Why did you slow down the fuel channel in the first place?... that would equate to opening the throttle ( introducing more air ), and then leaning out the mixture... I can understand the throttle servo slow down, but as more or less air is introduced by opening / closing the throttle , the fuel mixture needs to respond to the throttle... and fuel mixture ( air / fuel ratio ) with the fuel channel curve.

The Furtaba 18sz will allow multiple channel mixes.... the throttle stick can be setup as just a " stick position" reference only... and then the "first slave" channel to be the channel that controls the throttle servo... and the "second slave" channel to be the channel that controls the fuel mix curve ... you can either slave the fuel mix channel directly to the "stick position" channel, or to the "first slave" throttle channel... so if you put a slow down on the "first slave" throttle channel, and the "second slave" fuel mix channel is slaved to it, they will follow each other, "second slave" fuel mix channel following the "first slave" throttle channel...... or you can slave the "second slave" fuel mix channel directly to the "stick position" channel, so the two slaved channels ( throttle & fuel ) will follow the 'stick position" channel... so the slow down only affects the "first slave" throttle channel... and the "second slave" fuel mix channel follows the "stick position" channel... ... also if you put a slow down on the "stick position" channel, it effects the two slave channels ( throttle & fuel )... I found it interesting that the Futaba radio could be setup this way... but doing so you have to forfeit a channel output for the "stick position" channel