I'm starting to get back in the R/C world. I've got a HPI RS4 Racer 2 that sat in the garage for 3-4 years and I just now got it running again. It's got a brand new clutch and brand new T15 motor.

Here's my problem:

It's got very unstable idle. It would idle fine at times, sometimes it will idle too high, sometimes it would have an erattic idle. When I brake, it would idle so low that it'll want to shut off. When it idle's low, i'll snap the throttle lightly and it'll idle fine again.

Things i've checked:

I've noticed that I've got alot of slack on the throttle linkage, about 1/8". It'll vary the carb opening alot. Should it have no play at all?
The throttle servo seems to be holding up ok, don't see the gear moving any more than the horn does.
The throttle arm don't seem like it's separating from the carb and the nut is tight. Rotary carb btw.
I've tried to adjusting the throttle linkage longer and shorter.

here are some pictures, don't know if it'll help. These pics were taken with the TX and RX on. any common things? Thanks in advance!

Probably a bad LSN problem...not to mention that you're probably running too rich. Also check if the carb opening closes a bit more when braking than when at neutral position.

I would set the Idle screw until the carb is open 1mm like the manual says. That will fix the problem of the idle getting too low when you brake

yes the carb closes a bit more when I brake. Not so much that it's completely closed but there is a hairline opening. I guess i'll just have to tune it some more. btw...how do you adjust idle? with the RX and TX off or on?

Adjust the idle using the idle adjustment screw on the carb, it may help to have the Tx and Rx switched on (at neutral) to ensure the linkage isn't holding the carb open.

OK I got the idle adjusted and it's fine now. The engine doesn't die anymore when I brake. I finally found what my problem was with the weird idle. There's too much play between the throttle linkage and the servo horn causing the engine to rev up really high sometimes. Is there another setup I can use where I can get rid of all the play? say...new servo horn and another kind of linkage where I can use turnbuckles and ball cups to get rid of the play?