Getting engine to run again

"I have it started a few days ago for a short while, but shut it down within a few minutes because of some problems I see. This is my first experience with Rotax 912 engine, so I would appreciate all your suggestions.

"1. The engine would start, but would not hold good idle.

Basically, it started with choke. But RPM would flucturate between 2200 and 1900. It would almost die at 1900, then climb up to 2200, then drop back to 1900 and cough, and eventually die."

Rotax have a very specific start procedure - find it in the Operator Manual. 

First - Ensure the battery is in good condition - if in doubt replace. A weak battery will only crank the engine slowly, and cause damage to the starting mechanism (Sprag Clutch & starter motor).

First again - Ensure that your carburettors have been correctly statically balanced/set up.

Another First - Fresh fuel. The volatile fractions, that assist with engine start, are amongst those reduced/lost in old fuel. 

The Basics- Prime fuel system, using Boost pump, until fuel pressure stabilises. Turn off pump. Close throttle completely. Open Choke completely  Crank engine. Start should be close to instantaneous. Close choke, almost immediately and at the same time use throttle to maintain between 2000 - 2500 rpm. Allow engine oil to warm, minimum 50C. before higher rpm/loading engine.

Note: Engines fitted with Soft Start systems will have an automatic engine rpm increase to the loww 2000 as part of their operation. The above procedure should still be followed.

"2. The one I worry most is that the oil pressure is very low, especially when it is about to die"

I did some research now and found that I will need to prime the oil system after an extended oil change. I acutally took the oil tank out entirely to clean up the sludge in the bottom, so this is probably something I missed. "

It strikes me that you have not read the Rotax Operators Manual for your engine (free download on this Forum, top of opening page)

"I have ordered one of these oil prime kit". 

What oil prime kits?

Rotax 9's oil system are usually purged using low compressed air & hand cranking of prop - read the manual

Thanks for the info. I will get to the manual.

The prime kits: I found one on Aircraft Spruce. It is on back order now, but I put in an order and hope it is something that could solve the problem for me. You are right, I need to go through the manual first.

Thanks a lot.