Mercury 115 hp running poorly-update

[mac_in_mt]

Update.....
I pulled and cleaned all the carbs and replaced the fuel filter.

I tested spark and compression and both seem good although spark plug no. 4 looked completely clean (no oil or carbon residue). The spark plugs were new about 3 months ago and have at most 15 hours on them.

I checked to make sure that I had reasonable gas pressure downstreeam of the fuel filter. Gas would shoot 6-8 inches out of the fuel filter while cranking the engine.

I removed the exhaust plate and replaced the gaskets.

I replaced the throttle and shift cables and while investigating the cable and throttle arm assembly I discovered that the throttle shift assembly will not fully open the butterfly valves on the engine.

I plan to follow the tune up procedures in the manual when I can borrow a timing light this weekend.

Last night I took the boat out and I am still having power problems in the top 1/3 of the throttle range. About 1/2 of the time the engine will run with full power and the other 1/2 of the time it will not. While running at WOT and with the engine not performing, it will suddenly snap to full power. The engine will run like this for a little while and suddenly snap to not performing well. To me, it doesn't feel or act like a fuel supply issue....which leads me to ask what next?

Thanks,
Pete

 

[Fed]

Re: Mercury 115 hp running poorly-update

Did you fully check the exhaust baffle plate for pinhole leaks?

 

[mac_in_mt]

Re: Mercury 115 hp running poorly-update

While cleaning the exhaust baffle I looked for an sign of leaks. I didn't see anything that would lead me to believe I had a leak issue. On the block there is a hairline crack between one water port and another water port, but I don't see any way this is letting water get back into the exhaust. I put a straightedge on the face and it is flush and the gasket butted up well against the face.