Mercury 115 sparks intermittently on Cyl. 3

[NTCbrand]

I have an older, probably 80's, Mercury 115 motor on my boat. I just had the packs and coils replaced by a mechanic last summer. I took it out after and it ran fine. The two times at the first of this year, it even ran great. My dilemma is this. The boat starts and idles with no problem, whatsoever. It scoots right out idling from the harbor. When I throttle down after getting out a ways the boat will not go past 5 or 10 mph and the RPM's probably don't go past 1500-2000. This is at W.O.T.. I tested the carbs with some starting fluid at the lake and they all are working. When I just got home I tested spark and it seems that cylinder or spark plug #3 are not getting any spark. Can anyone help with the issue or know a good cheap mechanic.
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[Kent]

[quote NTCbrand]

... or know a good cheap mechanic.

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Wow, you want good and cheap. A more realistic goal might be good, honest and reasonable.
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