XY Steps Problem

Ive just changed my timing belt pulleys on the X and Y to 16 tooth from 20 and the dam thing wont behave now. It's a Prusa with Ramps and Marlin. At the moment regardless of what i put in the config.h file, a 10mm movement signal equates to an actual move of just 8mm ish. This is the line of me config file:

#define DEFAULT_AXIS_STEPS_PER_UNIT {400.00, 400.00, 4266.66,200, 200} //

Ive even been silly and put 00.00 into the X and Y sections but the dam things still move just 8 mm!!!

All was working with the 20 tooth pulleys but I thought I might get better resolution with the 16s. The Ramps board jumpers are set for 16 step microstepping and the Nema 17s are .9 degree (400 step rotation) units, the belt pitch is 2mm.

Now I know one answer might be to put the 20s back on, but I took them off and modded them to fit on a new dual print head:-(

Do you have EEPROM enabled? Then you forgot to do a M502, followed by M500. Steps per mm is one of the things saved in the EEPROM.

Thanks for the reply. As it happens the problem is sorted now, but the strange thing was that it had been working for months and then suddenly packed up. Got to think it's a glitch somewhere in the firmware, why? Well I have downloaded a more up to date version of Marlin and it worked perfectly. The only problem was that it was only set up for one extruder, as soon as you said 2 it failed to compile. I spent the whole day at work today (sorry boss!) compairing the two versions and finally found the code to alter in a Pins.h file, works like a treat now