1997 mercury 90 hp 3 cylinder popping noise out exhaust

[Little Richard]

I'm wanting to buy this boat for 3000. He started it on muffs and it idled a little rough. He reved it up a little and when he stopped it gave out a couple of pops. I'm going to check compression, spark, timing and lower unit for water. He said he has never cleaned the carbs and says it runs like a scalded monkey. Also says it doesn't do that on the water. So what y'all think? Dirty carb or slow idle mixture screw needs adjusted

 

[Little Richard]

That is if all others check out

 

[flyingscott]

Those pops are normal when on muffs so is the idle being rougher. Take it for a test drive