912 ULS with "hiccup" (mis fire)

Hi Coen,

"The vent line are routed "from factury" into the air filters"  This statement sounds to be contrary to Rotax instructions.

 The main function of the "vent lines"/tube is to keep the air pressure within the carburettor float bowl the same as the inlet air to the carburettor. By having the tube inside the air filter you may be lowering the air pressure in the float bowl. This is even more likely if the air filter is in poor condition or has become contaminated in use.

Hello

I have a follow-up om our problem.
The aircraft continued to suffer from "hiccups" and it became more frequent....

We cloud not find any problem with the fuel supply, so in the end we replaced the carburetors by revised ones.
The engine runs fine now, no more hiccups.

The original carburetors were completely disassembled, and much to our surprise, the membranes were swollen, even to the point that they were no longer fitting in the carbs. (see picture in the attachment).
This will, in some way, have caused hiccups.
The carbs are going to be completely revised, with new membranes.

Well there's still the question: that caused the membranes swell?
It is not normal

And I have to make a correction on my input about the float bowl vent lines: hey are not routed into the airfilter (as I mentioned before) but they are routed into the airfilterbox, just next of the airfilter.
And indeed, the positioning of these lines have a lot of influence on the running of the engine (more then I expected).

Thanks you for your suggestions to solve the problem.

Best regards,

Coen Jansen