Hi,

I built Hangar 9 Cub and I installed Evolution 10cc (Gas engine).

So far I did maybe 10 flights and everything went well until my last 3 flight.

I notice, when I was on the final, once I reduced the throttle almost all the way down, the RPM go down and after few seconds the RPM start to increase without me touching the throttle stick?

When the airplane was on the ground I did engine run up and it seems like the phenomena repeating itself. (only when I take Throttle all teh way down)

Anyone have any idea what’s the problem? (is it engine tuning or servo problem? or other)

Please advise.

Regards
Meir

Well, to find out if it is a servo problem, try to re-create the problem while you watch either the throttle servo itself, or at least watch the throttle linkage to see if it is moving.

AV8TOR

but even if its moving, what move it? is it the engine or the servo? how can i tell?

If the servo is moving, and you aren't telling it to, it's time to replace it.

well, the servo are new (HITEC), but i agree, even if it's new it may by the reason..

Would the engine require some tuning as it breaks in and have you checked for air leaks . Seems that some are having issues with the supplied fuel filter . Good luck and swapping out the throt. servo would be pretty easy . Cheers the pope

You can also try adjusting the low throttle end-point.

Check your transmitter throttle stick. I have had problems where the stick did not return to the same place every time, especially if it has a ratchet detent. Good luck, red

i checked the stick and it looks fine (i'm using DX9).
I will check later if i have air leaks and update.
I will also going to try adjusting the low throttle end-point - do i need to open or close it?

Thanks for your help guys
Meir

With a DX9 you can check the servo monitor screen to be sure there isn't a problem with the throttle stick potentiometer.
If there is a throttle idle stop screw still in the engine it should be removed. The idle stop screw is only for non RC applications.
Pete

Bad plan. Do not remove the throttle stop screw on an Evo 10. There will be nothing left to hold the throttle barrel in! That screw is a huge component in the function of that carb.

Throttle stop to be adjusted per the owners manual. You might want to have another look at that section. Contrary to most directions, the Evo 10 carb adjusting section of the manual is very well written!

OOPS!
Here I just rebuilt an EVO 15cc carby, (new carb body due to dirt nap) so's I shoulda known that it didn't have an idle stop screw at all.
Somehow my brain was seeing images of a Walbro style carb.
Pete

No harm done.
About the same thing just happened to me on another forum I haunt. We were talking about prop pitch, comparing it to rear end ratio's in a car or truck - and I wrote it out bass ackwards.....

Embarrassing hell, but "stuff" happens!

Also, check the throttle plate. It recently happened to me with a DLE 20. The screw in the center of the plate loosened up allowing the plate to move as if you opened it. It would throttle down to idle, then slowly creep up to like 3500 rpm. Not too easy to land like that. I had to cut the ignition on final until I figured it out. Just a thought.

And another one forgets that this isn't a Walbro style carby
The EVO 10cc carb is a modified glow carb with a throttle barrel. No throttle plate to come loose
Meir, you really need to observe what's happening with the throttle and linkage when running the engine on the ground, also your radio has a servo monitor screen that will show you if their is any erratic behavior in the throttle sticks output.
Pete

I've never had an evo. Sorry, just trying to help.

I'm not familiar with this carb and I really don't think this would be it, but does the throttle barrell have excessive sideways play?
I had this on a glow engine once, but it didn't have a huge change in rpm's like you are seeing.

There's a spring in the bottom of the hole the throttle barrel fits in (that's actually a little stronger than need be). This spring holds the barrel up against the guide pin that also acts as an idle stop. Bottom line, good idea, but not very likely that barrel movement is causing the issue with increasing idle speed.