# Yamaha 90 - 2 stroke problem..



## Sailfish236 (Jan 25, 2011)

Yamaha 90 hp, 2 stroke

I have twin Yamaha 90's, the starboard engine runs fine but the port engine is preventing the boat to get up on a plane and run properly. It idles perfectly until under a load or in the water, when I put it in gear it sometimes bogs down and dies, sometimes if I ease up real slow it will run but will not get over 15-1800 rpm's with the throttle maxed.. I pulled all the carbs and cleaned them, replaced all the fuel lines and the balls pump up nice and hard. After cleaning all the carbs I noticed that port engine also idles higher with the idle screw all the way out.
I can usually figure this stuff out but on this one I'm stumped.


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## Chapman5011 (Mar 7, 2013)

Sounds like it's not getting correct fuel. I have twin mercury 90's 2003 models. I had a same type issue last year. I could barely get it to plane. I was a few miles offshore when it happened. I had a split in the fuel line leaving the fuel pump and gas was spraying everywhere. I found some extra hose that I made fit. I always like to keep a few little pieces of fuel line in my tool bag. 30 minutes later we were off and went to the edge. 
That little small split in the fuel line would not allow the boat to plane out.


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## Deeplines (Sep 28, 2007)

1st I would check fuel/water filter. Not sure about the 90 hp but my 130's had a diaphragm that would split on my fuel pump. I would check that also. It was easy to access on the 130's. Be careful of the spring inside.

This is all after doing the post above, checking all hoses and connections.

If it is the pump they are only $40 new.


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## Sailfish236 (Jan 25, 2011)

I got it! I cleaned the carbs again and left one of the nuts holding the enriching valve loose causing it to idle high. Adding new kits today so I think that was it, the dang nut was just laying in the bottom of the enriching pump housing in the carb.. OOPS! Make sure all them little screws are tight! I mustof got side tracked HA!~


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## WhyMe (Apr 21, 2013)

I think it might be the stator.
WhyMe 
Mako My Dayo


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## chad403 (Apr 20, 2008)

If your carbs are good. Check the fuel pumps. A pin hole could cause this.


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## kanaka (Oct 3, 2007)

Sailfish236 said:


> I got it! I cleaned the carbs again and left one of the nuts holding the enriching valve loose causing it to idle high. Adding new kits today so I think that was it, the dang nut was just laying in the bottom of the enriching pump housing in the carb.. OOPS! Make sure all them little screws are tight! I mustof got side tracked HA!~


You talking about the middle carb, correct? The round black thing with the 2 silver flappers that you had to yank out of its housing?


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## Sailfish236 (Jan 25, 2011)

kanaka said:


> You talking about the middle carb, correct? The round black thing with the 2 silver flappers that you had to yank out of its housing?


 Yes that thing, now it idles perfect, but the motor is still not fixed 
The motor idles, revs up good, goes in gear, runs great,, but as soon as I give it gas, no power.. still at a loss. I've exhausted almost all avenues, since theres 2 motors I've switched fuel pumps, swapped lower units, swapped coils, swapped plugs, etc. none of which fixed the problem. getting good gas flow, carbs are working perfect and clean with all new carb kits etc etc.. Would the CDI unit cause the motor to not reach the higher rpms under a load, the whole problem is only when its in the water and under way or under a load. Its kindof like its in safe mode or something.. Any suggestions would help.. 

Thx


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## Sailfish236 (Jan 25, 2011)

I think its the CDI :/


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## Sea-r-cy (Oct 3, 2007)

A lot of work, but switch carburetors on both motor. That will rule out the fuel problem, one way or another. I am of the opinion that it's a carburetor problem. Probably a high speed jet clogged.


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## Sailfish236 (Jan 25, 2011)

Sea-r-cy said:


> A lot of work, but switch carburetors on both motor. That will rule out the fuel problem, one way or another. I am of the opinion that it's a carburetor problem. Probably a high speed jet clogged.


 Did that, its the CDI. Anyone have or know where I can get one that doesn't cost as much as the motor?


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