Classic Engine Tech 1967 - 1981 Engine Related

newb carb question

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Old Nov 20, 2009 | 01:33 PM
  #1  
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newb carb question

I have a AED 750cfm carb on my new 408ci, and the secondaries seem to drip fuel into the motor with the engine off, fuel pump on at 4psi. Is this correct? seems like a little too much fuel to be correct. keep in mind this is with the throttle all the way closed
Old Nov 21, 2009 | 01:57 AM
  #2  
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Your rear float may not be set right. Letting the fuel bowl over fill and then it will drip fuel. Could also be the fuel getting hot in the rear bowl causing "perculation"? Not sure if that is the term for it. But basically it gets hot, expands and comes out the boosters until the fuel cools off. For a carb I think 4-7psi is where it should be.
Old Nov 21, 2009 | 09:18 AM
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Yeah check the rear float level, sounds high.. I run 6-7 psi. Also, the rear needle/seat might be sticking. Goodluck@
Old Nov 21, 2009 | 11:08 AM
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can't be that the fuel is hot bc it is 40 degrees out and the motor is off.

will check the float level once i remember how lol

thanks
Old Nov 21, 2009 | 07:30 PM
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Originally Posted by 67speeda
can't be that the fuel is hot bc it is 40 degrees out and the motor is off.

will check the float level once i remember how lol

thanks
The heat issue depends on how hot it gets on the bowl when the engine is running. It can still get plenty hot, but it is less likely this time of year lol.

To check the float level, same as the holley carbs. The brass plugs in the fuel boawls on the passenger side. Remove them one at a time (not at the same time). The fuel should just dibble out barely. (fuel should be just at the bottom of the sight plug holes).

All it takes is a sticky Needle/seat on the fuel bowl or something keeping it from closing all the way to give you all kinds of fueling issues. I know I had one stick open on my holley on a Long trip. Was literally shooting through the overflow. Deending on which you have (Since it looks like there are a few 750cfm carbs. You may need to adjust the Mixture screws in the rear metering block.
Old Nov 24, 2009 | 09:47 PM
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Yeah... my floats stick a LOT... enough to hydrolock the engine while turning it over last time. I turned the key on(electric pump) and walked around the car for a minute or so as the carb was POURING fuel down the intake.. I'd say a half gallon.. Had to pull all of the plugs and turn the engine over a few times to clear it out.. Some race fuels don't have enough lubrication in them and if the car sits for a while, the float sticks open as the fuel evaporates. In this last case it was VP C12.
Old Nov 24, 2009 | 11:38 PM
  #7  
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it stopped on its own after a few cycles of opening and closing the throttle.

I am SOOO happy to see the car on the ground (been 2ft up since nov 06) and it can be moved under its own power...

problems now:
a) car is getting HOT but half radiator is ice cold... must be air pocket. anyone have directions to pruge?
b)Horrible brakes, guess i need to put it back in the air lol
c) rough engine performance but the timing may be off. had to pull distributor to prime oil pump
d) throttle is sticking. need to fix
e) no brake lights (no pressure to the switch, can also explain poor brakes lol)
Old Nov 25, 2009 | 02:07 AM
  #8  
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Originally Posted by 67speeda
it stopped on its own after a few cycles of opening and closing the throttle.

I am SOOO happy to see the car on the ground (been 2ft up since nov 06) and it can be moved under its own power...

problems now:
a) car is getting HOT but half radiator is ice cold... must be air pocket. anyone have directions to pruge?
b)Horrible brakes, guess i need to put it back in the air lol
c) rough engine performance but the timing may be off. had to pull distributor to prime oil pump
d) throttle is sticking. need to fix
e) no brake lights (no pressure to the switch, can also explain poor brakes lol)
I would gues this is a SBC engine in the 67? Highest point is the radiator cap. I have never had a problem with letting the car run, and then when it opens the t-stat and the fluid circulates, dumping coolant into the raidator, as it would go down.

Brakes could be lots of things (Like a vacuum leak, if you have power brakes. Could also explani the carb performance.)

Engine performance could very well be the carb tune. You would have to specify what you mean by rough carb performance.

How is your throttle stocking with a carb? Do you not have the return spring on it?

Brake lights are an electrical switch, that would be something else other than preassure in your brake lines. May have to replace the switch, may have a bad ground.
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