2009 700. Spitting ,sputtering and backfiring?

[Misskimo]

Bought a used one. Avenger 700 kohler 26 hp
Needed bearing all around. 4 tires added.
Took it off blocks today for a test spin after all this work
Spitting & sputtering and backfiring
Parts place closed till tomorrow and ganna change the plugs
Anyone came across this kind of problem incase its not the plugs?

[Rusty-Gunn]

Our Avenger sat for a few years. The engine would not hold an idle and backfired a bit (not much though). A cleaning of the tank, along with SeaFoam additive, solved this.
I do know the Avenger you bought sat a Mavsigvik for a few years, then sat outside the hospital a few more. Maybe dirty tank? Varnish crud? Unsure though.
Maybe it hates you.

[Misskimo]

Of all things. Dirty plugs. Cleaned and ole bessy running good