99 S150 missing, fuel restrictions, low WOT

[aluxury1]

I had headed out fishing one morning, and I could tell it was running bad from the start. This motor has always needed the carbs blown out once a year since new. So we went fishing on a sick motor, normal GPH is 8-9, now reading 13-14. Must be down 2 cyl. Got home, changed the yamaha/racor fuel water sep, changed all the fuel line and bulb from the fuel/water sep to the fitting just outside the motor. Changed the fuel flow meter. Changed the plugs, and blew out the carbs. Started it up and definitly sounded better, but not right. Took it down to the launch, ran it and never hit above 5200. After hitting 5200 it would suddenly bog to 4700. Noramlly after blowing out the carbs, I have a sweet aounding motor. I feel the only thing I can do is blow the carbs out again, but I had forgotten which gasket goes on top of the fuel filter/sep? The bead around the outside or the thick,tall one that sits farther inside the filter. I have nevver changed the little fuel filrt under the bonnet, and never changed the fuel pumps, I never had a problem. I think I am not getting fuel to one carb, or one carb is dirty. Any help here is appreciated.

[boats.net]

Could be dirty carbs, ruptured diaphram in fuel pump but do need to replace fuel filter.

[aluxury1]

Changed bottom fuel pump, blew carbs out again.

I blew through the new fuel pump and the old one and there was alot of difference. So I will change the top fuel pump also. It is not dumping fuel in the pan anymore. It still drops rmp at idle and wants to quit. I know they don't idle right on the trailer, I checked all the idle mix screwss and listened by ear and I think it slowly getting better. I will add some heat to the fuel tank and change the fuel pump and go run the heck out of it. Is there anything that is blowing the rubber gaskets on the thermostats? They were new last year and the rubber is torn on them?

[aluxury1]

Solution Found

Changed both fuel pumps! Works wonderful. Very strange both fuel pumps went bad at the same time after 12 years. Carbs are fine. Always run Sierra fuel conditioner, yamaha ring-free and a couple bottles of gas dryer nad the carbs are fine. Happy to hear the sound of 6 cylinders again!

[99yam40]

I believe Yamaha recommends replacing fuel pumps long before 12 years.
Adding "gas dryer" may not be a good idea if it is the alcohol one, especially if you are running ethanol blended fuel already. Best to drain and clean tank if water is present and fill with fresh fuel.
Also be careful running a motor that is not running properly, if it happens to be running one or more cylinders lean on fuel it will eat the pistons