I have a HBK2 with stock TX, RX and tail servo, s3114's on the cyclic, stock gyro,
Esky 3900kv motor, Esky 25A brushless ESC.
When I plug in the battery the gyro initializes, the tail servo centers and seems
to work just fine. But when I try to take off the servo goes nuts and the heli
spins clockwise. Is this just a bad gyro?

it spins clockwise? from the top looking down? typically with a bad gyro the heli will spin counter-clockwise. And what do you mean the servo goes nuts? does it move back and forth really bad or does it just lock onto one side?

The servo moves back and forth, but maily forward. This started happening after I replaced the stock cylic servos with the Futaba
s3114's.

It started happening a couple of days after replacing the cyclic servos.
Could that have something to do with it?

Has the gyro been taken off & put back on lately? If yes, then I'm guessing its not orientated the same way.
If no, then I'd double check the switch settings, both on the TX & the gyro.
Same question about the belt. Has it been reinstalled?

Gyro Or belt hasn't been replaced.
I had replaced the stock cyclic servos with futaba 3114's, it seemed to fly fine,
just drifting a little bit so I leveled the swash, again it was flying fine when the tail
started acting like it was over-respondng to the inputs. Then it just started spinning clockwise,
(from the top looking down).
Now when the throttle gets above about midpoint the tail servo starts going back and forth
(mostly forward). The belt seems OK, switches are set right, tried adjusting the
gain, moving the servo foreward and back, tried a different servo, still spinning!!!

spinning clockwise after adjusting the swash a few times probaly means you increased the pitch quite a bit.
Too much positive pitch will not allow enough head-tail speed to hold it.
Do you have a pitch gauge to check
Pitch should be 0 at mid stick in idle up with stock radio
Brian

I think bkind hit it on the head... did you check the pitch of the blades when you put the new servos on?

The pitch was slightly off. I adjusted it, didn't help. I tried a couple of diferent servos on the tail, put the stock servos
back on the cyclic, didn't help. Could it be a malfuncioning BEC on the Esky speed controller? I've heard they aren't the best.
Any suggestions for a better speed controller?

ok...i'll chime in...spinning clockwise is highly unusual...if there's a tail problem, it usually yaws left or blows-out counter-clockwise in flight...although you don't mention changing the tail servo, or fiddling with the reverse settings, i'd take a look at the transmitter reverse/normal on channel 4...if there's a direction (normal/reverse) switch on the gyro, i'd play with that too...imho, most gross malfunctions are not equipment failures...most can be fixed by going over the mechanical setup and transmitter settings...once, i replaced the pitch servo...the test flight was horrible...i was chasing my hbk2 all over the sky...turns out the pushrod for that servo wasn't in the same hole as the aileron and elevator servo arms...dumb...good luck...ken

Don't know, but to me, if this behavior popped up in mid flight, & given all the things you've tried, I think you've got an upgrade opportunity here....
Declare the gyro dead, (or at least mostly dead) & go buy the HH gyro of your choice.
Dead or not, You'll thank yourself in the long run.[&:]

One caveat though. You mention throttle position, effects the behavior, and I can't rationalize that... What happens when you disconnect the motor?.. If the servo/gyro behavior return to normal. It might be a problem W/ the BEC/ESC circuit.

Keep thinking about your reference to throttle position.... Another test you might try is, W/ motor disconnected, bypass the gyro & plug the rudder servo directly into the rudder chanel (ch4). Then operate the throttle & watch the rudder servo. It should only respond proportionally to left-right movement of the throttle, not up-down movements. If it does anything other than that, track it down.

I disconnected the motor and bypassed the gyro, when I move the throttle the tail servo twitches.
With the gyro hooked up it still twitches, just not as much. Tried different switch settings,
still does it.

it's twitching but is it responding to input? it might be interference or receiver related. make sure the esc is as far from the receiver as you can make it and that the antenna is on the opposite side of most of the wiring. not sure if this is it but... also make sure that the receiver crystal is seated correctly.

Yes, it responds to rudder input. Will check ESC, etc.
Thanks

did you try plugging one of your 3114s into your gyro or ch4? sometimes a bad servo will cause jittering...i recommend that you have a spare servo on hand to trouble-shoot problems like this...btw, a simple and basic test of tail effectiveness is to turn the nose of the heli to the left...when you do that, the tail pushrod should move forward...with a heading hold gyro, the leading edge of the tail blades will move toward the boom and stay there...ken

just in case they got moved...
On the Transmitter switches are
Ail Normal
Ele Rev
thr normal
Rud rev
the esky gyro switch is in the rev position, and set at about 3/4 way to full + postion or even a little more.
Futaba servo on the tail with the stock transmitter will go to a full travel positon when you first plug in the battery then drop back to center when the gyro sets its self. the also tend to buzz once in while when first turned on.

If you replace the gyro and you have a stock transmitter you might think of putting in a esky head hold gyro this time. You can pick up a Esky HH for 35$ or so on ebay.

opps forgot
on the esky gyro the label should be at about a 1 o'clock positon. That is when looking at it from the top rotate the gyro itself so the little adjustment screw is at a 1 o'oclock positon as looking at the top of the gyro as a clock face (don't turn the screw!) just turn the gyro. Or think of the word Esky is at about a 30 deg angle to the right , like this "/" with the E at the bottom.

Tried moving the ESC, didn't help. Somebody suggested it could be a faulty TX.
I did the tail effectiveness test, the servo didn't respond.

aha! now we're getting somewhere...gyro's are very sensitive...if you unmounted the gyro, placed it in your hand and twisted it counter-clockwise, the tail pushrod should move forward...simple as that...imho, maybe the gyro isn't telling the tail servo what to do (gyro broken), or the tail servo isn't responding to gyro signals (servo broken), or when you plug a good servo into rx channel 4, and that servo doesn't respond (rx channel 4 broken)...i doubt that your transmitter is broken...ken