150 merc fuel issue

[mickab]

hey all, I have a 1994 mercury XR6 150. it has ran great for awhile but lately it has been dying after idling for a few min after starting it up. I have to choke it then it would start up and run just fine. but the last two times ive taken it out it will not go above 4000 rpms. it will get up on plane just fine, but as the rpms and speed increase it starts to cut out and wants to die. if I back off the throttle it will pick up and run fine at 3700 to 3800 rpms. ive replaced all the fuel lines, checked the fuel tank vents, replaced all the fuel filters and prime ball. im leaning to the fuel pump now. just want a second opinion. or if im heading in the right direction. thank you.

 

[Chris1956]

Re: 150 merc fuel issue

fuel pump is a possible culprit. If that doesn't fix it, you will need to get into the carbs and clean 'em up. You check the antisiphon valve in the fuel tank? They can restrict fuel flow.

 

[mickab]

Re: 150 merc fuel issue

ok Chris thank you for the quick response. ill check them as well. ill let yall know how the fuel pump works out.

 

[mickab]

Re: 150 merc fuel issue

ok a little update, I rebuilt the fuel pump, replaced the fuel filter, prime ball, fuel water separator and checked all the connections. still have the same issue. the original problem was that the top carb was leaking fuel when you pumped the prime ball. classic stuck needle valve. which their was a piece of trash when I pulled it apart. while doing that I notice splits in a few of the fuel lines and replaced them. after all that was done is when I started having this problem. wondering if some where in the process I broke some trash loose that may have fallen in to the high speed jets in the other carbs. that's to only logical thing I can think of. before all that it ran perfect just leaked fuel.

?????????????

 

[Chris1956]

Re: 150 merc fuel issue

Did you check the antisiphon valve? If so, maybe you did get some trash in the jets...

 

[mickab]

Re: 150 merc fuel issue

well as far as the antisiphon valve goes I have independent tanks on the boat. one starboard, one port. both have separate fill and vent tubes. engine acted the same on both tanks. so figured I could rule that out. but I did check them anyway. well will try the carbs. I might get lucky and that's what it is. thank you again

 

[mickab]

Re: 150 merc fuel issue

ok its been a bit but got it figured out. while I was changing the fuel lines on the carbs the inside of the old fuel lines were brittle and had broken small pieces of dry rotted fuel line into the bowls of the #2 and #3 carbs. (fuel delivery lines on the starboard side of the carbs) which when primed and started the next time, cause the pieces to get suck up and create a blockage behind the needle seat. so the bowls would fill up at idle and run fine until the fuel demand went higher and they could not allow more fuel flow. such an easy thing to miss but very critical thing to check. thank you all that helped and I hope this helps others with the same issue.