with a modded motor in the mcd baja you need to run a race/tuning clutch as the revs are too low with a standard clutch u need something like a pitstop tuning clutch which is what i run reason being the standard clutch engages at 6000 revs it needs to engage at 9000 revs i have also heard of people shaving the standard clutch to make it lighter so it engages at a higher rev
also change your gearing to 27/36/25/24 cause i take it it will be 24/39/24/25dont know why they supply it with that gearing, its way too short, the engine revs out at around 30mph. Get the 27/36 gears, then swap your 24/25 to 25/24 that will give you a top end of around 40mph & loads of torque at the low. this was advice given to me when i started runnin my mcd baja a few weeks back and it does make a difference as i run a 29cc engine in mine