ROTAX 912 low fuel pressure at take off

Hi Sean, hope the reduction of the ID will deliver better results - pls. keep us updated.

Have you considered to simply close the return line down completely for a test to show that pressure develops the way you want it to? Size zero surely is the smallest jet ever. Trying that may prove the point. And if so it is a matter of fine tuning finding the perfect match for your set up.

As I understand the 912 fuel system the engine should run normally, without a functioning fuel return line BUT I have never actually done this. Even the idea makes me feel uncomfortable.

Which is understandable, Sean. However, it’s worth (and safe) trying. Hundreds of C42s flew about with no return line over years and years until the return line became standard. So did we. After installation there was no obvious change in operation. Whilst we were forced to instal a return line in our C42 at that time we have continued to fly another much more modern high-wing UL which still does not have a return line or need to have one installed up to now.

Rotax has made it a recommendation at some point in the past but by far not all plane manufacturers have followed that up to now. Consequently, the additional risk not having a return line must be rather low.
To actually suffer from true vapor lock issues it requires a mix of conditions and circumstances. If you consider that you’ll probably try without a return line soon. And you can always switch back any time with or without the optimized jet.

I cannot wait to go flying again on the other high wing (with no return line) with pleasure.

Its fairly warm today, 37C in the shade. I think I will wait for cooler weather to try a no fuel return take off.

In the mean time the Rotax 35 looks suspiciously like a Mikuni VM22/210 type slow idle jet.

They come in a range of flow rates 10-140. So fare I have not been able to find out what the flow rates are.

As I understand it, all have the same external dimensions/features;

Anyone care to suggest which Mikuni VM22/210 jet might give me a 3L/hr flow rate?

What no:::---

Hot rodder's???

Fluid dyanamacist's???