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twin 2007 Yamaha 150 efi

3

3B's

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One engine runs fine, the other rough idle and max of 3300 rpm. I've replaced both inline fuel seperators but not the ones in the engines. Could it be bad gas clogging? Both engines pull fuel from same tank.
 
If the engine is idling rough it could be plugged injectors. But having two f115s I can say that one can go bad and the other stay ok.........for a while. It gets mentioned everytime.......but to properly diagnose you need to monitor the fuel pressure from idle to full power under load. If it's just injectors your fuel pressure will remain constant at about 40 psi. And if its the vst filters your pressure will drop which results in the drop in RPMs.

Anytime you pull your fuel separators I think it's a good idea to pour them into a clear jar to see if you may have a dirty fuel problem. Unfortunately you can change all filters and have the problem come back if your fuel is bad. The filters on the motors are 10 micron and Yamahas fuel separator filter is 10 micron and I had enough junk get through the fuel separator filter to plug up the VSTs. I ended up putting separate Racor 2 micron filters just to make sure I had better filtration ahead of the motors than are on the motors themselves. I also had bad tanks that I had to replace.....so it might have been over kill but I wanted to make sure I was sending clean fuel to the motors.

Good Luck
 
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