90 HP Mercury 4 Stroke Outboard Bogging at full throttle

belewsonmymind · #1 August 16th, 2007, 05:26 PM

I have a 2003 90 HP 4 stroke Mercury that bogs when I take the throttle beyond 3500 RPM. When this began, the primer bulb was collapsing at the time of the bogging. I took it to the shop and they replaced the anti-siphon valve. I took the boat out to test and it ran great at full throttle for about 15 minutes before it began to bog down again. The primer bulb does not collapse anymore. It defininitely seems like a fuel starvation problem. Someone told me it might be the fuel pump. Any ideas? I just want to get on the lake and pull a tube. Help!

Bigjohn1 · #2 August 16th, 2007, 06:27 PM

It could be a few things....this engine is prone to clogged carb jets depending on use levels, last year's winter layup procedure, the locale you live in, etc. Have the carbs ever been rebuilt since you have owned the outboard? What kind of care/maintenance have you given the motor?

belewsonmymind · #3 August 17th, 2007, 10:28 AM

I've owned the boat since June. The carbs have not been rebuilt that I'm aware of. What would cause the carbs to clog? How can I avoid in the future? Thanks!

belewsonmymind · #4 August 21st, 2007, 05:52 PM

Turns out that the fuel filter was put in upside down and causing the fuel restriction at full throttle. The mechanic told me that one of the cylinders was flooding at idle and when the engine was turned off, but he said that if I wasn't having trouble cranking that I shouldn't worry about it. He said it would likely cost over $750 to rebuild the carb. Do I risk breaking anything leaving this unresolved?

Bigjohn1 · #5 August 21st, 2007, 06:34 PM

Your mechanic has me confused. What fuel filter was installed upside down? The little plastic factory filter under the cowel only goes on one way (its a press fit on the plastic mounting flangewith screw-on site bowl).

To get a CARB 3-star rating on your engine, Merc had to put very small jets in the carbs. There have been some issues with carbs plugging up but it seems to be confined to folks who rarely use the boat and/or who don't do proper lay-up procedure before tucking the boat away for winter.

You can avoid most carb problems on this engine by using Quickleen additive in your fuel about every other tankfull of gas.