Use of 100LL

The 912Is runs leaner and therefore uses less fuel which in theory should be better.....However RFI engines to run well rely on more sensors than the older carbed ones. These sensors can be effected by lead deposits.

Lead creates ugly looking deposits everywhere, valves, clutch, cylinder heads etc...so not a good idea, I have seen a 1000hr 912ULS run exclusively on 100LL stripped down looked terrible....But it was still running OK soooo....

Using 100LL in either engine occasionally as you imply is not a problem. I am sure you drive to the Airfield ? just stop at the nearest Servo on the way as many do with a few 20l red Jerrycans in your boot, Problem solved, and IF you have a high wing then gym time done too..

Many people use an additive when they have to use 100LL which I am sure helps.

Summary....Unless you are using 100LL more that 25% of the time then no issues with either engine

Ok thanks for that.  Does the use of car fuel (what type do you use?) create problems if it is sitting around in the tanks between flights?  Does it go off?

Hi Adam,

Rotax engines are DESIGNED to use Auto fuels so that is the best for them they can use 100LL but not best.

So long as you do not leave the Auto fuel for more than a year you should be fine, also use Auto fuels with no ethanol.

I have never heard or seen an issue with old auto fuel and we have over 100 Rotax powered aircraft on our field. Occasionally someone whom has left it for a year or so decides to drain the fuel out and put in their car and put fresh fuel in the plane...probably a good idea

Rotax has a document on the right fuels to use, but simply here in NZ and I assume Aus is the same we use "premium" RON 95 in the 100 hp engines and 91 in the 80 HP

Thanks again - good to hear about the reliability of 95 car fuel.  In any case, by the time I finish my build the new G100UL will probably be widely available in Australia.

G100UL would need to be approved by Rotax first. Check the Service Instruction on approved fuels, I cannot see that there but maybe it will be in the future.

Rotax engine users have used the fuel that the engine was designed for (Mogas) for 38 years...without problems....personally I would not like to change that for no good reason...

But in the end it is your plane you can experiment..thats one of the great things about these classes of aircraft !