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barry(at)pgtc.com
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 Posted: Mon Jun 25, 2007 6:34 am Post subject: No Title |
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Engine Running Rough
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In January, 2007 my Kitfox IV with a 912 S engine threw all three blades of my GSC propeller. There was one big “bump,” the engine stopped and I landed without incidence. Observation of the engine revealed that both carburetors came off and the engine mount was damaged. I sent the gearbox to Lockwood and performed a runout test on the crankshaft with no damage either indicated. After installing a new propeller and engine mount, the engine ran fine for about 12 hours of local flights.
Then, Saturday before last, June 16, during a Young Eagles rally, the engine started running rough. It would idle smooth but became very rough at about 3000 rpm. I suspected a kinked fuel line, removed the fire shield, saw nothing, and replaced it. Then it ran smooth and I flew it a few times with no problem. The next day I flew it about an hour with no problem. Last Friday, June 22, I started it and it was rough again at about 3000 rpm – I mean really rough and would not run at a higher rpm. In both of these situations the right carburetor was considerably cooler than the left.
At this point, I thought it appropriate to run a compression check but when I removed the first spark plug I saw it was heavily coated with soot. I removed all the plugs and they all were the same way. Then I opened both carburetors, top and bottom, but could see nothing that would cause the mixture to be rich. These plugs only had about 25 hours on them. I installed a set of old but clean plugs and put the carburetors back together, started the engine and this time it went to about 4000 rpm before cutting out and running rough. Now the carburetors are both about the same temperature. I removed the top plugs and the ones on the left side were clean and the ones on the right side were covered with soot.
What to do? I tend to believe the shock of losing the propeller blades caused some kind of problem with the carburetors.
Barry West
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skyring
Joined: 01 Nov 2006
Posts: 32
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| Posted: Tue Jun 26, 2007 8:43 am Post subject: Re: No Title |
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Barry I offer this information with reservation because I am not a Rotax expert. Like you I would be linking the problem to the trauma the engine underwent with the blades departing but the symptoms you describe sound like the problem we were experiencing for months and have only recently solved.
The Rotax 912ULS would run up to about 70% power and then start to run rough and not go any further. This was completely intermittent and unpredictable. Some times full power some times not. It was a new motor.
In the end a strip down of the carburettors and a very close inspection found three tiny pieces of metal, possibly pieces of thread, in the sub chamber under the needle at the bottom of the main float chamber. I'm describing this from someone elses description because I didn't see it myself. Apparently, occasionally one of these tiny bits would get under the needle. The Rotax now runs fine and we are getting on with the testing.
I stess this is just our experience and may have nothing to do with your problem but the symptoms you describe sound similar to ours.
Kerry.
Kitfox builders helper. S5 Outback 912 ULS.
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