In April sent gearbox and carburetors to Lockwood for inspection and five year inspection of carbs. Gearbox ok, put carbs back on and engine would miss violently, sent carbs back to Lockwood and they ran perfectly on their test engine . Put carbs back on and still misfired, but not as bad as befor. We have trimmed the plug wires and reset the plug caps, changed the spark plugs, ran on new and old ones, compression on cylinders good, switched out ignition boxes to a known good set. Synced carbs with a carb mate and vacuum gauges. Checked for stuck valve or soft lifter. Most of this work was done by A Certfied Rotax mechanic. Engine ran fine befor the annual inspection. Engine runs smooth on the soft start modules and starts to miss after engine kicks off the soft start. Engine does start right up as it always has. Maybe next check would be the pick ups on the back of the engine??? Suggestion’s? 912uls engine 700 hours.
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Misfiring engine
- Thread starter lewy
- Start date
sounds familiar
my 912 ULS was hard to start, rough running & "mag" check was way out of bounds. I similarly performed most of your stated troubleshooting but was at a loss to a solution. Drained & replaced fuel, has been purring ever since. Just saying, one man's story.
my 912 ULS was hard to start, rough running & "mag" check was way out of bounds. I similarly performed most of your stated troubleshooting but was at a loss to a solution. Drained & replaced fuel, has been purring ever since. Just saying, one man's story.
Not a Rotax, but…
I’m no Rotax expert by any means, but maybe there’s an intake leak? I don’t even know if that’s feasible for a Rotax (I’ve never even seen one uncowled), but an A&P and I were just chatting and he told me he ran into an engine with an intake leak that caused 1 cylinder to anneal the valve springs because it got hot. Ran fine at idle and when first starting, but had problems once things got warm or ran fast (I don’t remember). Again, I’m no Rotax expert, just trying to help. Good luck.
I’m no Rotax expert by any means, but maybe there’s an intake leak? I don’t even know if that’s feasible for a Rotax (I’ve never even seen one uncowled), but an A&P and I were just chatting and he told me he ran into an engine with an intake leak that caused 1 cylinder to anneal the valve springs because it got hot. Ran fine at idle and when first starting, but had problems once things got warm or ran fast (I don’t remember). Again, I’m no Rotax expert, just trying to help. Good luck.
RFSchaller
Well Known Member
How about the plug wire connections? Might be intermittent. Of course there are the ignition coils, but unless it’s a primary circuit connector it seems the coil would self destruct if the coil insulation was damaged.
If the carbs were sent to a specialized shop twice and tested perfectly, I would probably not suspect the carbs themselves. I would be looking at HOW I installed those carbs. It sounds like this was part of a CI and if so, I would back step over everything I put my hands on during the CI. The fact that installation 1 was bad and installation 2 was better, leads me to believe that you are creating issues with the installation or the attachment of something to it. The fact that the soft start works perfectly and once past that runs poorly, would have me thinking "what is different between those modes?" The answer should point you in a good direction. Have never even seen a Rotax, so can't offer much beyond this.
Larry
Larry
WJaviation
Active Member
Drain fuel. Drain carb bowls. Fresh fuel and reattempt.
Was there a resolution for this issue that can be shared??
KALEWIS
Well Known Member
Oh yes - and it was a simple fix, but somewhat embarrassing!
Long story short - one prop blade was set correctly, and the other, well, let's just say was not. A keen eye from a visiting mechanic helped resolve the issue in about 10 minutes.
Thanks, and appreciate your candor. No need to feel embarrassed and extra eyes are always warranted. Glad to hear it was an easy fix.
Piper J3
Well Known Member
This seems a little sketchy.... Advise if problem remains fixed after a few flights.
As has been discussed here many times, even a slight mismatch in blade pitch will cause a detectable roughness.
A more severe mismatch could easily cause a roughness ad enough that it would feel like the engine was running rough.
KALEWIS
Well Known Member
Sketchy????
Pitched the prop, properly, and all is well.... since then have about 35 hours and all is fine.
