got me puzzled...

[Mad-Dog]

My neighbors truck quit running so went over to fix it, when he cranks the engine fuel sprays out the front float vent on a single-line, dual-feed holley 600......so i checked the float level and it's ok, rebuilt the carb replacing float valves at both ends (still shooting gas out front bowl vent) , replaced front float bowl and double checking float level (still spraying gas out vent)
I have checked everything....so i start thinking that maybe the fuel pump bypass has failed and too much fuel pressure is present at carb and overcoming the float valve so we replace the fuel pump (still spraying gas out front float vent)
I'm at the end of my rope with this thing.......i have thought of every possible scenario theat could cause but i am still missing something ....got any ideas?

 

[nvrenuf]

Are you sure the floats themselves are still good? Even if they are set correctly, if they are sinking that would cause what you're experiencing.

 

[Mad-Dog]

i replaced the float.....

 

[big83chevy4x4]

what about the needle and seat?

 

[diesel4me]

mechanical pump??

It could be excessive fuel pressure,if your sure the float is set correctly and is not sinking...only way to tell is to splice a "T" fitting into the fuel line and add a test gauge...one of those fuel pump/vacuum gauge testers cost about 10-15 bucks at parts stores..

Only reason a mechanical pump would make too much pressure if if the diaphram gets old and hard,or if the pump has too much "stroke" on the pushrod...you can add gaskets between the block and pump if thats the case,but I've never had to do that on a chevy motor!--usually the pump itself is to blame if the pressure is too high--is it an old,original looking AC Delco fuel pump??...

 

[Mad-Dog]

yes i replaced the needle n seat (float valve)....

 

[Mad-Dog]

Replaced the original pump with another factory pump, no change....
Replaced the float and rechecked float level, no change.....
Replaced the float bowl, float, needle n seat and rechecked float level again..............No frikkin change

I'm missing something here, well I'm on my to California then back to Florida so i got plenty of time to ponder while i take a break here in Albuquerque,NM

 

[3 on the tree]

Try replacing the power valve. Holleys are famous for blowing them.

 

[nvrenuf]

I as I understand it, a blown power valve would only cause the idle mixture to be too rich. I don't think it would cause this type of back pressure like problem.

Mad-Dog, what about a restiction/blockage in the crossover tube?

 

[Mad-Dog]

Agreed, i have already ruled out a blown power-valve..........

The transfer tube was checked when i pulled the carb apart,
i have been thru this motor top to bottom, valve and ignition timing,
pulled the covers and inspected the valvetrain.

I appreciate all the help guys, i wanted to kick this around a bit while
I'm out here on the road so maybe I'll have some fresh thoughts when i get back to the house in a week and a half.........

 

[rumbly truck]

Does it have a catalytic converter? The only thing I could see is either it has too much fuel pressure, or, walk through this with me. Could it have back pressure in the intake. If it did could it bleed enough through to the mixture screws. How much blowing fuel are you talking about? Do you have acess to any clear sight plugs? Maybe you could see if the bowls are being taken over by fuel. Did it just quit running all at once? have you put a vacuum gauge on to see if there is poitive or negative pressure in the manifold? Got me thinking too.