micro motor with ezrun speedo

[gerbil]

hi im in the middle of setting my micro up
and im running a 25amp senserless brushless speedo 1/10
and ive got a jp 4000kv motor with this motor in runs great from start to finish
now the problem
ive tried 2 different motors now first was a orion vortex 7500kv again senserless ,but from the go it was cogging
so i took it out guessing it is to much for my speedo
so i got my hands on a nosram storm 6700kv and it still cogged but no where near as bad plus lasted about 4 mins on street then cogged and did nt want to play no more motor waas hot
so my question is is it just my speedo is not got enough amps going out would this be why it coggs on these faster motors
how ever my friend has the orion system in his now thats a 25amp speedo and a 6000kv motor which runs fine again
both the faster motors i have tried have also been brand new
any thoughts just thinking i minght get my self a higher amp speedo
anythought more than welcome cheers