2005 90 HP Yamaha 4 stroke idles rough and won't accelerate

[merk175]

I bought boat with a 05 90HP yamaha 4 stroke. The engine idles very rough and when I try to accelerate, it stalls. If I accelerate very slowly, I can get it up to max rpm. It seems to run fine at high RPM...no misfire. I'm thinking carb cleaning but not sure. I've heard that these engines have had problems because of the ethanol in the gasoline but not sure if that's true. Any suggestions? Thanks .

[robert graham]

Maybe start by draining each carb onto clean white rag just to get an idea about water or debris in float chambers, also check fuel filter on motor for water or debris. Remove and inspect spark plugs to get an idea of possible problems. Have your carbs ever been cleaned? is your gas fresh and clean?...may be time for carb cleaning. Good Luck!

[boatguy823]

well since its a fuel injected engine it could be any number of things most likely fuel related. I would start with fuel press testing, put it on a laptop making sure there are no faults.....question what is your idle rpm in neutral?....could be idle speed controller issues. Hard to diagnose over the internet.

[merk175]

this is a carbureted engine...not fuel injected

[boatguy823]

post a model number please....us market the f90 was fuel injected in 2005

[Ldavidgrover]

post a model number please....us market the f90 was fuel injected in 2005

You are correct. The 90 hp is a carb motor. If the boat has sat for any period of time the carbs are going to be you answer. Pull a drain screw of the carb and if it has any junk on it your looking at a carb job. Cross your fingers you dont have any water damage inside. NON ethenol fuel will be you best friend !!!

[boatguy823]

this thread is really irking me now.....lol. In 2005 yamaha did not make a carburated f90. I am a yamaha certified (as in master tech) tech and I can tell you an 05 f90 is a single thottle body efi fuel injected engine. It was the replacement/redesign of the CARBURATED F80/f100..but just for the sake of argument though please try to find me a part number for a carb repair kit for a 2005 f90 usa engine.

[99yam40]

Either it is not a 4 stroke, it is not a 2005, or it is not a US model

[merk175]

I tried to find a service manual for it and was told the serial number is a 2005. It may have been one of the latest 2004's built. The engine definitely has carbs...not fuel injection. I would know the difference. The boat was purchased locally (in New York) so I assume it is a US model. For the purposes of this thread, consider it a 2004 model. Back to the question....engine idles very rough and when I try to accelerate, it quits running. If I accelerate gradually, I can get it up to max RPM.

[99yam40]

F90TLRC is a 2004
F90TLRD is a 2005

Is there a reason you are not posting the model # as was requested?
Clean the carbs if it has them