leaking needle and seat

[fastback 427]

I keep on having problems with the needle and seat leaking on my fastback. When I hit the pump fuel shoots up out of the vent tube, maybe half the time. Also seems to be running rich. Pulled it out to look at it and clean it. Looks perfect. This is the third set I've replaced. They are the viton tipped needle. Carb is 3 circuit 1050 dominator built by Bigs Performance. Hp 150 electric pump, aeromotive regulator set at 7 psi, -8 line, aluminum fuel cell, filter after the pump. Wondering if I should try a set of stainless steel needle and seats? Any help is appreciated.

[My427stang]

Pull back the fuel pressure a bit

I'd put it at 5.5 or 6.0 and see how it does with a new needle and seat, don't forget you'll have to reset float levels

A a carb doesn't change it's tune with more fuel pressure like EFI, so it won't run any different once you get the float reset.  All increased pressure does is force the float deeper into the fuel to hold the same fuel level.  Very common to see over pressured plow trucks and 4-wheelers to overflow with a little bump here and there because the float can't hold it. 

Also what are you using for a gauge?  If liquid filled they can be unreliable with heat and actually show less pressure than the system is actually making, even going as low as zero if warm enough.  An old style wiggly needle gauge is unaffected by heat

[thatdarncat]

I'd also say try a little less fuel pressure, can't hurt to experiment. Also -  It only takes the smallest particle to hang open the needle. When you've changed them does it solve the problem for a short time? Maybe drain the fuel from the bowl into a clean container - is there any material in there? I'd even pull the fuel bowl and look inside. Were they new fuel lines? Chance there's residue from the lines being made? Might want to blow out the lines to be sure.

[KMcCullah]

Need new shocks maybe? Sorry had to be a wise guy.  I can't imagine hitting bumps on the road big enough to splash gas up the vent tubes unless the bowls were really full. I've had this issue with my truck but only because it was bouncing up and down 3-4 feet. Putting a short piece of fuel hose between the vent tubes and cutting a slit for air fixed that issue.

Lowering the fuel pressure will do a couple things. It drops the fuel level slightly in the bowls and leans it out slightly. Resetting the float levels after dropping the fuel pressure will lean things out a little further yet. Hope this helps.

[machoneman]

One more thing. Although it sounds like high pressure (5.5 should be fine) and the needle/seat assemblies are likely new, carefully check the o.d., very close up, of the o-ring on the brass seat'd body.

Had a situation of late with my bro's '70 Boss 302. Fuel dumping into the primaries, floats overflowing. Had a hunch and literally got out a magnifying glass. The O-rings outer surface was rough and clearly had deteriorated, which I blame on our 10% ethanol laced gas here in Illinois. I'd never had this happen before after working on Holleys for years, even old ones pulled from a junkyard.  A nicked or gouged o-ring, going in due to poor assembly, can also do the same thing. I always rub some grease on the outer portion of the ring to allow it to slide into the float's well w/o tearing it. 

[fastback 427]

Thanks for the input guys. The fuel system was new several years ago, and I cleaned Everything. Never seen a speck of debris anywhere yet. I will drop the pressure tonight and change the needle and seat as well. I did not know that a decrease in pressure will help lean it out, thanks for the tuning tip. Also I'll grab a magnifing glass and check it out, even though no ethanol has been in the car, using c12 and premium.

[rcodecj]

One more thing. Although it sounds like high pressure (5.5 should be fine) and the needle/seat assemblies are likely new, carefully check the o.d., very close up, of the o-ring on the brass seat'd body.

Had a situation of late with my bro's '70 Boss 302. Fuel dumping into the primaries, floats overflowing. Had a hunch and literally got out a magnifying glass. The O-rings outer surface was rough and clearly had deteriorated, which I blame on our 10% ethanol laced gas here in Illinois. I'd never had this happen before after working on Holleys for years, even old ones pulled from a junkyard.  A nicked or gouged o-ring, going in due to poor assembly, can also do the same thing. I always rub some grease on the outer portion of the ring to allow it to slide into the float's well w/o tearing it.

I recently changed my needle and seat o-rings out for these:
http://www.amazon.com/gp/product/B000MN6J8C/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1