Gallant T-6 rotors slow down when both are engaged

Easy. Set engine on TDC with distributor rotor pointing at #1 plug wire. Remove holdown bolt, disconnect small wires and remove cap and slowly lift distributor up paying attention to how the rotor moves as you lift. Note position of vacuum advance and make a mark on engine where rotor is pointing as you remove dizzy. On new distributor, rmove cap and turn rotor to match the mark you made from old rotor position. Install new unit with vacuum advance similar to the old one and rotor at correct position, and as you lower unit into place insure that rotor points same as old one did before you started removing it. The one other major issue is that a points style distributor has a supply wire with either a built in resistor, or a separate resistor inside the coil. The new unit needs full 12 volts to supply it so no resistor is used. If the old unit had a coil with internal resistor and your new unit has the coil in the cap, no change needs to be made. However if the old unit used an external resistor coil, you must now run a wire from the ignition switch "on" position directly to the distributor to supply full 12 volts. All of this depends on what you are working on so now don't you wish you had told us that?

It is possible that you have a loose compensator nut. This nut also holds the rotor in place on its splines. When this nut comes loose, the splines shear and the rotor no longer spins correctly. As the rpm increases, drag also increases on the rotor so it actually slows down, lowering output from the stator. Another cause could be the voltage regulator. Listen for any peculiar noised coming from the primary. Any knocking check it out ASAP as more damage will occur.

did you turn the rotors some times there ia ridge on the rotors that needs to be machined down.

This issue is the "Drive Gear Unit" It is the small gear just above the motors which is attached to the very large gear. You will have seen several posts indicating that sometimes this gear shifts and does not engage the larger gear. In my case I looked and say that it was indeed trying to engage the larger gear, however the gear is stripped (the teeth are nearly gone). The sound that you are hearing is the sound of the gear slipping against the Bigger gear. I have a UJ365 which is a newer model. To my disappointment I cannot find a "Drive Gear Unit" anywhere on line. The copter will not function without it. This issue is that it takes the lift of both rotors to lift the copter into the air. There are two motors (one for each rotor) and each motor has one of these drive gear units. Each of these attach to the larger gears which turn the rotors. The rotors each turn in the opposite direction. This is what keeps the copter from continually turning in one direction. When one of the "main Gear Units" becomes damaged it seems to have three noticeable effects. (1) There is a noise that is the gear grinding against the bigger gear. (2) Because many of the teeth are stripped the drive gear engages the bigger bear only some of the time, this causes the rotor to turn slower and in-turn causes there not to be enough lift from the rotors to lift the copter. And finally (3), someone noted that copter wants to spin in one direction. Understanding the above, you can now understand that if one of the rotors is not reaching its full potential to turn, it is also not reaching its full potential to counter act the other fully functioning rotor. Thus the fully functioning rotor is forcing the copter to spin in its direction and the malfunctioning rotor is not spinning fast enough to stop the spin.

So this is the answer to your questions, hopefully on the older models there will be parts available for you to replace it. The copter cannot work until the part is replaced.

Check if s107 is fully charged.
Both rotors (lower and upper blade) should be working at full capacity. If either one of them is going slower, S107 won't lift up from the ground.
Check that gears are not too tight on each other. They should be able to rotate (leave cca 1mm space up/down between them)

The lower rotor has a problem where the gear on the motor shaft slides down and does not engage with the rotor gear. You can reach in through the skeleton with a small screwdriver and push the gear back up to engage. Happens every now and again, usually after a crash.

Okey, this is a trickie one, now inside the lower rotor shaft the white plastic gear goes up in to the larger shaft and has like a simi circle on top, ( i know im not discribing it well but trust me the little "tooth" most likely has broke and it randomly binds up in side the shaft, had the same thing happen to mine, i fixed it by dissembling the rotor assembly and removing the broke "tooth" and putting a drop of crazy glue on the ******!!!!!! worked for me

You need to mark in 2 places. With the cap off mark the position of the rotor button on the distributor housing first. Then you need to make a mark on the distributor housing that will line up with a mark on the engine itself.
When you put the distributor back in back the rotor button up before you put it in because the cam gear will turn it ahead as it seats. For example, if the rotor button is at 3 o'clock then back it up to 1 o;clock.
Don't force the distributor down at the end because you can damage the end that drives the oil pump. Fidle and wiggle it as you push and it should line up and drop onto the oil pump. Also DON'T turn the engine over while it's out or you will have to retime the engine. Hope this helps.

o2 censor may be dirty or need replaced

Hello;
First on the timing set, did you line up the dots exactly? You should be at #1 TDC. Set the distributor in and as it engages the cam the rotor will turn. Continue to lower the distributor until it engages the oil pump drive. When this is done, the rotor will point to #1 on the cap. Adjust your timing to specs.
Hope this helps. Let me know if you have further questions. Rate me highly.
Thanks;
Rich
RPM Northwest