1999 Yammy 90hp 2 stroke no power in forward only.

Kyle1993

Cadet
Joined
Sep 3, 2018
Messages
7
Got a weird one that has me stumped. Motor starts and runs great just when going forward cant get past 1500rpm with WOT just sounds like its begging out. Flip it to reverse and have lots to go backwards will rev way past 1500rpm if move the throttle on carbs. Tilt the motor right up to point that prop almost breaks top of water going forward motor revs right up and shoots up 15 foot rooster tails. I have checked spark which has lots, compression on all three is all around 110psi mark, cleaned the carbs twice, cleaned the fuel lines. I'm completely stumped as to what could be causing this any idea right now is worth looking into.
 

99yam40

Fleet Admiral
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Sep 7, 2008
Messages
8,851
check to make sure timing is advancing and in spec.

more load requires more fuel and the correct timing advance
 

Kyle1993

Cadet
Joined
Sep 3, 2018
Messages
7
From googling seems to be within spec for advance. When in reverse at full throttle reverse where timing advances and hits stopper I manually moving the throttle on carbs it will continue to rev up with no problem
 

Doh

Petty Officer 2nd Class
Joined
Aug 12, 2008
Messages
187
Clean the carbs Again!. Paying close attention to the Pilot Jet next to the Main Jet in the bowl, and the jets on top of the carbs.
 

robert graham

Admiral
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Apr 16, 2009
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6,908
Same motor year and model as mine....sounds like a carb or timing linkeage issue to me. At wide open throttle with the motor turned off and the carb air box removed can you see the carb butterflies are all opening the same? I'll be very interested in what this turns out to be.....keep us posted! Good Luck!
 

robert graham

Admiral
Joined
Apr 16, 2009
Messages
6,908
Same motor year and model as mine....sounds like a carb or timing linkeage issue to me. At wide open throttle with the motor turned off and the carb air box removed can you see the carb butterflies are all opening the same? I'll be very interested in what this turns out to be.....keep us posted! Good Luck!
 

robert graham

Admiral
Joined
Apr 16, 2009
Messages
6,908
Power loss could be under-cowl exhaust leak or plugged cowl air intake.....run motor with cowl off to check these.
 

99yam40

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Sep 7, 2008
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From googling seems to be within spec for advance. When in reverse at full throttle reverse where timing advances and hits stopper I manually moving the throttle on carbs it will continue to rev up with no problem

reverse does not load the motor up like forward does
 

Kyle1993

Cadet
Joined
Sep 3, 2018
Messages
7
Tried the air cowl removal already with no difference. I can see butterflies they are synced. When I cleaned carbs last time I did take extra care to clean all the jets very carefully. Beginning to wonder about possibility of having a prop issue, it's the recomend prop for motor tho.
 

99yam40

Fleet Admiral
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Sep 7, 2008
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8,851
so this rig has never run properly?
Same motor props needs are different for different loads and boats

also did you follow the sync and link procedures after putting carrbs back on?
that does includes checking timing
 

Kyle1993

Cadet
Joined
Sep 3, 2018
Messages
7
Unsure full history of motor been working on it as project. This is the last problem I have. I just put carbs back on never played with connecting rod for the butterflies. So never did any sync and link procedures. Visually checked that butterflies were same spot and put pilot jets in spot they were before
 

99yam40

Fleet Admiral
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Sep 7, 2008
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8,851
how do you know the prop is correct for your boat,motor,and load?

Find a service manual for your motor and follow the proper procedures and specs every time you do things.

how do you know they were correct when you got the motor?
 

Kyle1993

Cadet
Joined
Sep 3, 2018
Messages
7
Lots of Google and forum reading. I have no idea what's correct from when I got it. Been trying to find service manual but no luck yet. It's why I joined forum get some other ideas.
 

99yam40

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Sep 7, 2008
Messages
8,851
Yamaha manuals are copyrighted Material and most sites frown on posting that material.

does not mean you cannot find it, just have to look up what your manual # is and do some searching
 
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