classic 50 miss power loss

Im having problems with my 87 mercury 45hp classic 50. Wouldnt run due to no spark. I replaced the switch box and runs now but with a slight miss. I took it to the lake and dies under a load. Pumping the throttle seemed to help. pumping the primer bubble had no effect. At first if I reved it in fast idle and switched it into gear quick it would run about half power for 30 sec or so then try to bgg and die. Bringing it back to idle or nutreal would keep it running. After some playing with it I would put it in gear and it would now run FULL power but again for 30 sec or so then bogg. Bogg was more time related then rpm. I went through the carbs, cleaned them and repaced all the seals. Gas is new. Good spark to all 4 cylinders. All the plugs look the same. Slightly wet with black. I would really appreciate and thoughts or encouragement. Thanks.

Re: classic 50 miss power loss

Welcome to iboats, jstringer. Have you done anything with the fuel pump? If it's weak, it might not be able to keep the float bowls filled enough for high rpm. Something to think about for starters.

Re: classic 50 miss power loss

Sounds like the fuel pumps on carbs are not working, if you did not position the carb mounting gasket correctly the fuel pumps will not operate.

Re: classic 50 miss power loss

Thanks for the responses. I havent changed the fuel pump diaphrams yet but did visually inspect them. I have noticed that the idle in neutral is high around 1500. I want to say its rich but not sure.

Re: classic 50 miss power loss

OK update I have now rebuilt the fuel pump at tested its output to be 5psi (good). Took it back to the lake and same problem. Comes out of the hole and runs great for 30 sec or so then Starves. I now say starves because the fuel filter will immediatly run almost dry when i move it back to neutral before it dies. I think the carbs are running out of fuel. Fuel filter stays full while at wot. Dosent empty till i stop. I have adjusted the floats to .25in almost parrallel. Used clear hose in several places to check for air infiltration with no luck. Please help im suppost to take her to the coast in t-8days!

Re: classic 50 miss power loss

Age & Ethonal can cause many problems in old fuel systems...when in doubt, hook a seperate fuel tank and line directly to the motor, by-passing the existing fuel delivery system. If the engine now runs fine, start looking and eliminating on the old fuel delivery system till you find the problem...
Also, may sound silly, but a friend of mine borrowed my boat last week and had the same basic problem, he called from the lake and asked what happened as the engine ran fine the week before, I asked if he opened the air vent on top of the gas cap. Op's, runs fine now.....