A couple of flights back with a total of a little over 6 hours on the engine, I had a partial loss of power on takeoff. It occurred at about 300 feet off the deck during a 65 knot climb-out ... the Rotax engine went instantly from 5250 RPM to 4000 a moment after catching a brief whiff of fuel. I pulled the throttle back and then eased it forward slowly ? the engine felt flat so remained at a lower power setting and flew the pattern back for a landing and inspection. The engine was running smooth at the lower RPM. After dumping the Dynon data log and looking for the event, it appeared the left carb went rich. I then used Savvy Analysis to graph the event to interpret the numbers better. The resulting graphs showed that at the time of the abrupt RPM loss, the exhaust temp on the left side went down accompanied by a 0.5 psi loss of fuel pressure to 5.1psi which seems to indicate that the left carb went rich and flooded the left cylinders with too much fuel.
Prior to digging into the carbs, I did verify that a heat gun placed on the left EGT sensor correctly correlated to EMS readings for the left side changing ? it did.
Popped off the left carb bowl and it was clean except for a very very tiny piece of grit in the bottom of the bowl. The floats were floating nicely ? but weighed them just the same and they weighed 3 grams each. Turned on the fuel pump and flushed out the needle valve and verified that the needle valve shut off the flow of fuel ? it did. Also looked to make sure the float bracket was parallel with the body of the carb ?. it was.
Figured gee ? it must have been that little piece of grit that caused the issue. Decided to have a look at the right carb while I?m at it, so removed the right carb bowl and was shocked to find a sizable flake of what looked like black paint in the bottom of the bowl. Then I noticed the float bracket was totally black ? looks like it has been spray painted or has some kind of an oxide coating on it. It appears the black flake I discovered came from the area where the clip for the needle valve attaches onto the float bracket.
I knew things did not look right the moment I saw the float arm, so instantly ordered replacement parts ?. ended up replacing the float arms, needle valves and clips on both carbs so there would be new parts in both carbs. I took photos and sent then to Dean at Lockwood and he said he had never seen a float arm looking like the one in my right carburetor. I?ve attached a few photos for the forum to see ? now mind you, this engine only had 6 hours on it and the float bracket in the left carburetor looked spotless ? it was shiny brass. But the one in the right carburetor is covered with a black substance as can be seen in the following photos. For background the engine was kept in the plastic bag until January 2016 and was installed at that time. Think first fuel in the engine was around May or June 2016 and first start in mid July.
Has anybody seen the likes of the following on a Rotax 912ULS?
The black float bracket was noticeable the moment the bowl was removed.
A new float bracket on the left. One can see where the needle valve clip wore off the black substance ... a flake of it was discovered on the bottom of the bowl.
Looking at the opposite side of both the new and old black float brackets.
Prior to digging into the carbs, I did verify that a heat gun placed on the left EGT sensor correctly correlated to EMS readings for the left side changing ? it did.
Popped off the left carb bowl and it was clean except for a very very tiny piece of grit in the bottom of the bowl. The floats were floating nicely ? but weighed them just the same and they weighed 3 grams each. Turned on the fuel pump and flushed out the needle valve and verified that the needle valve shut off the flow of fuel ? it did. Also looked to make sure the float bracket was parallel with the body of the carb ?. it was.
Figured gee ? it must have been that little piece of grit that caused the issue. Decided to have a look at the right carb while I?m at it, so removed the right carb bowl and was shocked to find a sizable flake of what looked like black paint in the bottom of the bowl. Then I noticed the float bracket was totally black ? looks like it has been spray painted or has some kind of an oxide coating on it. It appears the black flake I discovered came from the area where the clip for the needle valve attaches onto the float bracket.
I knew things did not look right the moment I saw the float arm, so instantly ordered replacement parts ?. ended up replacing the float arms, needle valves and clips on both carbs so there would be new parts in both carbs. I took photos and sent then to Dean at Lockwood and he said he had never seen a float arm looking like the one in my right carburetor. I?ve attached a few photos for the forum to see ? now mind you, this engine only had 6 hours on it and the float bracket in the left carburetor looked spotless ? it was shiny brass. But the one in the right carburetor is covered with a black substance as can be seen in the following photos. For background the engine was kept in the plastic bag until January 2016 and was installed at that time. Think first fuel in the engine was around May or June 2016 and first start in mid July.
Has anybody seen the likes of the following on a Rotax 912ULS?
The black float bracket was noticeable the moment the bowl was removed.
A new float bracket on the left. One can see where the needle valve clip wore off the black substance ... a flake of it was discovered on the bottom of the bowl.
Looking at the opposite side of both the new and old black float brackets.
