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Mercruiser 4.3 v6 carb flooding at WOT

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captainjohnny

New member
New guy here. I just rebuilt the carburetor 2 bbl Mercarb and gave it a tune up. Took it to ramp fired up but noticed it was dripping fuel down venturi after shutting it off. So pulled carb top off and re adjusted float and drip stopped . Now I ran it around the lake and ran like a champ below 4,000 rpm. Anything above that begins to bog down. Looked down venturi as my buddy drove and tried WOT and looks like massive amount of fuel pouring in. What gives? Thanks guys.
 
captainjohnny said:
New guy here. I just rebuilt the carburetor 2 bbl Mercarb and gave it a tune up. Took it to ramp fired up but noticed it was dripping fuel down venturi after shutting it off. So pulled carb top off and re adjusted float and drip stopped . Now I ran it around the lake and ran like a champ below 4,000 rpm. Anything above that begins to bog down. Looked down venturi as my buddy drove and tried WOT and looks like massive amount of fuel pouring in. What gives? Thanks guys.
Click to expand...

Ayuh,... Welcome Aboard,.... I'd have to guess the carb is beyond rebuildin', or ya botched the job somewhere along the way....

'n Looks can be deceiving,... it takes alota gas to run at 4000 plus....

What are the spark plug colors tellin' ya the carb is doin',..??
 
Welcome aboard !

The float still floating? The one in the carb. The fuel pump giving between 4-7 psi no less and certainly no more.

Post back after you check.

What sight tube ? The return hose from the pump to the carb if you have a mechanical pump. If fuel is present in the hose the pump went.
 
Float is not set/adjusted correctly is what gives.Or bad float.Also,the niddle valve could also,be sticking.Or bad top carb gasget.
What gives is when someone takes a carb apart that doesn't know what their doing is the main factor.
Carbs can only be rebuilt so many time until junk ,unrepairable.(looks like massive amount of fuel pouring in.)
Float's set to high or bad float or dirt in niddle valve.
Here's a hint,
While the engine is running.Full choke it.The engine should die.If it don't?You either have a air or a vacuum problem.Also,niddle valve or float problem as well.I would say the carb needs tooken apart and reassembled correctly.It's not the carb.It's the one working on the carb is the real problem.What about the ball bearing under the pump spring?Did you tip the carb over and lose the ball bearing?Most carbs have a small ball bearing located under the spring of the accelerator pump.If you tip the carb over the ball will fall out of the hole.Causing this problem as well.If your carb has a ball bearing.I know Rochester & quid-jet carbs have them.Other then that,rebuild the carb,adjust the float correctly.Try it again.If it does it again.Pitch the carb.
 
Update guys: I built a special fuel line and fittings to tap into the carb and fuel pump to avoid cutting the OEM line.I hooked up my Fuel pressure tester and fired up the engine. Much to my surprise was a whopping 14psi at idle!!!! I have rebuilt 100s of these and never ran across a boat with more jacked up crap onboard in my life. Aftermarket automotive block non- Mercruiser(cant match #s for parts or year),sight tube cut at base of new fuel pump with a bolt in it, antisiphon valve punched through, large crack on the backside of the distributor, wrong set of plugs in it, and a carb dripping fuel like a faucet.... just to name a few. I suspect the former owner (Airplane Mechanic)thought that it would be ok to stick automotive parts in a marine application. I also heard through the grapevine that the previous mechanic put in a fuel pump from Advance Auto which shortly there after blew the diagphagm and the boat was dead in the water and the crank case filled with fuel. I am going to pull the fuel pump out and see what the heck he put in and see if adapter plate is missing or gaskets are missing. Thanks to all members for all your help. Oh and the float floats,ball bearing and spring in place,top gasket perfect,all of the above. I have a brand new carb for it now but I am not installing it until the fuel pressure problem is fixed! Sorry for the delay in response just trying to juggle this and a 6 week old! Thanks again guys.
Capt. Johnny
spiderman said:
Float is not set/adjusted correctly is what gives.Or bad float.Also,the niddle valve could also,be sticking.Or bad top carb gasget.
What gives is when someone takes a carb apart that doesn't know what their doing is the main factor.
Carbs can only be rebuilt so many time until junk ,unrepairable.(looks like massive amount of fuel pouring in.)
Float's set to high or bad float or dirt in niddle valve.
Here's a hint,
While the engine is running.Full choke it.The engine should die.If it don't?You either have a air or a vacuum problem.Also,niddle valve or float problem as well.I would say the carb needs tooken apart and reassembled correctly.It's not the carb.It's the one working on the carb is the real problem.What about the ball bearing under the pump spring?Did you tip the carb over and lose the ball bearing?Most carbs have a small ball bearing located under the spring of the accelerator pump.If you tip the carb over the ball will fall out of the hole.Causing this problem as well.If your carb has a ball bearing.I know Rochester & quid-jet carbs have them.Other then that,rebuild the carb,adjust the float correctly.Try it again.If it does it again.Pitch the carb.
Click to expand...
 
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