Running rough after warmed up

[MALI-MONSTER]

I'm at my buddy's lake with a load of 9 year olds . His boat is having issues. 1997ish Response with a 320 Monsoon. 1100ish hours. When it is fully warmed up it runs very rough. It has a hard time pulling a tube or wakeboard above 20 mph. We though cooling problem and it was going into limp mode and replaced the impeller, thermostat and cleaned the transition cooler screen. Same issue. I am now thinking maybe fuel delivery. The fuel pump does sound a bit louder than my Echelon's. Where is the fuel pump screen again? What other weekend saving tips do you guys have?

[Bozboat]

Check fuel pressure 

buy beer 

play poke man go

Edited July 30, 2016 by Bozboat
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[MALI-MONSTER]

Do you need a marine fuel pump or will an automotive one work?

[mikeo]

1100 hours? I'd check the distributor shaft bushings, I had them wear out on my '93 Echelon at ~1000 hrs... Here's a simple test: tie the boat loose at a dock (fenders out), one person gets in and starts the boat (cold or warm, doesn't matter), make sure the boat is at a smooth idle close to 650 RPM, stand up and start rocking the boat side to side getting at least 6" of vertical movement at the gunnels. If the engine sputters, RPMs change, stalls/dies, or something similar then carefully pull the distributor shaft and check the bushings. The bushings on my distributor shaft were visibly worn out. Make sure you can align the shaft exactly the way it was when you put in back in. Check/set your timing when reinstalling and you should be good to go. I had a local shop (NAPA affiliate) press new bushings on for ~$10 (parts & labor) when I discovered the problem.

If the engine doesn't show any hesitation, change in RPM, or stall when you rock the boat I'd suggest checking the injectors. Here's a good thread on injectors: