912 missing carb?

[mcomeaux53]

Having a mystery with running.
No problem with run-up and takeoff.
After approx 30-40 minutes into flight feels like vibration/miss.
Pull throttle back to 3500-4000 rpm for brief moment then advance to 5200
And it returns to smooth operation for short period then again stumbles.
Any ideas? New plane and not much experience with the 912.
Motor has 360 hrs

Mike

[avidflyer]

my first thought is you are burning more gas than it's getting... Just a guess and first thought though so take it with a grain of salt. Also, it's 11:30 PM Jim Chuk

[kmach]

Any work done before the problem ?

I think the carbs should be checked for debris contamination in the float bowl, proper float level, cleaned and ....

after , synchronize the carbs well .

Check the whole fuel system from tanks to carbs, partially blocked filter somewhere? fuel line "flap" ?

Do you have a fuel pressure gauge , if so what is it showing ?

If you have a backup electric fuel pump , does turning it on help ?

Just some things that come to mind

[mcomeaux53]

I just purchased this aircraft recently. We synced the carbs today and I will
Fly tomorrow and see if any changes. Just weird how it runs so smoothly first 30-40 minutes before she acts up. I'll post my results as I work through it.
Thanks for the input. Great site here.

Mike C.

[Danzer1]

Mike,

Have you considered doing further testing static?

Syncing the carbs likely will not produce a positive result unless they were way way off.

Have you inspected the plugs - this is where you can tell what your fuel delivery condition is. White, sooty, dry, wet, black and on which plugs and where on the plug. It's the 1st thing I'd do before flying it!

Do you know what the CHT's and EGT's and RPM were just prior to the problem and what they were after the problem develops?

A rich condition can take some time to show as the engine heats up. I suspect that might be the case here.

Greg

[Eric]

Hello

Maybe a problem into the ignitionsystem? failing sensor / coil or something

[Rowdy1]

I am also new to the 912. I bought a kitfox 3 about two years ago and had a roughness in the mid range. I checked syn mechanically and it is good. I found an article on the importance of the carb vent tubes being 120mm and routed between the carb bowl and the retainer spring. This significantly helped it above 2800rpm. Then I sitll had a roughness between 1900-2600rpm. I checked the idle mixture screws and they were 1 1/2 turns out. I adjusted the idle mixture and it smoothed out the rest of the range. Vacuum syn is the best but the vent tube and the idle mixture adjustment made a huge difference. Hope this helps.

[Paul Z]

I concur with Mike join the Rotax web site a lot of good maintenance and installation how to videos.