Roybob,

Welcome to the forum !

Here's my checklist:

Remove the flybar, and all the blades. Rotate with power each shaft and ensure they are true. If not; straighten or replace them.

Check the gear mesh on both motor pinions to the large drive gears; it may have changed with the motor replacement. Loosen the screws slightly, (yes, You can do it with everything assembled; just kinda have to warp the lower gear to get to the screw).

Slip a piece of regular weight typing paper in between the pinion gear and the larger gear You're adjusting; manually rotate the narrow strip between the gears; this will act as the feeler guage. Kinda press the little motor gear up against the larger gear with the paper in between and tighten the screws.

Do this on both. Now check the 'play' on both as the large gears aren't perfectly round and may still bottom out at one area and be good in another quadrant of the large gear causing a bind. If You can move the inner and outer shaft very slightly without rotating the pinion (and I mean slightly) then You are good to go.

It is important while You are down there to make sure the 2 screws on the aluminum cap holding the inner shaft are TIGHT! Twitchiness, can happen with this slipping and grabbing; slipping and grabbing of the inner shaft. The inner shaft should be flush with the plastic gear hub. If it's not, then the screws may not be holding it on the 'flat' of the shaft.

Now check the end play on the shafts. They should just barely move up and down; it's best to error slightly too loose, than too tight on this end play. Now rotate both shafts; they should move freely, the upper will seem a bit more freely.

You should have good blades, that are balanced or at least have the same die number etched in them (that means grabbed out of the same package). You can see the numbers 1 through 4 etched in the plastic in the hub area.

Make sure the flybar is PERFECTLY straight, or install a new one.

rev up the heli and adjust the upper blade tracking with the flybar ball turnbuckle, until the tips run as true as possible.

Okay, run the cooled heli for one minute on fresh battery. After the one minute, turn the gain (the little pot on the left for the gyro) up or clockwise until the tail twitches all the time, pretty much). We don't care about the nose turning tendancies right now.

Now turn the Gain down (counterclockwise) in VERY small increments, until the heli just stops twitching (except for occasionally) You do not have to turn off the heli each time for this adjustment; which is nice.

After cooling for 4 or 5 minutes; load another fresh battery and fly for one minute; after the minute adjust the other pot, until the turning tendancy stops. You will have to unplug and plug in the heli after each adjustment, for the adjustment to take.

You will never get it perfect, because of motor temps, brush wear, 4 in 1 warming up, alot of factors, but that is why You adjust it after 1 minute of flight; as You get rid of the initial battery surge, and the adjustment will be good for most of the flight.

You have new motors, and You may have to do the pot adjustments again after an hour or two of total flight time; but after that; You should never have to adjust the little pots again. So if a problem develops again; adjusting the pots again should be the last thing; not the first thing, You do.

The motors always break in unevenly and You will have more uniformity when You have 100 percent contact between the brushes and commutator.

Hope this helps.

Gary