88' 45hp mercury outboard runs great for first 10 min then bogs down when throttle up

[mcbone55]

I have an 1988 merc 45hp 4 stoke that I just got. I have run it with ears on and runs good or so it seemed. I have taken it out to the lake and it ran great right away for the first 20 min or so then would not want to throttle up. it acted like it wanted to then would bog down and only run at half to quarter speed as time went on eventually it didnt want to even idle or start. I am very new to boats and have changed the plugs and fuel filter and impeller so far. I ran seafoam in the gas so far and changed the bulb on the fuel line. I need help I am on a budget and cant take it in for a few hundred dollars in repairs at the moment. if anyone can help that would be great. I am trying to diagnose the problem and I am lost. I will watch eagerly for resposnse to this post and any questions or help would be reallllllly appreciated. thanks!

[Dave1027]

Sounds to me like a clogged fuel tank vent. Try taking the fuel cap off to verify. Does the bulb collapse? May also be a bad fuel pump. Try squeezing the bulb when it acts up. Does that help?

[BonairII]

Def try and run it with the fuel cap off. If that doesn't help, try repeatedly squeezing the bulb to get motor to pick up.

It's also possible that an ignition component(coil, etc) is heating up and failing.

[artilarygoboom]

i kinda have almost the same problem rite now, i just looked at my carbs, put it in WOT with the engine not running and noticed only one of my carbs are opening up. now i gotta figure out how to get them to open up together

[mcbone55]

I have tried to pump the bulb while its bogging and it wants to kill it. I have made sure the vent is open on the fuel tank as well. I am at a loss as to whats going on the wierd thing is that it is running really nice right out of the gate and will even run no prob at full throttle but only for about 10 min then will start to bog and get worse and worse. Would that be a carb issues? How do I know if both carbs are opening or not? still need help if anyone has any ideas thanks.

[BonairII]

My guess is that you're losing spark once the motor heats up. Maybe a coil(s) are failing when they get warm.

Hook a timing light to your motor when the motor bogs and check each cyl for spark.

It's easy to know if carb butterflies are opening.....with motor off just advance throttle on controls to full and visually check the carb to see if the butterflies are wide open.

[michaud500]

Mine does a similar thing. How about the distributor cap and rotor? Have they been pulled and inspected or replaced?

[mcbone55]

I dont have a timing light but I did check the carbs they are opening no prob took the boat out again and again first time at full throttle ran ok then started bogging again after that. I dont have a timing light to check for spark when it acts up. I will have to take it in somewhere I think. Any other do it yourself suggestions before I bite the bullet and take it in?

[BonairII]

Taking it to a mechanic will cost you a bunch of money, not to mention that your motor will probably be in the shop for weeks.

Go buy a cheap timing light at harborfreight tools. ($12-25 bucks)