[RoadToad]

Could be balancing.
Yes, I know, the majority believe cart tires are too small around to need balancing.
NOT TRUE!
Jack up the front and spin the tires to see if they are out-of-round;
If out-of-round, replace them.
if not, add weight to the top side of rim when spinning tire comes to a rest.
(The heavy side will settle at the bottom).
Repeat until spinning stops at random positions.
This indicates they are in balance.
Then, swap the front tires to the rear and repeat the balancing on the fronts.
(The rear tires are the drivers and will not "free-spin"; so they need moved to the front to spin.)
Totally cured our bouncing front end.
Try it before you pounce on this; you'll learn something.