New 914 will only run at idle

David, 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.

Worked on the 914 yesterday. Checked the ball and spring check valve at the top of the turbo and it was clean. The engine will start and stay running if the choke is turned off quickly and throttle advanced quickly at the same time. Got the carb balance done and it smoothed out some but still seems to run a little rough at lower RPM. A question for those that have had a 914 for awhile and have learned to live with the different start procedure compared to a 912 or normal choke start gasoline engine have you been able to figure out why its harder to start? Does anyone have a 914 that starts and runs fine with letting the choke off slow and advancing the throttle slow?

A close friend has a 914 Bristell that starts (cold) easily and requires no special procedure or practice. The throttle can be advanced with the choke full, half or off.  We usually leave the choke on for 30 seconds to 1 minute then go to half choke for another minute.  The throttle can be adjusted easily throughout the warm up period.  

I know you said the plugs were black from running rich, but that could be from having to leave the choke on.  I have seen this behavior more often in motorcycle engines and it’s almost always a problem with the carburetor idle circuit. If fuel has set in the bowls and partially clogged the Idle jet the engine will behave like this.  When the choke is on, the idle circuit is rich enough to run, but when the choke is removed the idle circuit can’t supply enough fuel through the partially clogged idle jet. So, you are forced to quickly advance the throttle enough to move past the idle circuit and into the midrange circuit where the fuel is regulated by the main jet and jet needle. The engine should not exhibit the behavior you are experiencing.  

My experience is the same as yours Ronald.

Our problem of the “new 914 Turbo will only run at idle - with choke ON” has been resolved. 

The solution was to thoroughly clean the carburetor internals, especially with clean  carburetor idle jets / ports on both sides.  

Carb cleaner eliminated the gum and varnish from inside the carburetor - idle jets and ports,  apparently caused by stale MoGas fuel and a several month time period of NOT running the new  914 Turbo engine while the new 914 Turbo engine, fuel lines, wiring, sensors, P leads, …, more…,  were being transferred from a ground engine test stand over to the actual airplane’s  firewall ring mount.

ALL engine RPM throttle settings are now smooth and normal - as expected,  from idle at about 1850 RPM to full throttle past 5600 RPM.

With clean carburetor jets / idle ports, the 914 Turbo engine starts easily - just like the old Rotax 912 engine did - no special choke operations or quick burst of throttle input, and the 914 Turbo engine runs as it should !

Dave and Ron