Hello and your advice please

[Watfox]

Hi

I'm in the UK and have been flying a Mk4-1200 with 912 Rotax for about a year now. Love the a/c, hate my lack of skill, but will hopefully get there in the end. Your experience may answer this, you have far more over there than we do here.

I have the twin cable throttle system and it has no stop when pulled back to idle. Because of balancing problems we fitted springs to the carb arms (so that in event of cable failure it goes to max power) This appeared to help and I have adjusted to this system. However idling on approach is now a fun exercise trying to judge where to stop pulling against the arms.

Has your Rotax experience come up with any set up where there is a physical stop on the throttle sytem?

Hope this makes sense

Gary

[Av8r3400]

There should be idle stop screws on the carbs to set how low you can pull the throttle back to.

Is yours the vernier or friction-lock style throttle?

[Watfox]

Thanks for the quick reply!

I have the metal friction lock twin cable style throttle. It was supplied by John and Debra just over a year ago. I believe it is the latest version.

On our Rotax set ups in other a/c we usually have a physical stop at the pilot end, then work the balancing from there. However we just couldn't get the two cables to move together all the time. Looked like the cable needed to be thicker so it couldn't arch as it left the cable housing at the carb end. We kept on flooding one carb.

So we added the springs to give some pull on the cable. This pulls them together

We idle at 1800 nicely now, but without that phsyical stop at the throttle handle end you can pull too much and bend the carb arms. I have to feel that carb shut and double check the rpm to confirm I'm not going to drop too low.

Gary

[akarmy]

Here's a picture of the carb. The screw with the red locktight on it is the idle stop adjustment. By turning it you should be able to set the idle speed with a hard stop on the carbs. However as you indicated that will not stop you from pulling hard on the cables and bending the arm.

[Watfox]

Thanks Andy, looks like you have the same set up.

I think I am going to have to try and balance them w/o using the spring set up, that will allow the natural stop to be used .

Over here the Rotax people don't like the set up we have and advise the use of springs.

Think I'll go American

Thanks

Gary

[Av8r3400]

On my plane(s) there is a spring on each carb that pulls the throttle open.

The cables pull against these springs to close the throttles, just as you have now. Some folks have used offsetting springs to overcome *some* of the opening force, but I've never seen these "opening springs" removed completely.

[akarmy]

Actually I removed my opening springs completely. I played with the carb setup quite a bit and never could get the right amount of spring tension vs friction on the throttle. It would spring to life without warning when taxiing etc. I finally just removed the springs all together and it works just fine. I didn't have any issues getting the carbs synced without the springs.

I know there is a risk that if a cable breaks it won't go to full throttle (neither will most lycoming installs) but that's weighed against the risk of uncomanded throttle movement due to spring tension.