LRP sxx clogging

[grimidol]

Hi use a LRP in my dex410 when i use a 13.5 or even a 10.5 the car runs ok. When i put a 6.5 on it it runs ok in the air but once on the ground clogs stutters and will no go properly. Changed the cap still doing it. But runs fine with 10.5 and over ? am i missing some thing?