch of throttle seems to smoooth things out. But always runs a little rough taxiing when hot. It seems to be getting worse. So tonight I went out for a little practice, ran up the lake and back before entering the pattern. Once in the pattern, I pulled power and sure enough stumble. I get a rpm drop and I give it a little throttle to pick things up. 1800 and above seems ok, below that i wasn't certain the thing would even stay running. My stable approach went to **** and did a go around.....Runs great at full throttle. This time aeam the numbers I slowly retard the throttle, and it is stumbling and surging I thought it quit once(but maybe not). Makes for an exciting short final when it seems the engine will quit at any moment. I don't dare another go around, this will be a full stop!. I'm jockeying the throttle to keep it running....btw should I count all my bounces as landings :(
So I taxi back and several other guys notice she is running pretty rough. Once stopped I pull back to idle and the engine surges from 850-1030rpm. I try to lean the mixture, I try full rich, I try boost on & off. Started slowly a couple hrs ago and seems to be getting worse. Weather is warming up around here.

So I'm grounded until I figure this thing out....any ideas?

IO-360 parallel valve, 9to1 comp, AFP injection, Emag/Pmag w/auto plugs
 
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Not sure what you are experiencing there but I suspect the first culprit is plugs.

However, I am relieved when I hear other injected engines run rough at idle when hot. Mine does too but lately I have found the more you lean it out the less rough it is. I think mine will just be a tad rough when hot but for me, learning to lean it out just the way she likes it will make a big difference.

Sorry I couldn't help with your issue. Good luck!
 
Which E Mag?

I just went through something similar. Always stumbled on the ground. Eventually the ElectroAir side failed a runup check.

Turned out to be a bad sensor. Replaced that and it runs smooth.
 
Sounds like an air leak to me

in that it gets worse under high manifold vacuum conditions. Look for a broken intake gasket at the cylinder head (found a small piece missing from one of mine), or other air leaks between the injection servo and the intake port.

Another possibility is foreign material partially plugging an injector or injector line, or even inside the spider. Do all cylinders drop out or just one or two?? Do a bottle flow test.

Doesn't sound like ignition to me. Ignition problems USUALLY show up during high power or high altitude operations in my limited experience.

Good Luck!
 
Busy today and tomorrow, but I'm going to download the Dynon info next. I think it is fuel also. this problem just recently started. Originally It was a minor hesitation when going to idle during a hot engine taxi. then I noticed it more in the pattern 2 flights ago. Last night was 78* and engine temps were up due to some slow flight. But CHT's and EGT's were tracking normally from what I recall. While all my hoses are firesleeved, my UNinsulated red cube is mounted under and between cyl 1 & 3....thinking that may be a problem.
 
Red Cube

I think I recall the instructions state to insulate the cube if FWF. I did this but can't really remember if it's in the instructions or not. I used some giant firesleeve hose about 8 inches long, two slots for the bolts with hose clamps on both sides.
 
I recall that some folks do, others did not. I did not insulate as i wasn't sure I even wanted to leave it there. It is a very tight fit and was already thinking of moving it aft of the FW. this gives me an excuse.
 
UPDATE:

Talked with Don at AirFlow Performance. re set the idle mixture and rpm setting. I was rich. Also insulated the FF redcube and an elbow on the servo. Pulled the plugs, checked the timing.
It ran better but still rumbled a bit during hot taxi. Ran good in the pattern though. I didn't like it still, so started tracing the fuel system for any issues. When I pulled the fuel filter, I found the inlet flare not loose, but not torqued properly.
Anyway got her all back together this morning, running great! no stumbling, bumbling or other scary schtuff. Good thing too as I had a photo shoot in HLN. We were shooting a video for the Big Sky Air Race along with one of the sponsors, RobertAllen Nissan. also did some low pass shots.

We got to close RY34 for about an hour. It was great fun
IMG_20110616_105650.jpg

IMG_20110616_110353.jpg
 
So, what was it?

Was the not-torqued fuel line at the filter allowing air bubbles into the fuel? It is on the suction side of both pumps, but even then, low enough pressure to pull air in?
 
scsmith said:
Was the not-torqued fuel line at the filter allowing air bubbles into the fuel? It is on the suction side of both pumps, but even then, low enough pressure to pull air in?
Click to expand...

maybe....it never leaked fuel, but may have contributed some bubbles to the situation when things warmed up. She ran great all day yesterday
 
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