One engine using too much fuel

Disclaimers: No nothing about 912 is engines or the application of two (twin) Rotax engines.

I am not surprised that two engine's, in the same application, have slightly diffrent fuel consumptions.

Lots of potential for small  differences = diffrent fuel consumption

Manufacturing tolerances  eg in compression = differences in combustion efficiency = differences in fuel consumption.

Same for carburettor etc etc.

Propeller differences due to minute variations in prop finish, pitch settings.

Air flow variations, due to wing or even propeller as not counter rotating.

Given they were matched I would suspect a change in throttle position.  Check they are both exactly the same TPS sensor readings.  If one engine is into ECO mode and the other not it would account for a big difference.  Depending on your instruments you should be able to see this.  

Cheers

Very good point RW

Completely forgot about the way Rotax connect their throttle cable (could be hard to synchronise two throttles/engines & may slip) - we humans so often zero in on the complex, high cost solution.

Yes, the post is actually on an iS engine with the throttle body having a throttle position sensor on each engine, TPS.  must be an Aircam i guess.  Anyway the injected engines have a rich condition when running at take off and below about 97% on the TPS they go into ECO mode for fuel saving.  

My guess with so little information is that one engine throttle is no longer balanced with the other, it could cause a huge difference in fuel flow.

Cheers

Thanks of the reply. I'm somewhat new to Rotax so I might not understand what you're saying, but the engines are running at exactly the same RPMs. In this case about 4,400. But you bring up a really good point. One of the engines is in ECO mode the other (burning more fuel) isn't. This probably accounts for the difference in fuel burn.

Having said that, I have no idea what has changed. The engine that isn't in ECO mode is hardly putting out any power and should be in ECO mode. For the first 70 hours they are both in ECO mode at these RPMs.

My new question is, why doesn't the engine go into ECO mode?