CONTINUOUSWAVE

2007 Merc 90 hp efi 4 stroke with 100 hours on my montauk 170 has problem just leaving marina. Fires up and idles just fine. But after WOT 30-60 sec later it starts to bog down. Take it to idle then back up just fine... 30 sec later it bogs down. It does this 3-4 times then it runs the rest of the day with no problems. I replaced the fuel filters. Replaced the fuel line that was delaminating, replaced the prime bulb. Fuel is always fresh. I did find the bad Merc air filter dicentigrating and replaced that. Failing lifter or fuel pump?? It's weird that it resolves itself. Seems like maybe air in the line that clears up.

Thanks in advance.

Sounds like it goes away after it warms up? Sounds electronic, if you have changed all possible sources of fuel starvation. A sensor?

Thanks for your reply! When I fire it up it runs great. It gets up on plane and were off. Then it bogs down. I take it back to idle and then It will get back up for 15 sec and then back down. The last time it will act like it wants to bog down but wont. I can power through it and it clears up. It seems to me like air in the line?? or a pump starting to fail?

I'm not sure but as you did most of the fuel supply (with pump exception) it might be one of the coil-packs. I believe that that there was a recall on them for those years on the medium HP size Mercury 4-strokes. My 60HP was doing the same thing and after taking it to a certified Mercury dealer they replaced the coil packs (under recall warranty on 5 year old engine) and that solved the problem.

Dutchman wrote:I'm not sure but as you did most of the fuel supply (with pump exception) it might be one of the coil-packs. I believe that that there was a recall on them for those years on the medium HP size Mercury 4-strokes. My 60HP was doing the same thing and after taking it to a certified Mercury dealer they replaced the coil packs (under recall warranty on 5 year old engine) and that solved the problem.

Would your motor bog down slowly then after a short time it would run fine the rest of the day? Or was it a problem that was always there?

Sorry I just noticed you question. It was intermittent yes sometimes in bogged down and then ran fine and the other times it was at certain RPM between 2500 & 3500 rpm all day long. It was annoying enough for me to finally take her in at the end of the season a couple of years ago.