90 horse Mercury running rough..

I have a 1990 90 horse 3 cylinder motor. I've been having a problem with it running right. I rebuilt the fuel pump, took the carbs off twice and cleaned them, and still have the problem. This last time I let them soak in carb cleaner to make sure they got cleaned good, I put the carbs back on, and everything ran good, when I hit the throttle it sounded like it did when the motor ran good.

But I went to start it tonight, and the thing was running real rough again, when I gave it some throttle, it sounded like it was sucking air somewhat, and would try to die, it would also try to backfire somewhat through the exhaust. Then the only way it would start again is to keep the choke pushed in. and this is when the motor is warm, so that shouldn't happen.

I didn't put new needle valves in the carbs, just kept the originals in there, and I didn't replace the fuel filter either. Does either one of these sound like it could be the problem?

I'm pretty much lost on this, because it runs good for awhile, and then just keeps on going back to this running real rough, and hard to start deal. I'd appreciate any help you can give. Thanks

Re: 90 horse Mercury running rough..

Take a sample of your fuel, look for water.

The fact that it runs fine right after you clean the carbs but fails shortly after is often an indication of a contaminated fuel supply.

Use a test tank with FRESH fuel, drain the carbs and try again, if it works fine then install a water separating filter before attempting to run your current fuel tank.