15FMH 2 stroke power issues

[ChasingEden]

A while back I had issues with a ground wire plug that connects to the pulser coil on my 2009 15FMH outboard. It corroded and broke causing the engine to run rough. I replaced the wire but didn't have a waterproof connector so I twisted the wires together and heat shrunk them. It fixed the issue. However recently I'm having issues with power from the engine. When I'm by myself or with a light load the engine runs great, has power, and gets on a plane. When I have 3 or 4 people in the boat when the engine is cold or randomly (I've yet to find out a pattern) I have full power and can plane, but it could also lose all its power and struggle even with full throttle. It doesn't run rough as it did with the broken wire I mentioned earlier, that was a noticeable rough engine even with just me, this seems to be running ok, but just no power. The other day I took the cowl off and wiggled the wires, took the spark leads off and on and when I re-started it ran normally again.

Any ideas? I don't think it's fuel-related, I've cleaned carb, replaced fuel lines, etc. It seems electronic, or a coincidence with the moving of wires, and then all of a sudden power gain.

[99yam40]

best thing to do, would be to check spark on each plug wire when the problem shows up.
if done with an inductive timing light you just clamp around the plug wire, you do not have to turn the motor off and back on while checking them.
you can also check to make sure the timing is advancing as it should when the problem shows up

If spark and timing are not a problem, then you are left with a fuel problem

[DennisG01]

It could be something else and it was just a coincidence that it got better after messing with the spark plug wires... or that certainly could have been the problem. Meaning, a loose connecter... a boot that slid part way off... "starting" to fail plug wires. Start by taking each plug wire off, inspecting it best you can (depending on your wires, you may be able to pull the connector out of the boot), then slightly crimp/tighten the connector. Check that the plug "nipple" is tight, too.