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Carb Flooding.. You gotta see this


Dudeland
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Ok so I have noticed that when I park my car for more than 15-20 min it was hard to start.  I thought it was the usual 32/36 behavior. I would have to floor it and then it would eventually catch.    It seemed to get much much worse lately, so I decided to take a close look.  I opened up the air filter and the primary throttle bore had 1cm of fuel floating on top of the butterfly valve.  

 

So the carb is new ( about 4 months old).  I set the float properly, plastic float at 35mm etc..  I am suspecting that it may be the smog do-hickey that is keeping the additional pressure in the line after I shut off the car. 

 

My car is a 1975 so it still has the device in line with the fuel line, with a Vac hose coming off it and a return line going back to the tank.  Should I bypass that and run straight from the pump?  Change the needle valve? 

 

Take a look at the video, it is kinda funny.  This is after sitting for about 20 min in a Walmart parking lot.   

 

IMG_1756.MOV

 

 

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The usual causes of that are, in some order,

 

float level set wrong,

fuel pressure too high (yes, some mechanical pumps can overpower some carbs)

float has become a sink (yes, the plastic ones can do that, too, as the foam can absorb fuel)

fuel boiling in the float bowl

Walmart

 

and indiscriminate use of insulated mattress pads.

 

Err, maybe not the last one.

 

The emission thingus should, in theory, actually HELP with overpressure if it's working right.

 

From the bubbly nature of your video, it might just be fuel boiling- a plastic isolator below the carb can help, some.

 

And your carb looked dirty in the video.  It might have just been the video, or it might be your RamFlow is flowing more than just air.

 

t

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Thanks much for the reply. 

 

The video does make it look like the carb id dirty but it is actually mint.  I am in the process of moving to an electric fuel pump and fuel pressure regulator.  I may hook up the fuel pressure regulator to see if that is the issue.  The whole carb is only a couple of months old, so I cant see the float being the issue.  Maybe a bad needle and seat?

 

I will re-check the float height and replace the needle and seat just in case. 

 

 

 

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The pressure stays in the line after the engine is shut off, unless you have the original valve (which it sounds like you do), or add something like the Jeep fuel filter, to bleed it back to the tank.

 

I did some tests with a pressure gauge and that is what I learned.  My stock pump puts out 4psi and it sits in the line after shut off.  With the Jeep filter, it drops to zero within a couple seconds.  That is the main advantage I see in using that filter.

 

I would look into why your valve is not working.

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That is exactly what my Weber did with a bad plastic float.  When I removed the carb, the entire floor of the intake manifold was a puddle of gas!

I changed to a brass float and all is well.

Re: The fuel return valve. This sends some gas back to the tank when there is manifold vacuum. This reduces the pressure/flow to the carb.

During WOT (no vacuum) it gives full pump pressure to the carb.

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55 minutes ago, John76 said:

Re: The fuel return valve. This sends some gas back to the tank when there is manifold vacuum. This reduces the pressure/flow to the carb.

During WOT (no vacuum) it gives full pump pressure to the carb.

 

Does the fuel return valve also allow the pressure to bleed off when the engine is shut down?

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19 minutes ago, '76mintgrun'02 said:

 

Does the fuel return valve also allow the pressure to bleed off when the engine is shut down?

 

Tom, I think so. 

 

When you turn off the engine (at idle speed) you would have manifold vacuum...therefore the valve would be diverting fuel back to the tank (thru a 1-way check valve) relieving pressure in the hose from the pump to the carb.

I found (through crude experimentation) the only time the return valve is closed is when there is no vacuum. Under this condition, the fuel line would be pressurized from the pump to the carb.

 

John

 

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4 hours ago, John76 said:

 

Tom, I think so. 

 

When you turn off the engine (at idle speed) you would have manifold vacuum...therefore the valve would be diverting fuel back to the tank (thru a 1-way check valve) relieving pressure in the hose from the pump to the carb.

I found (through crude experimentation) the only time the return valve is closed is when there is no vacuum. Under this condition, the fuel line would be pressurized from the pump to the carb.

 

John

 

 

Vacuum goes when the engine stops as well, so this would have to assume that excess pressure is bled off immediately prior to shut off, else the valve is closed again.

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