I have a troy-bilt 6.75 21" push mower. We bought it two years ago and it has never start right. We should have taken it back, but to late now. We are having
Trouble starting it and when we get it start, it revs up and down the entire time.

What's it problems?

Hi,
Generally caused by a dirty carb; and rarely by a misadjusted governor.
Peace,
Clarke