boho - the colors on the inductor go according to the following link.
http://www.elexp.com/t_induct.htm
The colors on a 27MHz Tango-uniform controller that I have are yel-violet-gold-gold, which according to the table in the link it would be 4.7uH +/- 5%. This is similar to the value of the inductor in series with the antenna in the schematic for a 49MHz controller; i.e., 1uH.
I'm not sure about the newer cars, but my microSizers all came with the antenna toward the drivers side rear of the PCB; it is then routed to the front of the board with a knot tied in the wire and held in place by a retainer clip on the chassis, then routed back along the PCB to the rear of the car where is exits the car. I got some extra range out of undoing the knot, then routing the wire straight out the back of the car. My thougts were to get the antenna away from the board as soon as possible. It is an easy fix ... give it a shot. After fixing the antenna, tune the receiver again using the variable inductor (choke).
The sticking is the signal from your transmitter being attenuated by free-space and then reaching the controller down near the minimum triggering level (sometimes referred to as MTL). This cut-off is not a brick wall, it rolls-off, so statistically some of the signal makes it through and some does not; thus the stuttering, sputtering, sticking ... what ever you call it.
The reciever is prolly doing some DSP (digital signal processing) to smooth out the response of the car. With a faster motor the car now has more momentum and does not stop on a dime.
What you (and others) are doing by putting those 42,000 RPM engines would be analogous to putting the engine from a NASCAR into a Geo Metro ... it will go fast as he- (heck), but don't try to turn ... you'll end up on your back wondering what the he- (heck) just happened. By turning I mean, turn the wheel full right as quick as possible ... this is how the steering control works on the microRC's. If the cars had proportional control, then the car may be more controllable ... however, someone will find the 75,000RPM engine to make the car uncontrollable again. Stiffer suspension may help as well ... microSizers have a kit with three different steering control arms, use the stiffest ... I haven't tried it, yet.
I am going to make a thread on proportional control ... please check it out.
regards,
bigAL