Ls2000 port engine won’t rev past 6000 in water.

[JimBud]

Has anyone ever solved this issue? I’ve read 100’s of posts with others trying to resolve this, but haven’t found the solution.

Background: I have a 2001 LS 2000 that dropped an oil line and seized. I replaced the engine with a used one that had great compression (119,118,118). During the replacement, I rebuilt the carbs with Mikuni kits, installed new reeds, new fuel filters and lines, pulled the exhaust apart and cleaned them internally, sent the coil packs out and had them checked and new wires and boots installed, installed properly gapped new spark plugs, and installed new oil lines with clamps.

Right from the first startup, both engines fired well and idled properly. Once warmed up, I hit the lake and immediately could tell that the stbd engine was not having the same throttle response as port. Stbd struggled to get up into the power band and would only get there if throttled quickly and with the help of the other motor. Top speed about 46 mph compared to 51 mph before.
Rechecked throttle cable adjustment- still the same.
Swapped fuel supply lines, still the same.
Swapped carbs engine to engine - still the same (not a carb issue)
Tried another set of new plugs - still the same.

If anyone has had this issue and found resolution, please let me know how you got your boat back up to full speed.

 

[Hoppy]

What did the plugs look like you took out? Were they all about the same dark brown color or was there one suspiciously clean like a cylinder is not firing? May need to try and swap ignition boxes side to side or the stator side to side. Maybe confirm it's not a tachometer issue and swap them side to side.

 

[JimBud]

The plugs all look good /the same when I pull them, and it is definitely not the tachs - they are both brand new and set properly, and you can feel the stbd engine lag below the power band a bit until it decides to jump up to the 6k range, and the boat doesn’t get up to 50+ mph which was its norm before this issue.

 

[Hoppy]

Well if you have already swapped carburetors and fuel lines to verify its not a fuel supply issue, and you have recently and personally checked compression (not taken someone's word) to verify it's not a compression issue that most likely leaves it being a spark issue. I would try swapping ignition boxes side to side and then stator housings side to side to check the ignition it may not be working correctly at speed under load. If that don't fix it or reveal the problem I would try swapping the reeds side to side then pull the exhaust back apart and verify there is not some sort of blockage downstream of the engine and that the water ports are all clear again. It also could be a vacuum/pressure leak in the crankcase you may need to pressure test the engine but I'm inclined to say its probably not if all the spark plugs looked the same dark brown.