200hp 3Ox66 rpm loss

[rjcamel2355]

Hey folks, got a 1999 3.1l ox66 200hp efi engine. It hasn't gave me any major issues to date. However I got on the lake today and noticed about a 6-800 rpm loss at wot, about 8mph on the top end. Got home checked the compression, 110 across the board on my China made gauge (same compression as when I bought it) I think the gauge is off. Anyways, I ran a ring free shock dose in it last trio out along with the marvel mystery oil I run in each tank. Each spark plug is black up to about th bottom 4 threads, porcelain in the center is tan with maybe a slight hint of red in it. I will get pictures in the am. Cleaned the o2 sensor last week, lp pumps replaced less than a year ago. All plugs seem to be firing. There is no miss that I can feel but these engines idle rough I know. Boat still jumps up on a plane and runs 55-58 with a full load but only at about 5100ish rpms.

I guess my question is, are my plugs possibly dry fouled with carbon? None of them were wet with fuel or oil, but they have a little over a years worth of heavy use on them.

Anything anyone would recommend? Am I looking in the right direction with the plugs?

The hint of red is running hot if I'm not mistaken, I had a poppet valve sticking but I replaced it with the mushroom style, there was never an overheat alarm and the least psi it ever had was 12psi at wot

Appreciate any and all help guys, hoping to get back in tip top shape by the weekend.

Thank you.

 

[rjcamel2355]

http://imgur.com/a/EIiNq
Compression tested as follows:
Safety lanyard unhooked
All plugs out
Cold engine (I know it should have been warm)
Throttle wide open
Cranked for 5 Mississippi per hole

Here are plug pictures and compression results, wet and dry tested (wet tested with 3ml of oil per spark plug hole via syringe). I've heard the 200s had low comprssion heads, but I'm new to the Yamaha game. The "102" is just a guess because the needle may have been a hair above the 100 mark.

Any help would be great guys. The plugs don't look too bad in the daylight. But I know something is causing the rpm and speed drop. Just trying to get to the bottom of it.

 

[rjcamel2355]

Pulled the vst and replaced the filter, checked the compression with another gauge. Around 110 psi per cylinder with a loaner gauge. Hooked a fuel pressure gauge to the valve above the vst and cycling the key I had around 38psi, when idling the pressure held steady.

I pulled all l.p. pumps and pumped the bulb, no leaking from any of the pumps. I did discover a small leak from the hose that feeds the vst from the top l.p. pump, tightened the ziptie and that problem was solved.

Is it possible I got some bad fuel?, any tips on where to look next? I just put 40gallons from the same place I've always bought fuel from. Added some enzym from Wal-Mart just in case I had accidentally ended up with any ethanol or water

 

[rjcamel2355]

Pulled the o2 sensor today, and when I pulled the sensor housing oil ran out where the sniffer tube sits. When I pulled the tube it and the hole was full of oil. I cleaned the housing tube and hole and reassembled. I haven't had time to test it. However from what I read this could be causing my rpm issue and I may also get better mpg. I mean surely if the sniffer was soaking in oil the sensor must have been seeing a rich issue? Pictures at the link below.

http://imgur.com/a/7oeQP

 

[rjcamel2355]

Cleaned the O2 sensor, and got back on the lake over the weekend, noticed a huge difference and was able to get the RPMS I was before..... for a little bit at least.... Seemed like it started to go back to where it was as the day went on. I believe I have a failed O2 sensor (or Failing). I'll try to get the volt meter out and test it on the water this weekend.

Anyone running the NTK 21006 instead of the yamaha O2, I've done some research on them, but I haven't seen any posts about the longevity, or if someone lost a powerhead over it. If it will work, I'll just replace it, if not I definitely want to thoroughly test the one I have before dropping the money for the Yamaha part.

 

[rjcamel2355]

Went out on the lake over the weekend, RPMS were at the normal range, engine ran flawlessly, still have the "raw fuel" smell (just smells like gas, not gas and oil mixed), and there is a little bit of a gas sheen on the water. I think it may be time for some new LP pumps, gonna pull them loose this week and pump the bulb and see if I notice any leaks.