fbpx

 

Hi all

Am a new Rotax owner (Feb 18) so still feeling my way around what to expect, whats reasonable / not reasonable etc when it comes to rotax engines etc.

Find myself in a situation where I would very much appreciate advice from more experienced, expert rotax owners.

Have had not one, two, three or four but five replacement windscreens fitted over a one month period. Cracking has been established as caused by fuel from leaking carburetors spraying over the windscreen during flight.

We are remote too, so getting mechanic up to replace a windscreen is around $3000 each time.

Engine had done no more than 350 hours since brand new (Feb 18). The aircraft agent's LAME identified the problem as sunken float on the left hand carbie.

Looking through these forums, there appears to be consistent problems with the Rotax carbies leaking fuel.

The question I would love your points of view on is whether its reasonable for a brand new plane's carbies to start leaking at 350 hours. Just feeling like the carbies on the engine are faulty if this can happen this quickly?

Thoughts please.

And also my sincere thanks for the quality and quantity of advice on this forum - blown away by having this much knowledge to hand.


Aussie Matt
  • Re: Rotax carbie problems

    by » 6 years ago


    What kind of aircraft is it and could you put out some pictures of the engine? Are the carbs balanced? Vent tubes properly installed? Propellor balanced and each blade pitched equally?

  • Re: Rotax carbie problems

    by » 6 years ago


    Howdy Matt,

    Bing had the float problem for a while where they would absorb some fuel and get heavy and sink. That should all be fixed. Floats are now supposed to be weighed at each annual and max weight is 7 grams as a pair. What I normally see when I weigh floats is anywhere from 6.0 - 6.4 grams. I would think a new aircraft with a Feb. 2018 build or at least close to it would have newer floats and certainly if you have replaced them. The older floats can be detected by looking at the holes that go through the float body and on both ends you see a brass flare of metal. The new floats have this brass recessed down inside so it does not come all the way out to the top and flare on the edges.I would be surprised if fuel would cause a windscreen to keep cracking. That is usually caused by screw holes that hold some windscreens being too tightly drilled and then vibration cracks the plastic. I had a helicopter that specifically said to make sure the holes were the next hole size larger to allow for movement, expansion and contraction.

    As far as carb leaks there can be more than one cause. It could be a heavy float, but the fuel should go out the vent tube. You could have a bad carb bowl gasket and the fuel should drop down into a drip try / heat shield. Vibration from the engine can cause the plane to shake enough that the floats can not control the fuel level in the bowls and it again will come out the vent tube. Causes of common vibrations are poor carb sync, bad gearbox, bad prop balance and or blades not pitched equally, bad engine mounts and big mag drop differences caused by an electrical issue.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


    Thank you said by: Matthew Winter

  • Re: Rotax carbie problems

    by » 6 years ago


    Your windshield cracking or crazing could be associated with ethanol-laced automotive fuel interacting with cut edges on Lexan plastic. This is a common problem on RV-12 Lexan rear windows. Van's Aircraft's suggested solution is to use a protective manufacturer's coating on the Lexan's outer surfaces and to seal all hole cut edges and perimeter edges with an appropriate sealant (e.g., fuel tank sealant) -- this has worked well for me. The newer RV-12 plexiglass rear windows are apparently not affected by the ethanol fuel component.

    As Roger noted above, be sure that all of your windshield mounting holes are generously oversized to permit for differential movement (e.g., thermal expansion and contraction) of the plastic windshield.

    Thank you said by: Matthew Winter

You do not have permissions to reply to this topic.