1988 Mercury 90 HP runs rough across the board.

[VaBeach1234]

Hey everyone. I've got a 1988 Mercury 90 HP oil injected outboard. I rebuilt the carbs, replaced the enrichner valve, replaced the spark plugs and wires, and rebuilt the fuel pump. Before I couldn't keep it running, but after finding a broken gasket in the fuel pump and replacing it, I can keep it running now. But now it runs really rough. It can't be fuel starvation, I checked and tightened all hose clamps on the fuel system. What's next? Is the timing off? I have spark in all three cylinders. What else could it be? I'm about to give up and take it too the shop but who knows how much they will charge. Thanks.

 

[DB.Beachum]

Re: 1988 Mercury 90 HP runs rough across the board.

a broken gasket or a deteriorating gasket?parts of that gasket could be stuck in some jets in a carb or carbs, if it was on the carb side of the fuel pump,are it could be the carbs need to be serviced,Lynnhaven Botel is at 65.00 an hr,about the same with Norfolk Marine and Browning's,I'm a independent, We come to you,45.00 an hour,<br />The Boatman 397-4643

 

[bKelly]

Re: 1988 Mercury 90 HP runs rough across the board.

Have you checked the gas hose from the tank to the motor, no air leaks? Is the gas you are using new?

 

[VaBeach1234]

Re: 1988 Mercury 90 HP runs rough across the board.

bKelly, the gas is fairly new. I have a portable tank with high test in it that is over a month old, I know, shame on me, it could be newer. And the permanent tank has regular in it and is under a month old. From this site I've been told that the regular works better in outboards but I still have trouble believing that. I've checked the manual and it recommends a minimum of 86 octane. I figure if there was a maximum they would list it. To answer your questions, the hoses are in good shape and are not leaking. I have two different ones and the motor runs rough with both. As for the carbs being possibly clogged, I find that hard to believe seeing how I just had them apart and I cleaned the heck out of them. Any suggestions?

 

[Backlash]

Re: 1988 Mercury 90 HP runs rough across the board.

Sounds like you need to go through the carbs again. Nothing you did would have changed the timing. <br />Backlash

 

[bKelly]

Re: 1988 Mercury 90 HP runs rough across the board.

VaBeach1234, I believe the reason for the 86 octane gas is a heat issue. Someone correct me if I am wrong, the higher octane gasses cause outboards to run hotter which means that your water pump and cooling system needs to be up to par.<br /><br />Was the motor running rough before the carb rebuild? It still sounds like a carb issue. Mabe a clogged jet.<br /><br />I would suggest a repair manual if you plan on doing the work yourself. I don’t want to sound like a smart a$$, it will prevent you from maybe making a mistake that could be avoidable.

 

[joe Hetz]

Re: 1988 Mercury 90 HP runs rough across the board.

Did you install new gaskets from carbs. to reed block assembly?