Loosing power at full throttle

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phillipdi

Seaman Apprentice
Joined
Oct 1, 2011
Messages
30
I have a 1999 Mercury 90 hp. I just rebuilt the carbs and the fuel pump. I have adjusted the carburetors and got them InSync but When I took it out to the water yesterday it started just fine and Idoled fine but when I went to full throttle I lost about 10 mph and it took a long time to plane out. Loss of power. Is there anything else that I need to do because now I am stumped.
 
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Maxz695

Guest
Re: Loosing power at full throttle

Did you check to see if the carburetor butterflies where both opening fully? Where the needle and seats replaced too or just gaskets and a cleaning?
 
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Dave1027

Lieutenant Junior Grade
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May 25, 2010
Messages
1,078
Re: Loosing power at full throttle

To add,
Describe the cleaning/rebuilding procedure. Did you soak each carb in solvent? Use air compressor on orifaces? New gasket kits?

Go to full throttle and have someone squeeze the primer bulb. Any change?

Try loosening the fuel pump from the motor by the two screws. Do not disassemble the pump. Pump up primer bulb good and hard. Is the fuel pump leaking? Was the fuel pump secured tightly to the motor?

Pump up primer bulb. Drain each carb of gas by removing the bowl plug into a container one at a time. Note how much fuel come out of each.
 
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CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
Re: Loosing power at full throttle

phillipdi said:
I have a 1999 Mercury 90 hp. I just rebuilt the carbs ...................it took a long time to plane out. Loss of power. Is there anything else that I need to do because now I am stumped.
Click to expand...

Before you took the idle mixture screws out did you turn them IN until lightly seated while counting the exact turns so that once finished cleaning you could put them back exactly the same?

A slightly lean idle mixture will reduce acceleration power and on those carbs that use BOTH an idle and main at WOT, will be slightly lean at WOT as well, reducing total power by a small amount.

Idle mixture must be adjusted slightly richer than 'Best Idle Speed' while the boat is IN the water and IN Forward gear to provide the correct load and exhaust back-pressure. Final idle mixture setting may be near 1/8 turn richer than 'Best Idle'.
 
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phillipdi

Seaman Apprentice
Joined
Oct 1, 2011
Messages
30
Re: Loosing power at full throttle

I adjusted my throttle cable just a little, because I think when i was putting the carbs back on that I might of moved that cable a little and maybe messed up the timing on it. Anyways put the boat in the water cranked up it was idiling a little high adjusted the carbs a little and tested it out. I had a lot more power this time. It was almost like it was before. hole shot plane was about 2 seconds now its about 6. I am still loosing about 8 mph but I can live with the way it is now. So I guess I just need to tweek it or should I just leave it alone.
 
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