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Mercury 90 hp 2 stroke losing power...need help!

C

Cumberland Mike

New member
Hello, new to the forum and the world of outboards. I have a 2005 Merc 90 hp 2 stroke outboard that has always ran well until recently. It starts good and will take off running good for maybe 15-30 seconds running about 4000 rpms. Then it starts losing power and acts like it is starved for fuel. The rpm will surge and drop between 3000 and 4000.

Running 90 octane ethanol free boat gas.

I have replaced the fuel pump, filter, spark plugs, fuel line and pump up ball. When you pump the ball while running it helps a little but not much. I suspected bad gas so I ran the fuel line into a 1 gallon can of fresh gas...no change.

Tried gas drier and sea foam, idles better but no real improvements.

Checked compression, 90-95 psi on all three cylinders.

Starting to think electrical problem instead of fuel delivery.

Any thoughts?

Thanks, Mike
 
That's not good compression numbers--I'd expect at least 130. You might have leaned it out somehow and hurt her. Sorry.


Jeff
 
Low compression wont make it surge...
If its a rapid on/off surge that's ignition if its steady down then up its fuel problem.
Clean and install kits in carbs and replace fuel supply lines,I have found several of these the fuel lines degrading internally and fill carbs with black fine particles that lean out high speed jet.
 
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Have you read the spark plugs lately,they can tell part of the story. Sounds like debris from old fuel system has contaminated your carburetors. I would follow fatzbullet's lead. BTW your fuel tank could still be contaminated with suspect fuel,you have changed everything else. Are you running a fuel/water separator along with a filter,you mentioned you changed filter? If yes, was contents dumped in a clear container,left overnite,inspected for separation, water ,gunk,etc.
 
Chris can you expand on that,lean on fuel cooking cylinders and i would imagine pistons also,does quenching come into play
 
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Like I said earlier, I am new to outboards.

All I can say for sure with regard to overheating, never ran without oil and the overheat alarm has never sounded.

The tell tale is squirting good as well.
 
Clogged carbs lean out and burn pistons. I've seen black particles in a carb base before, from a deteriorating fuel line; and this with the fuel filter only 6 inches or so from the carbs!

Jeff
 
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