I posted a thread a while back about the RCD-3500 receiver. This receiver has an issue where if the antenna of the transmitter is too close to the receiver antenna (especially when the transmitter antenna is fully extended) it will not output a throttle servo signal (this causes the TwinSync to go into fail safe and pull the engines back to idle. You can see it with certain servos too but if servos don't get a signal for a few frames they don't move. The Twinsyncs thinks you lost your transmitter signal and pulls the engines back to idle.

I have a replacement cable to use from throttle to TwinSync that fixes this. All Twinsyncs shipping now have this fix on the twinsync itself. email me your mailing address and I will send you a cable at no cost.

You can retest it in the mean time by fully colapsing your tx antenna and stepping away a few feet to test it.