While working on the car today I noticed a little vapor coming out the primary float bowl vent on my
750dp Holley. When I put my finger over the top of the vent I could feel a slight amount of pressure blowing out.
Then I put my finger right on the vent and fuel immediately shot out the pump nozzle and flooded
the engine, sure enough there's a build up of air pressure in side the bowl. Where could this pressure
be coming from? The float level is fine and the car is running good and the secondary bowl is
ok. I put a new set of gaskets and a new power valve in,but it made no difference. Any Ideas?

Try new needles & seats, check fuel pressure, a heat sheild between the carb & the intake manifold, it keeps engine heat away from the carb. Recheck float level. Dave

Like he said above. Dirt could cause a poor jet/rod contact and allow the flooding you experienced. Why it is haveing too much pressure should be all in the fuel pump. Electric or Mech'? How much psi and where is the psi gauge? Do you have a return line?

It's like a turbo and poor hose clamps. If you push things hard enough, something is bound to leak.

let me clarify few things, the car runs fine, air pressure not fuel shooting out the vent tube.
If I take out the sight plug the fuel level is fine, but if I put my finger over the vent tube out it pours
out the sight plug hole, lift my finger off the vent tube the fuel level returns to normal .Put plug back in and watch vapor, not raw fuel coming out the vent.
The needle and seat are new and I checked for
debris twice, its clean. Perhaps I have a leak between the tank and the pump and air is getting sucked in
aerating the fuel

I had fuel vapor coming out of my vent tubes of my carb one time. Enoungh so you could actually see the raw fuel vapors like little smokestacks. :eek: Only found the cause by accident. Turned out to be a loose hose clamp back by the tank. The pump was sucking alot of air in and aerating the fuel. Put a finger over the vent tube and the car would die. I took that stupid thing apart like ten times and was almost ready to take a hammer to it. hope you find it quicker

Sounds like the fuel is percolating in the bowls.
Fuel boils at 180*. When it boils, vapor is released. When you block it's path of escape(vents), the pressure pushes it out elsewhere.
Try putting a 1/2" phenolic or wood heat spacer between the carb and manifold and insulate the fuel line.
Be sure the fuel line is not running anywhere near the hot exhaust system or headers.
You must keep ALL heat sources away from the fuel.

Randy

had fuel vapor coming out of my vent tubes of my carb one time. Enoungh so you could actually see the raw fuel vapors like little smokestacks


Steve, thats exactly whats its doing.

graemlins/thumbsup.gif Check those connections before the pump. Its always the little things that get ya huh? graemlins/clonk.gif I even had a guy at work stumped and he is a supposed holley know it all.

found a loose hose by the tank, tightened it up. problem solved.