MerCarb Flooding at Idle

I've got a 1989 4.3L/175 HP with the 2-bbl MerCarb carburetor. It's run great until the last couple years. The problem is this - after running the boat for a while (even 15-20 minutes), bringing the throttle back to idle from anything above 1200 rpm causes the carb to flood. Even after the engine floods and quits, fuel can still be seen draining from the venturis. I have removed and cleaned the fuel tank, added an in-line fuel/water seperator, rebuilt the carb (verifying float level and drop), only to have the problem resurface a couple weeks later. The delivered the boat to the marina for diagnosing, and they rebuilt the carb again. After a month of use, same problem. The only thing I haven't done, is replace the carb with a new one, which I am very close to doing. Very frustrating getting towed in or waiting until the engine dries out. <br /><br />Any thoughts/ideas/experiences? Thanks in advance!!

Re: MerCarb Flooding at Idle

Check to see if you have a return line to the fuel tank. If you do, it could be clogged forcing the unused fuel through the carb instead of back to the fuel tank. Of course I am taking your word that the floats are in spec. Also you may want to measure your fuel pressure at the carb and make sure it is within specs. Good luck..........

Re: MerCarb Flooding at Idle

The boat runs fine when the motor is cold, so I don't think there is a line blockage anywhere. And testing it while loaded on the trailer and backed into the water will not reproduce the problem. I don't think there is a problem with vapor lock, I've never had one during the previous years, and no fuel lines were re-routed. <br /><br />How or what do I use to test fuel pump pressure? Just buy a pressure tester and install it inline?<br /><br />Thanks!

Re: MerCarb Flooding at Idle

You may have already taken care of this when you rebuilt the carb. but if not there is a service bulletin that deals with this problem. There is a solid float needle and a spring loaded float needle. I think the general idea is that the spring loaded needle valve helps prevent the flooding problem.

Re: MerCarb Flooding at Idle

I just found the service bulletin concerning the spring loaded float needle. I think I'll give that a try and see what happens. Do I need to purchase another gasket kit if I take the carb halves apart? I did have someone tell me to try lowering the float just a little bit also. Hopefully this will do it and thanks for all the help!