Rubber gasket Carb. housing

@Finn:  Please fill out a CSIR report on this issue.

See this link for instructions https://www.rotax-owner.com/en/support-topmenu/csir-service-information-report

We run mostly all 91 oct. with ethanol here in Arizona and to my knowledge haven't heard or seen this. When I do annuals I always pull bowls off and haven't seen this. It would be interesting to see this out. You could drop a gasket into a jar of 91 oct. with ethanol.  I have to go to the field in the morning. maybe if I can remember I'll do that.

Finn.

I had a similar issue with swollen rubber a few months back. It might be also worth checking your diaphragms.

I was using cork gaskets so did not show there. 

It was ethanol free fuel.

Here in New Zealand a fuel company started selling 100 octane mogas. It looked like it was going to be a fuel from heaven for Rotaxes, No lead issues &  would keep its octane level for 6 & maybe out to 12 months.

Before using it I contacted them to see if any issues with rubber components (I operate over very hostile terrain.)

I was told they had not seen any. It could however discolour certain plastics if they were then exposed to UV. That did not really concern me as my tank fibreglass.

After 40 hrs of running on  it the engine seemed to be performing as before however when removing the diaphragm caps to replace the carb needle circlips they jumped out like a Jack in the box. Very swollen. (See pics) It was 36 hrs since last flown.

After sitting on the bench for 12 hrs they returned to normal size. 

I contacted them again and their thoughts were it was not the fuel causing it. I then did an immersion test asRoger mentions above. Yes it was the fuel. Probably some stabilisers they had added.

After new diaphragms & O rings now flown 200 hrs and all good.

Wrote an article in our aviation mag warning others.

Pete Avery

I over cropped the pic above.

here again.

Also forgot to mention changed diaphragms, O rings and went back to running on 95.