mercruiser 5.0 dumps gas into carburator when shut off

[chilinose]

Bought a '92 Cobia Monte Carlo 198es with a Mercruiser 5.0 fed by a Mercarb 2 barrel. I am going to keep this question general in nature as its more of a generic type of problem in my mind rather than a carburator specific problem. I took the carb off of the boat after I bought it because it was hard to start after it warmed up,the choke was stuck open (electric thermostat style choke at top left of carb looking aft) and it wouldn't idle. I removed the carb because upon further inspection with the flame arrestor off when I shut the key off it would begin dumping fuel onto the throttle butterflys (from the mains into the veturi, not the fuel pump spill over). The carburator was rebuilt when the previous owener had the boat. I know this from reciepts and obvious new parts and gaskets.

The inside of the carb was clean, very little crud at all but I gave it a good cleaning and blow through anyway. I removed the entire choke assembly because it would not free up to the point I thought it should be. So I got that working well. Next I found the float level way off so I adjusted that thinking that may be the answer to my problem as to why it was dumping gas into the carb after shut down. While I was tinkering with it I found a great rebuild video on youtube from Mike at Mikes carburators in Wa state I believe it is. Anyways he has a bunch of videos on youtube and a websight full of carburators parts and tips. Just google him and you ll find him. In the video he mentions that rebuild kits come with both a solid and a spring loaded needle valves and if your having trouble with flooding situations go to a spring loaded valve. Well my carb has the solid valve currently in it, Im wondering if anyone has experienced this problem and remedy before. I found the part on his site very easily and ordered it since it's only $8.00 needle and seat. It was a stretch but since I am waiting for the part and I had adjusted the float I decided to put it back together just to see if the adjusted float alone fixed the problem. Well the choke works good and it idles like a top now,comes off idle nice and clean and revs up good. The flooding problem is now there intermittenly. Seems like when I shut the boat off and don't make any movement I can turn the key and with the throttle locked in the idle position it with fire right up and purr like a kitten. If I move around the boat (mind you it's on the trailer) and cause some bouncing you can see fuel again start to spill and it requires a full throttle start to get it going but again it idles fine.

Anyone ever experience this problem before? I am pretty confident this new spring loaded needle is gonna do the job I was just curious in the meantime if anyone has had this happen to them. Thanks in advance!

 

[alldodge]

Bought a '92 Cobia Monte Carlo 198es with a Mercruiser 5.0 fed by a Mercarb 2 barrel. I am going to keep this question general in nature as its more of a generic type of problem in my mind rather than a carburator specific problem. I took the carb off of the boat after I bought it because it was hard to start after it warmed up,the choke was stuck open (electric thermostat style choke at top left of carb looking aft) and it wouldn't idle. I removed the carb because upon further inspection with the flame arrestor off when I shut the key off it would begin dumping fuel onto the throttle butterflys (from the mains into the veturi, not the fuel pump spill over). The carburator was rebuilt when the previous owener had the boat. I know this from reciepts and obvious new parts and gaskets.

The inside of the carb was clean, very little crud at all but I gave it a good cleaning and blow through anyway. I removed the entire choke assembly because it would not free up to the point I thought it should be. So I got that working well. Next I found the float level way off so I adjusted that thinking that may be the answer to my problem as to why it was dumping gas into the carb after shut down. While I was tinkering with it I found a great rebuild video on youtube from Mike at Mikes carburators in Wa state I believe it is. Anyways he has a bunch of videos on youtube and a websight full of carburators parts and tips. Just google him and you ll find him. In the video he mentions that rebuild kits come with both a solid and a spring loaded needle valves and if your having trouble with flooding situations go to a spring loaded valve. Well my carb has the solid valve currently in it, Im wondering if anyone has experienced this problem and remedy before. I found the part on his site very easily and ordered it since it's only $8.00 needle and seat. It was a stretch but since I am waiting for the part and I had adjusted the float I decided to put it back together just to see if the adjusted float alone fixed the problem. Well the choke works good and it idles like a top now,comes off idle nice and clean and revs up good. The flooding problem is now there intermittenly. Seems like when I shut the boat off and don't make any movement I can turn the key and with the throttle locked in the idle position it with fire right up and purr like a kitten. If I move around the boat (mind you it's on the trailer) and cause some bouncing you can see fuel again start to spill and it requires a full throttle start to get it going but again it idles fine.

Anyone ever experience this problem before? I am pretty confident this new spring loaded needle is gonna do the job I was just curious in the meantime if anyone has had this happen to them. Thanks in advance!

Still sounds like a float level setting or the needle and seat are not closing properly. The spring loaded ones are not bad but the issue is still the same, the needle and seat is not closing off the fuel. Fuel pump pressure is only 5 to 7 psi, which isn't much. Adjust the float so it shuts the fuel off a hair more.

 

[chilinose]

What is your reccomendation as to how far to adjust the float? As I mentioned in my 1st post the vid I was watching from Mike at Mikes carburators stated each float has a certain adjusted height it should be from the gasket. How far should I go with it before it's too far? I mean because I now have an intermittent problem I tend to agree with you that I m on the right track and it just needs a bit more adjustment but thats alot to take apart just to bend a little tab. If I go to far with it Im going to shut it down early and begin starving it for gas under higher throttles no? Thanks for the advice!!

 

[havoc_squad]

The best advice is go through the Mercruiser service notice diagnostics procedure about the flooding condition.

http://www.marinemechanic.com/merc/distributors/mercurymarine/sterndrive/mercarb.pdf

It is highly possible that the carb rebuild wasn't done correctly, but the issue was ignored due to the bad rebuild was not making life completely miserable for the owner.

What I would do to get an overview of the potential root cause of the flooding issue is the following:

#1. Check that the installed needle and seat are the correct ones for the carb. Also, make sure the gasket for the seat that goes on the carb body is present.

#2. Check float level AND float drop match Mercruiser service manual specs for your model of Mercarb & engine. You are to measure the float toe position with the carb gasket on.

Float level is what regulates the fuel bowl level. If this gets out out of spec, it can cause a flooding issue at idle or the inverse it can cause a Lean condition at high speeds.

#3. Check fuel pressure level at idle going from the fuel pump to the carb. 5 to 7 psi max, any higher and you will certainly get a flooding condition caused by the fuel pump.


If none of these steps pop up, its reviewing the Mercruiserservice notice steps and the service manual from start to finish.

 

[chilinose]

Dude thats awesome!! Just the info I need bout the needle and seat and that adjustment on the eletric choke thermostat. Thanks so much for posting that to me. YOu guys have been a big help as soon as I get to work on it again sometime this week I will post an update. Thanks again!!