Hey Dave,
I have a JJ1800 which I purchased not too long before Christmas, It's essentially used as a testbed work horse. I've been running it for quite some time using different fuel and oil combinations trying to find a happy medium, I've found that these engines will run on just about anything that will burn, that being said, the best combination I've found seems to be the good old Jet-A1 with 4-5% Mobil Jet 2, this creates less of a carbon build-up than using other fuels such as diesel and synthetic 2-stroke oils.

My engine has just a tad over 27 hours on it so far, (1622 mins), my HDT indicates 173 cycles, that's an average of ~9.4mins per cycle, all this on the same set of bearings too. The bearings are due to be replaced very soon though as they are getting a bit tired. I have run it for up to 25 mins at a time at various rpm settings with no ill effects other than disturbing the neighbors with the noise!!

My engine doesn't see any runways since it's not mounted in a model aircraft so the ingestion of dirt and dust is minimal compared to most of you, I suspect this is why the bearings have lasted well. It's basically just a testbed for my afterburner system and will eventually see service in a 1/5 scale jet dragster.

Cheers,
Smithy.