New 914 will only run at idle

If you are seeing oil inside the air tube coming from the turbo, then the ball and spring (Check Valve) on your turbo is not seating correctly. This could be the cause of your starting issue. 

Remove the top banjo bolt on your turbo and inspect the ball and spring to make sure it is seating correctly and is clean. You then need to clean out as much of the oil from the cold section and airbox as you can.

See Heavy Maintenance Manual Chapter:

- 78–20–00 TURBOCHARGER (914 SERIES ONLY) 

- 79–00–00 LUBRICATION SYSTEM

 https://www.rotax-owner.com/pdf/MMH_912_914_Ed2.pd

Please see the information in this link - https://www.rotax-owner.com/en/912-914-technical-questions/5086-914-turbo-oil-leak

Please see the information in the attachment.

Haven’t gotten into the turbo oil  system but will check it next. Why would a oil check valve leaking by cause the engine to not run above idle? Could someone explain how it effects the engine running?

After erlier suggestions I also realised an air leak in the induction (between carb & engine) system could also be involved - check integrity of all connections & fittings between carb's and engine. 

Our 914 engine has had the same situation for years. But we learned, how to keep the engine running after using the choke. We use the choke enough, that we can gently raise the rpm and when they don't rise anymore, so that the engine doesn't shut down, we push the choke away very quickly and at the same time we increase the throttle a bit. If you try to push the choke slowly, the engine dies. We haven't bothered to come up with any reason, because this way it works well and the engine runs flawlessly.

I’ve had it for 19 years now and it doesn’t like the transition from choke to throttle being done slowly and will quit every time I try it slowly.. I also have a 912ULS and it’s not so fickle when starting.