New to me Decathlon

[lenb]

Bad throttle servo,

Consider moving it off the motor box and putting it in the fuse somewhere.

[stevekremer]

The throttle and servo were not moving as the surging was taking place. I suppose we could turn off power to the Rx and see if surging stops

Steve K

[Steve P]

The throttle and servo were not moving as the surging was taking place. I suppose we could turn off power to the Rx and see if surging stops
Steve K

Hopefully you have an electronic kill that would stop the motor when Rx power is lost? Otherwise, never turn off Rx power to a plane with the motor running!

[stevekremer]

Good point Steve. I meant turn off Tx power so Rx holds position

[lenb]

There is an On/off switch mounted on the side of the fuse, sometimes they go bonkers and short out at certain vibration settings, Bypass the switch and try it. ( or insert another one in place of it)
If it still does it and you're certain the servo is fine, then its best to confirm carb settings are ok.

Reset the carb to factory settings.. Turn in the needles until they stop, then reset the high to 1 1/2 turns and the low to 1 1/2 turns out. ( same for both needles )

This will remove any needle imbalance that may be occurring. If its still doing it, replace both plugs, or one at a time to see which one may be bad.
If its still doing it, Its a bad ignition.

[stevekremer]

Thanks Len. I think we need to rule out radio/servo/switch, then Carb settings, then I was thinking rebuild carb (after input from Jim D). Why would you suspect plugs / ignition whan it runs so good WOT and idle?

Thanks

Steve K

[lenb]

Because they're easy things to check before rebuilding a carb.