Mercruiser 3.0 intermittent flooding

[BoatinMaine]

Hello. First time posting. Did some searching but couldn’t find my exact problem. I have a Mercruiser 3.0 that intermittently floods. It will start up fine and be running fine then all of a sudden a bunch of fuel will pour in through the venturis above the butterfly. The engine will run real rough with a loud air hissing noise and black smoke will come out of the exhaust. I have to give it lots of throttle so it doesn’t die. Then all of a sudden it will smooth out and the gas will stop pouring in and it runs fine. It will keep doing this randomly which is weird to me. I’ve rebuilt the carb already. Thinking it might be the fuel pump?? Thanks in advance for any help.

 

[Bt Doctur]

fuel pump should not be putting out more that 4-6 psi. more likely dirt entering the carb and jamming up the needle and seat

 

[BoatinMaine]

That’s what I was thinking. Took apart the carb and cleaned the seat and needle. Also checked float levels. What is weird to me is that it will flood for a few seconds (visually see fuel dumping out of the venturis) and then all of a sudden stop. I would think if the needle isn’t seating it wouldn’t come and go. Also checked screen filter on fuel line before carb and it was spotless. Any ideas??

 

[BoatinMaine]

Also, I did some research and if it was the fuel pump, the fuel would be entering the carb via the clear tubing from the pump not the venturis. Is this correct? Another thing I noticed is that the plate that the carb operates is not completely vertical when engine is warm. It’s close to vertical but not completely. It is still tilted a little. Should that plate be completely vertical when engine is warm? Would this cause my issue?

 

[achris]

This sounds more like the fuel pump has a small rupture in the diaphragm and when enough fuel builds up, it dumps into the carb through that clear tube you can see....

My suspicion would be more on the fuel pump than the carb.... Have a look at that clear tube, see if it has fuel in it.

Choke plate not being fully open wouldn't cause the problem, but go through the manual and set the choke up again.

Chris...........

 

[BoatinMaine]

Thanks guys. Like I mentioned before I can see the fuel coming out of the venturis and not the clear tube from the fuel pump. When I took off the tube to remove the carb, I didn’t notice any fuel in the clear tube. I did just find out that I had the linkage on incorrectly for the carb plate. I got it on all correctly now so the plate opens fully. Doesn’t sound like this was the problem but one can only hope. I will fire up the boat tomorrow to see if this changed anything. I will also pull that clear tube off to see if there is fuel in it after running it. Anyone else have any ideas?? Thanks for all the help.

 

[BoatinMaine]

Hello. Ended up taking the boat out to the lake today. The choke worked wonderfully but the short burst of bogging was still there due to the extra fuel pouring in through the venturis, just like Chris mentioned. I can definitely see the fuel coming out of the venturis when the bogging occurs intermittently. For some odd reason I totally forgot to remove the small tubing from the fuel pump to see if it was full of fuel. If it was coming from a ruptured diaphragm in the pump would I see gas coming out of the venturis? Also could this be from the air/fuel mixture needing adjustment? Thanks!

 

[achris]

With air flowing through the carb at the sort of velocities it does, see exactly where the fuel is coming from can be 'challenging'... It may look like it's coming form the venturi, it may not be.

 

[BoatinMaine]

Thanks Chris! I ended up firing up the boat today on muffs to take a look again. I pulled the tube off coming from fuel pump and put in a bottle. Fired up the boat and got it to simulate the same thing. Extra fuel was coming out of the venturis intermittently flooding the carb. I got it to do this a few times without ever getting one drop of gas into the bottle from the fuel pump. So basically the extra fuel was not coming from clear/yellow tube from the fuel pump. It doesn’t flood enough to stall the engine as long as I throttle up till it clears but definitely starts running rich and blowing black smoke for about 5-10 seconds. I also noticed it seems to happen more after shutting it down then firing it back up. Maybe just a coincidence. Any ideas? Thanks so much.

 

[achris]

Time to pull the carb again and go through is even more meticulously. If it's not the 'flooding tube', it's in the carb. (Where else could it be?)

Chris.........

 

[BoatinMaine]

Maybe adjust the float a hair more towards the closed position?

 

[Tycer]

It’s not hard to damage the rubber nipple on the float valve while setting the float.

 

[BoatinMaine]

Thanks. I’ll take a look when I double check the float level.

 

[BoatinMaine]

Update: So I took apart the carb today once again. Tore it all the way down and cleaned it. Needle and seat look great. The float level was set at 13.5mm (specs are 14mm for spring type needle). I adjusted it to 14.5mm so the needle would close just a little sooner and wouldn’t you know it!, it ran great on the muffs! I tried everything to replicate the problem I had before and couldn’t get it to happen. Hoping to take it out on the water soon to verify, but pretty sure I figured it out. Thanks for everything and I’ll post back after a run on the water. Keep boatin!!

 

[bgold87]

Check fuel pressure. I had a similar deal and I didn’t have the spacer on my fuel pump which cause to much fuel pressure. I ordered a new spacer and bam, runs great and no more fuel pouring out venturies.