1985 90hp 6cylinder Mariner sputters/dies when given throttle

[Binks21]

I recently bought a 1985 90hp 6cyl Mariner outboard for my boat. Took a little gamble on it because it’s been sitting for several years. Compression is good on all cylinders. Got her mounted and everything hooked up. The motor fires right up and idles perfectly. It’ll go into gear and push the boat around at low speed 5-8mph but if I try to give it any more throttle it’ll start to sputter and eventually die. It sounds like it loses power. I have a feeling it’s not getting enough fuel. But I wanted to see what other people though first before getting a new fuel pump and lines. The carbs were taken apart and cleaned out. Only minimal gunk in the them. Fuel filter was taken off and cleaned. Didn’t have much gunk on it either. Curious what some of you may think the issue is. Any input is greatly appreciated. Thank you!

 

[Mark ofs]

Don't know if you have the same problem or not, but I have an '85 35hp 2-cyl Mercury that used to belong to my father-in-law, First trip out this year fired right up, idled good and was able to use WOT to end of lake. Drift fished for a while, restarted fine went short distance shut it off, never restarted again, had to use trolling motor back to landing. Needed new fuel pump (it was disintegrating, and had 2-short rips developing in it), new fuel tank, new fuel line w/bulb from tank to outboard, new connector on fuel line to outboard (old one was loose, O-ring had failed). Then needed to reclean the carb to get the garbage from the fuel pump. Note, not sure how old the fuel pump was, but know it was at least 18yrs....

 

[Chris1956]

So you cleaned the carbs. They now need to be adjusted to give smooth acceleration. This must be done in the water, motor warm, and I recommend fresh fuel.

Normally you start with the idle mixture screws set at 1-1/2 turns open, and richen them from there. Try to accelerate. If she stumbles, open top carb screw 1/8 turn. Repeat acceleration attempt. If she still stumbles, open mid carb 1/8 turn. Repeat with bottom carb, and then top-mid-bottom carb sequence, until you get smooth acceleration. Test after each adjustment and take your time.

 

[Binks21]

I’m at work today but I’ll take it out tomorrow and give that a shot. Thanks for the input! If that doesn’t work, I’ll replace the fuel pump and lines. I’ve spent the last 2 months working on getting the motor mounted and all the controls and electrical hooked up. Had to track down a lot of work parts. Just itching to be able to get it out running as it should.

 

[Chris1956]

If you hand pump the fuel primmer bulb, and she accelerates, the fuel pump is defective. If that doesn't fix it, rebuilding the fuel pump is a waste of $.