snopercod
Well Known Member
Something went amiss two days go on a 1 hr. cross country flight at 7,500' and I'm searching for ideas. Perhaps someone here can point me in the right direction. My normal routine when reaching cruise is to pull out the mixture control maybe 1", let things stabilize for a couple minutes as the speed builds up, then start the leaning process with my JPI EDM-700. I usually lean to peak and leave it there unless the engine is running rough. In that case, I enrichen 50 degrees. My four bar EGT display usually isn't quite level, so I adjust the throttle a tiny bit until all four EGTs are a straight line on display. The throttle butterfly works magic to even up my fuel distribution.
So on this flight, EGT 1 (red line) was way low (230F), and EGT 2 (green line) was also low (150F). No matter how I fiddled with the mixture and the throttle, I couldn't get that nice straight line. The engine wasn't running rough, but I could feel an unusual vibration. My airspeed was normal, so I kept on to my destination. (My runup had been completely normal with equal mag drop on both mags.)
The return trip was the same. I really didn't realized how messed up the EGT/CHTs were until I got home and dumped the data. The #1 CHT was way low as well. (#1 is red, #2 is green) Just look at this mess:
My first thought was spark plugs (which really wasn't right), so the next day I pulled the #1 plugs. The top plug was sooty, the bottom plug was a nice tan color. The resistance checked good on both plugs (after I used emery cloth on the electrode to get a good connection).
Then I panicked, thinking that if both #1 and #2 were messed up, that it had to be the common intake lobe for #1 and #2 going bad on me. This possibility is always in the back of my mind since my engine sat for several years during my build. My engine analyses have always been good, but today I removed the oil filter, cut it open, and removed the pleats. I held them open as my lovely wife poured MEK over them into a coffee filter. (The MEK ruined her nail polish, but she forgives me.) Thankfully, there was no significant debris found, and almost nothing magnetic.
So tomorrow I'm going to change both plugs "just because", even though a fouled plug should have made the EGT go UP, not DOWN, I believe. After warming up the engine, I'll do a compression check.
I also intend to remove the carburetor and make sure my 2-piece venturi is still intact, and that nothing else is wrong in there. I recently installed a carb temperature gauge, so I need to insure the probe (on the cyl 1 and 2 side) is still intact.
Other than that, the only thing I can think of to check are the plug wires to #1, but that wouldn't account for the low EGT on #2. Maybe something in the mag?
I'm down to grasping at straws here, so any SWAGs would be greatly appreciated.
P.S. I do have a traditional primer going to cylinder #1, but thought I had that fixed. If push comes to shove I could cap it off as a test.
So on this flight, EGT 1 (red line) was way low (230F), and EGT 2 (green line) was also low (150F). No matter how I fiddled with the mixture and the throttle, I couldn't get that nice straight line. The engine wasn't running rough, but I could feel an unusual vibration. My airspeed was normal, so I kept on to my destination. (My runup had been completely normal with equal mag drop on both mags.)
The return trip was the same. I really didn't realized how messed up the EGT/CHTs were until I got home and dumped the data. The #1 CHT was way low as well. (#1 is red, #2 is green) Just look at this mess:
My first thought was spark plugs (which really wasn't right), so the next day I pulled the #1 plugs. The top plug was sooty, the bottom plug was a nice tan color. The resistance checked good on both plugs (after I used emery cloth on the electrode to get a good connection).
Then I panicked, thinking that if both #1 and #2 were messed up, that it had to be the common intake lobe for #1 and #2 going bad on me. This possibility is always in the back of my mind since my engine sat for several years during my build. My engine analyses have always been good, but today I removed the oil filter, cut it open, and removed the pleats. I held them open as my lovely wife poured MEK over them into a coffee filter. (The MEK ruined her nail polish, but she forgives me.) Thankfully, there was no significant debris found, and almost nothing magnetic.
So tomorrow I'm going to change both plugs "just because", even though a fouled plug should have made the EGT go UP, not DOWN, I believe. After warming up the engine, I'll do a compression check.
I also intend to remove the carburetor and make sure my 2-piece venturi is still intact, and that nothing else is wrong in there. I recently installed a carb temperature gauge, so I need to insure the probe (on the cyl 1 and 2 side) is still intact.
Other than that, the only thing I can think of to check are the plug wires to #1, but that wouldn't account for the low EGT on #2. Maybe something in the mag?
I'm down to grasping at straws here, so any SWAGs would be greatly appreciated.
P.S. I do have a traditional primer going to cylinder #1, but thought I had that fixed. If push comes to shove I could cap it off as a test.