Itermittent power loss

[adam_p]

2013 300xs 1E051980
28 bravo xs 5950ish rpm loaded heavy, I've never aired it out solo and running light
Brand new Interstate 31MAGM battery with the recommended clamp on connectors
Brand new plugs gapped to .044
Smartcraft gauge
Fuel was drained and replaced with fresh fuel just in case
New filters were supposed to have been installed at the shop last week

Alright so here is the issue. First run off the trailer, let the boat warm up, gets on pad with no issues, no sputtering, no lack of power, I ran down the lake at about 3800rpm for about 5 minutes then punched it, ran to around 5600 rpm then drops in power, I back out go a litter farther and try again, it pulls for a bit then power drops again this time a little sooner. I turned around, took it easy for a bit then tried again, got to around 5600 again before it the power loss starts, I backed out waited a bit and then tried again with the intention of holding the throttle down to see what it does, this time it started pulling power around 5000 and just kept losing RPM while I held the throttle down, so a I backed out waited a minute then tried to video the tach. That video is attached. The variation in RPM is not me with the throttle. I'm trying to drive and video at the same time so it isn't great. This is the second day I've had it out trying to figure this out, I thought the new battery and connection was going to fix it but no luck. Both days I've been out the problem gets worse the longer I run the engine, by worse I mean it starts losing power at lower RPM. Both days the first run it pulls to 56-5800 before it starts losing power, subsequent pulls are almost always lower RPM.

I pulled the plugs just to see what they looked like. They are laid out in the order they came out of the engine. The right side of the pic would be the top of the engine. The ceramic on the plug from the top right cylinder is darker than all the rest.

Coil going bad?
Fuel getting restricted somehow?

[lpugh]

Do not run this motor until the problems is identified, The pictures are not real clear. It does appear to me that it may be very lean and I think I see some signs of detonation and excessive combustion temps. Your symptoms also fits to serious fuel starvation. The spots are very concerning. Is there also a yellow hue on the porcelain around those spots. Never try to force two stroke running that way. just begging for complete failure
Also clean those plug wire boots or replace the wires, they are candidates for carbon tracking and be sure the spark plug socket is clean
Fuel/air pressure test on the water may be in order

[EuropeanAM]

Leon- I think what you're seeing on the ends of the spark plugs is carbon (you can also see it on the porcelain of the upper set of plugs).

I do agree that this really does act like a fuel starvation problem. Simple, Quick method of determining: Connect a portable fuel tank (strapped to the back deck) with it's OWN fuel line and bulb, straight to the fuel pump inside the cowling. Plug off the original line.

Go run the boat and see if the problem persists or ceases. This quickly tells whether the problem is inside (or outside) the engine cowling.

[lpugh]

I am sure it is carbon, that many times is disloged by detonation and high temps, a yellow hue on the porclien would confim that as well as almost blistered appearance in spots on the cone. It is really difficult to read plug with pictures some times

[adam_p]

I took it in to the mechanic today. He thinks fuel as well. I'm just hoping it doesn't cost me both arms and legs now.