How bad is it to run on just 3 cylinders?

I suggest you refer to the Operator's Manual ...

Thank you but I didn't see anything in there relating to this.

If what Glenn Martin said is correct then I will not try to test this because that amount of vibration would be terrible for the engine. If it is that strong much more than "rough running" then I'm sure there is no danger of me mistaking that kind of vibration for any other source.

If you think about it, it will be just about the same a throwing a rod and running on three cylinders.

It will warrant an immediate engiine shutdown before the engine shakes off the mount followed by a precautionary landing wherever you might be.

It is something you will never want to experience and something you will Not be able to ignore.

Thank you! I did not know how serious that was. It seems like one cylinder failing is just about as bad as a total engine failure.

Competitor engine manufacturers sometimes advertise that it is ok not to have redundant fuel injectors because the engine can still run on 3 cylinders but now it makes lots of sense why Rotax would have so much redundancy even for each cylinder because loss of one is pretty disastrous.