Low RPM in water--RPM good when flushing!?

[xoomer]

I have a 2002 LX 2000, 2-stroke, that I started having problems with one engine yesterday. Suddenly I noticed that I couldn't get the starboard engine over 3000 RPM and it was running badly. However, when I got back to my dock I couldn't find any trash after pulling the clean-out plugs and when I hooked it up to a hose to flush it out it ran perfectly.

I took it out this morning to try the "reverse" trick to clear out any trash but it didn't help; also, I used my laser thermometer to see if this engine was any hotter than the "good" one, but they were basically the same temperature.

Does anyone know why the engine would run so rough when in the water but so good when flushing it out?

 

[davel501]

Sounds like a load vs. no load scenario. Have you tried changing out the plugs?

 

[xoomer]

Sounds like a load vs. no load scenario. Have you tried changing out the plugs?

@davel501 Well, that's what it was! I switched the plugs and then the "bad" engine worked fine and the "good" engine started sputtering. I changed the bad plugs with some new ones and took her out for a ride and both engines were running great. Thanks a lot for the help...

 

[piper84]

Similar issue full rpm on land only 3000 on water. Changed plunges and the same issue. my low oil light is flickering on fuel gauge can the circuit have any thing to do with rpm reduction. Our an ignition issue?

 

[davel501]

Similar issue full rpm on land only 3000 on water. Changed plunges and the same issue. my low oil light is flickering on fuel gauge can the circuit have any thing to do with rpm reduction. Our an ignition issue?

You need to figure out that oil light before you run it more. If oil is full and the right color and consistency then work your way back from the engine squeezing the connectors together.

These plugs are amazing if you have a tank full of bad gas but that won't help today https://rivaracing.com/brisk-multi-spark-plug-yamaha-18l-engines-er14zs.html. That very back plug on the engine tends to get the worst of it on my boat. Some carb cleaner may bring it back enough to tell you if it's fouling plugs.

 

[piper84]

Found an oil line disc from pump for aft cylinder oil issue solved. Good thing is aft cyl and mid cylinder not firing So no cylinder and ring damage I hope. Any way to ck coil packs for an open circuit.

 

[piper84]

Should I go into the box and look for corroded or oxidized connections?

 

[davel501]

Should I go into the box and look for corroded or oxidized connections?

Based upon what you've found, my next step would be a compression test. You can probably pick up a cheap compression testing set at Harbor Freight if you need one.

 

[piper84]

Eng passed a compression test 110 psi each cyl seams like very weak spark at plugs when turning over Eng.

 

[davel501]

How does it run in the water now?

 

[piper84]

Still only 3000 rpm full throttle middle and aft plugs clean no burn like the fwd plug

 

[piper84]

I’m going to ck fuel impulse pump vacuum lines see if fouled our kinked

 

[piper84]

Looks like the Eng may have a leaking head gasket powder deposits in intake housing

 

[piper84]

Found cyl 2 and 3 coil wires burned on the inside at plug boot causing very low our no spark. Runs like almost new again after coils replaced.