Hard starting Rotax 912 ULS

Hi Charles,

It would seem you are in the habit of ground running your engine, when you can't fly  - this is not a good practice.

I have no winter (as you know it) flying experience but I do understand engine management in general and have now about 13 years Rotax 9 experience. 

Due to the engine not being operated within its efficient RPM range and not reaching optimum temperatures for a prolonged period (suggested minimum flight time of 30 minutes) you will have black plugs, condensation/fuel & combustion contamination of oil and may contribute to carbon build up of piston rings/valve seats/stems. Also you are not helping your battery to recharge after, the energy loss in, starting effort.

The use of AvGas is ill-advised, Rotax 9's are designed to run on ULP. The perceived benefits in the use of AvGas are at best suspect (in most circumstances) and will only add to the potential internal contamination of your engine and the faster depletion of your finances. 

No engine "likes" to be just run up periodically or be subject to long pre takeoff /post landing running - you would be better "winterising" the engine for those months that you are unlikely to fly.

I only did that once other than a couple times when I taxied back to my parking spot from the mechanic's shop. And I have since seen that that is not a good idea so I won't be doing it anymore.

So my question now is are the floats OK at 6.6 grams? I have new plugs and fuel filters ready to go. 

Your floats are fine at 6.6 grams

Ok the gremlins seem to have gone. My mechanic finally had time to work on the plane with me(he had chastised me when I told him about my earlier troubleshooting). First he verified that there was spark from both ignition modules. Then he checked to make sure I had properly reseated the carb bowls. I had bought new plugs and gapped them to .025(looks like out of the box they are about .029). We swapped out all the plugs. The only other thing he noticed was that the top plug wires for cylinders 2 and 4 were swapped. So he fixed that. Before all this I had done some online research on the proper starting technique. What I found was throttle out, choke on and when it seems like it's going to fire, choke off and advance the throttle just a tad. I did this and it fired right up. He had me warm it up and then we checked the carb sync. Surprisingly it was all good. I ran it a bit more including up to 5000 RPM(it was chocked and tied down). All good. Too late in the day for a flight but I guess the real test will be when I can go fly it if it starts right up. No real clue what the original problem was.