1) Try alt.home.repair, which has many helpful people who
should provide some good advise. There are folks who
visit rec.gardens and are good with questions such as yours,
but there are better venues for your type of question.

2) You purchased a used mower which is relatively new.
Did it ever run correctly for you? You may need to take it
to a repair shop since the mower could have a difficult-to-
diagnose problem which caused the previous owner to
sell it.

3) Do you know the previous owner? The mower could still be
under warranty and he could take it in for free diagnosis and
repair.

Good luck,
Gideon