Yamaha 175hp, 1988, lost it's grunt past 4000rpm

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cake7

Cadet
Joined
Jun 29, 2005
Messages
9
HI, I have a 1988 175HP Yamaha outboard, bought it 5wks ago with boat, was running OK revving up to 5000rpm, started a week ago to not rev over 2000rpm. Checked fuel to Carb's was OK, so stripped Carbs down and cleaned out bowls and jets. ran fine until I noticed plug heads (Rubber) were popping off, replaced them and for the first 2mins I have never felt so much power from the engine Wow, but then after initial 2min run, it has lost its new found pep' and now wont rev' over 4000RPM, check oil, check fuel getting to carbs via semi-clear fuel filter found opposite side to throttle assembly at the bottom half of the engine (In-side cover) and full of fuel with no water present. I am at a loss as to why. I have changed spark plugs and HT Lead heads. I just don’t know why it ran so superbly and then lost its grunt. it idles OK and starts no problem, Please Please can anyone help??
 
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bigbrownbuku

Master Chief Petty Officer
Joined
Sep 17, 2004
Messages
885
Re: Yamaha 175hp, 1988, lost it's grunt past 4000rpm

a good start would be a compression test and check you are getting 6 consistent sparks.
 
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cake7

Cadet
Joined
Jun 29, 2005
Messages
9
Re: Yamaha 175hp, 1988, lost it's grunt past 4000rpm

Have checked, compression, all OK (around 115 give or take) sparks checked by looking at each plug spark and they seem strong and constant. not sure what to check next? any ideas gratefully received.
 
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Ray Neudecker

Lieutenant Commander
Joined
May 25, 2004
Messages
1,656
Re: Yamaha 175hp, 1988, lost it's grunt past 4000rpm

Run the line straight to the engine without using the quick disconnect and bypass the engine mounted filter assy. These are both causes of fuel restrictions on those motors.
 
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easygo0

Seaman
Joined
Apr 4, 2004
Messages
59
Re: Yamaha 175hp, 1988, lost it's grunt past 4000rpm

had samne problem with 1988 150 etxg screw heads inside fuel pumps rusted away from moisture yamaha would sell me new fuel pumps for like 70.00 each with new stainless screws just like thier flaw with shift rod ,I purchased stainless allen head screws from nut bolt and fastner company for about .12 cents each had to clean out debris from circuits in carbs also though.never had problem since. Good Luck
 
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