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Building Integrity
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Date:  11-16-2015
Number of Hours:  3.00
Manual Reference:  Section 2
Brief Description:  Mystery Solved...finally

So the mystery problem with my engine's hesitation and stuttering has finally been solved and it's something that every UL Power needs to be aware of.
When I got my parts back from UL Power, they claimed they were able to fix the stuttering from idle to 1300rpm or so and they did. It throttles up much better due to a leaner mixture. However, as stated yesterday, the midrange and WOT performance was much worse. How could this be? Today I removed the spark plugs for cleaning and found the culprit. Remember how well my cooling plenums work? Like TOO WELL! Like the Hottest cylinder is 280 on a HOT day....ya. So having an engine that I cannot lean out, a major problem was brewing. Many pilots will lean the mixture of their engines while taxiing to keep the plugs from fouling, however, UL Power doesn't agree with this. In Fact, they make it excessively rich at idle in order to keep the temps down. This is TERRIBLE and most pilots know it. Not to mention, my taxi temps are really low as well. SO, if you have a really cool running engine that never heats up, then carbon will build up and the plugs will constantly foul. Bingo. 10 of my 12 plugs were completely fouled. I had the airport maintence shop clean them up and I now have a completely different engine. As I ran the engine up to WOT the static RPM came back, and after letting the temps come up into the green, the hesitation was almost completely gone!!!!!!! I am confident that if I raise my CHT's the eventually the carbon will burn off and I will have a fantastic running engine. So lesson learned here, Keep your engine running Hot. This of course means lower drag for me, and a faster airplane :)
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thick carbon deposits on pistons

thick carbon deposits on pistons

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Plugs are fouled

Plugs are fouled

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Cleaned up and ready to run

Cleaned up and ready to run

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