XRAY - Model racing cars

after testing it on track it does not seems to effect on handling.
I felt like it disappeared after 4 runs. I find the good setup and was able to take back the EPA to 65%. I think that caused to disappear the problem.

I used the foam setup come in the box (except xrc and wide topdeck ) with some small adjustment

At home I could reproduce the problem and it getting worse when I increase the EPA.

I took a video of it, I don't know if it helps. It is 12Mb I could upload to any ftp server. Send me a PM if you know any servers which allows to upload it.

Tuesday is our club racing day, I will report what I experienced in racing conditions (stock unfortunatelly)

After I raced yesterday I changed my mind.
The belt vibration is very bad now. We had a midspeed sweeper in the yesterdays layout and my car had no punch in it. I lost the battles mainly there. The belt looks to be damaged (after 10 run) and I've found black sludge on the motor pinion which shows that the vibration is very heavy and sometimes it touches the gear.
Do you think that immersing the belt in WD-40 could cure the problem? (however I don't know how to clean it after the immerse)
Or shimming the front diff?? (it has 1mm play - at least)
I realized that the manual suggested front belt tension adjustment gives a tight belt - more tight than the old car had. Can it be that the too tight belt is one of the reasons?

I am confused why your diff is moving about so much ? Mine aint, and i don't have wheel wobble like i used to with the new car.

I realized that the too stiff belt forces itself to move to the very rigth (edited) of the pulley. It even touched the right diff cover. I loosened the belt and the effect is faded. It was kind of a surprise for me since I used the manual suggested position for the excentric holders. And on my previous xray cars the default setup gave a more loose belt. It is my mistake that I didn't checked it before the test.
Tomorrow I go to test it again with the new loosened belt on the same track so I will be able to compare the times (and the feeling). Can't wait .