flooding carb at idle

[skyking600]

My carb is flooding out at idle on an 1986 Mercruiser MCM190hp with the rochester 4 bl. it runs great when its cold and at mid to high rpm but when its warmed up at idle it floods out. when the flame arrestor is removed I can look down the float bowl vent and see the fuel level rise until comes out the vent and leaks all over, obviously flooding and stalling the engine. I took the top of the carb off and removed the needle and seat but they looked okay. The needle was a little flat on the end but the merc online catalog shows it with a flat tip so i dont think thats the problem. I didnt have this problem untill after I installed new fuel pumps s (I have two engines). The other engine runs great. Could the pressure be too high? Am I missing something. Is there a way to regulate pressure? Any suggestions would be greatly appreciated.

 

[CTD]

Re: flooding carb at idle

Is that the Qudrajet? If so replace the float they had a habit of absorbing gas and not floating too good. Another thing to check if you have it apart is between the bowl and base there is a pocket where the bowl tubes hang down into, if the tube seals (lead) seep gas will get into there and boil causing flooding. They used to make a rubber insert to put in there but you can seal it with marine tex. Just coat the lead plugs and a little around them and let it set a day before you put it back together. I'd get a kit and go through it if you've got it apart.

 

[ron7000]

Re: flooding carb at idle

Originally posted by russell baty:<br /> I didnt have this problem untill after I installed new fuel pumps (I have two engines). The other engine runs great. Could the pressure be too high? Am I missing something. Is there a way to regulate pressure? Any suggestions would be greatly appreciated.

I'm guessing they are mechanical fuel pumps. I don't think I've ever heard or seen a mechanical pump put out too much pressure. It's always too little. All carburetors need 4-9psi of fuel pressure. When you get up around 8-9 psi and more, you start running the risk of fuel pressure pushing past the needle valve and flooding the carb. It would seem most likely to happen at idle, since the engine is using minimum fuel. You need to rig up a fuel pressure gauge between the pump and carb to know. You can pick up a 0-10 psi fuel pressure guage cheap at autozone. Brass T fittings, and hose barbs and adapters can be picked up at some parts stores, marine stores, home depot, etc. If it's an electric pump, then it's most surely the problem, given your description. You can find fuel pressure regulators, marine rated even, from JEGS.com, Summittracing.com, jcwhitney. I'm pretty sure Holley makes a marine fuel pressure regulator.

 

[ron7000]

Re: flooding carb at idle

Originally posted by ron7000:<br />

Originally posted by russell baty:<br /> I didnt have this problem untill after I installed new fuel pumps (I have two engines). The other engine runs great. Could the pressure be too high? Am I missing something. Is there a way to regulate pressure? Any suggestions would be greatly appreciated.

I'm guessing they are mechanical fuel pumps. I don't think I've ever heard or seen a mechanical pump put out too much pressure. It's always too little. All carburetors need 4-9psi of fuel pressure. When you get up around 8-9 psi and more, you start running the risk of fuel pressure pushing past the needle valve and flooding the carb. It would seem most likely to happen at idle, since the engine is using minimum fuel. You need to rig up a fuel pressure gauge between the pump and carb to know. You can pick up a 0-10 psi fuel pressure guage cheap at autozone. Brass T fittings, and hose barbs and adapters can be picked up at some parts stores, marine stores, home depot, etc. If it's an electric pump, then it's most surely the problem, given your description. You can find fuel pressure regulators, marine rated even, from JEGS.com, Summittracing.com, jcwhitney. I'm pretty sure Holley makes a marine fuel pressure regulator.<br /><br />Other than that, it can also be what CTD said, or even a bad needle valve or more dirt in the carb hanging it up

 

[ron7000]

Re: flooding carb at idle

just re-read your initial post.<br />you can't tell the condition of the needle by only looking at it. Not too familiar with rochester quad's, but hold the carb with the needle and float assembly exposed, and upside down so the weight of the float pushes the needle closed. Blow into the fuel inlet port, if you can blow air in (past the needle) then it needs to be replaced. It's not sealing.

 

[ron7000]

Re: flooding carb at idle

just re-read your initial post.<br />you can't tell the condition of the needle by only looking at it. Not too familiar with rochester quad's, but hold the carb with the needle and float assembly exposed, and upside down so the weight of the float pushes the needle closed. Blow into the fuel inlet port, if you can blow air in (past the needle) then it needs to be replaced. It's not sealing.<br /><br />with the fuel pressure thing, if they are mechanical pumps or even electric and you do have pressure around 8-10psi, you may be able to drop it enough by just putting a $5 inline fuel filter between the pump and carb, instead of a $50+ regulator. hope this helps.