I recently bought a '94 17.6' Champion with a Mercury 115HP. Have had it for about 2 weeks. Motor ran good,until a few days ago. A wake boat drove in front of me and sent a huge roller towards me. I was only running around 30 and as soon as I saw it I let off the throttle but the entire boat went airborne then struck the 2nd wave when it came down. After that, I could not get on plane. I believe that this motor idles and runs up to around 1800 RPM on 2 cylinders and then the other 2 kick in. It starts and idles like normal. When I try to accelerate and get on plane I can't get full throttle and you can hear it missing and feel it get really jerky. Before this, it would jump on plane almost instantly.

I pulled the cowling and didn't see anything abnormal on connections. I checked the plugs and one looked a little fouled so tonight I replaced all four. Took it to the lake, cranked right up, idled smoothly and as soon as I tried to get on plane, I started getting the same results. I thought that maybe the prop hit and somehow damaged the lower unit or bent the shaft but I get no vibrations and checking it out of water, it seems to be fine.

What would hitting a wave do that would make it start behaving this way? I'd like to check some obvious things before taking it to a mechanic but I'm at a loss at the moment. I first thought maybe it was debris in the fuel but the carbs have just been cleaned, filters replaced, all hoses replaced and fuel tank removed, drained and cleaned and the fuel is all fresh.

Hi, I would have a certified marine mechanic check out the engine from top to bottom.
It may have been a long time if ever that the engine had a complete tune up.
I had the same thing (well almost) on a 2004 Johnson....I don't think it had ever been tuned up.
Runs completely different now, as it should.
As to the 'wake' you encountered, I don't know but the mechanic should for sure.
The man in my signature is very good but, there are others of your choosing.
Just my thoughts...
God Bless

First check and make sure all your carbs are opening when you open the throttle. I had linkage come loose on one and it acted like that. Ran fine at idle, I kept thinking it was a spark problem at higher rpms but finally figured it out.

Got it into my mechanic and he did an initial check and found that it wasn't getting spark to two cylinders. Not as bad as I initially feared. Always scary when it's a new boat and you think you may have bought a lemon.

probably a bad connection that got knocked loose

Ended up to be an electrical component had gone bad. Mechanic got it replaced and I'm back in business.