I have a VERY easy way of getting coins on cart surfer. I usually get 500+ on it, so heres my way...
1. Do MANY BACKFLIPS (down, space), then AIR-TURNS (space, left OR right)
2. Turn by going back (down, turn)
3. This one is confusing... when you turn ( we will call this turn 1), and can ONLY do LESS THAN 4 tricks ( 1-3 ), UNTIL you see a turn again (turn 2), crash. This will take you to BEFORE TURN 1! So you can do this numerous times, until you don't have ANY spare lives.
4. Go to the end.
I hope this wasn't TOO confusing. But this MIGHT help.
I MAY post a video later, on how to do it.