Holley C9AF Puking Fuel From Vent Tube

[urchinhead]

I installed a recolored and rebuilt C9AF-9510-U on my trucks 390 that I purchased from an FE forum member some time ago. From what I know the carb was never run after the work was done, and I wanted to mock it up on my truck before I swap in the 428 that is going in with the same type carburetor.

I followed the standard Holley instructions for baseline idle mixture, etc. I fired the motor twice, and
found fuel splashed on the front of the carb and intake. The third time, I watched closely while cranking, and saw a fountain of gasoline coming from the front vent tube. Before I take the front bowl apart to check the float and anything else that might be the culprit, is there something else I might want to look for?
 
Also, is the rubber vent/plunger on top of the bowl supposed to sit flat at idle?
It sits cocked at a bit of an angle, not seated, but this is exactly how it looks in the Holley photos of reproduction Cobra Jet “M” carbs.

[Tobbemek]

My first choice would bee a bad oring on N&S valve in the primary bowl. Take N&S out and change the oring and try again. If you have a new N&S with the oring that's better. I see more bad orings than N&S.

[Drew Pojedinec]

008 is the oring size.  009 fits as well and is a little snugger, but sometimes too tight. (editing this as my previous statement wasn't clear and could perhaps be misunderstood, by "too tight" I mean fitting into the bowl, NOT too tight around the needle and seat assembly)

The rubber vent should be open at idle, the thought was to vent fumes outside of the air cleaner so an overly rich idle wasn't present while the engine got heat soaked from sitting.

Be very very careful on GT and CJ carbs with the primary needle, the locknut/screw can strip out the needle threads very easily.

[jholmes217]

Last time I had a Holley (same one you are using by the way) do that, the fuel pressure was too high.  I put a fuel pressure regulator before the carb and set the pressure at 5 PSI , and no it runs great.  The fuel pressure from the new Carter fuel pump was too high.

[urchinhead]

I pulled out the needle and seat, and everything looked fine. I upsized to the 009 O ring, which seemed loose around the assembly. The motor started up right away, but was dumping even more gas than before. I’m going to let what I couldn’t wipe up evaporate, swap to a new 008 ring, and look for my fuel pressure gauge.

[Drew Pojedinec]

Sometimes it works, sometimes not.
This is where it’s nice to have an electric fuel pump to prime with.

[urchinhead]

I swapped in a new 008, and the front fuel bowl is dry as a bone. I used my remote starter trigger to watch closely as the motor turned over and found the rear doing the same thing after about 30 seconds. No luck on swapping O rings with that side, but I did notice the rear needle and seat seemed to fit a bit looser in the hole.

I need to find the cheap fuel pressure gauge I used to have or borrow one from a neighbor. I have an Airtex pump on this motor that was running the Edelbrock carb that I removed.

[urchinhead]

I purchased a low pressure fuel pressure gauge this afternoon and started up the motor. With the fuel line disconnected from the carb, and a gauge on the line, it fired right up, and ran great until exhausting the fuel in the carburetor.

Just over 7 psi.

Any recommendations on a different fuel pump or particular regulator?

[Drew Pojedinec]

I use the QF billet regulators. They are expensive but seem to work with both electric and manual pumps. I regulate to 4.5psi unless it is a racer.

Now that Holley bought QF I can’t say if the regulators are still as good.

[Tobbemek]

Check that your sec. float is ok hade to change a few lately, brass ones. Doesn't  take much fuel in them to make the carb flood.
Otherwise change the N&S valve, should hold 7 psi if its not a "big" race typ, they are alot more sensitive to fuel press.

[machoneman]

7 psi is ok for race stuff but I'd regulate down to 6.5 or lower for a daily driver.

[Barry_R]

Once upon a time the Holley o-rings were a unique size with a bit thicker cross section.  Seems like everything went to the universal number sizing now - and I often see the same sort of problems.  Wonder if the bore the needle & seat assembly goes into was a different size back in the proverbial day.

[Tobbemek]

7 psi is not ok for race stuff, if we are talking about .130 N&S size race stuff for example, they need lesser pressure because they have a bigger area that meets the fuel head from the inlet. A lots of mechanical HP type like Carter and other i have seen on street cars fluctuate up to 9psi ore even more, the smaller the needle valve the higher pressure it can stand. Know Holley don't recommend any higher than 7psi, and other carbs are even more sensitive than that. There is hot roders all over the world getting away with mech.pumps with to high pressure with out knowing it.
I don't believe you have to mess whit the fuel pressure, just check your float and if ok change your N&S. Some one have checked the fuel level, right?

[machoneman]

Sorry, as I said we ran a 7.0 and no more for years on winning SS/B cars. Keep in mind that fuel pressure, like float level, is a tuning aid if with one's carb set-up is 'right'. Perhaps a real pro can look at your setup. 

[Tobbemek]

Check your float and if ok change your N&S and ofcause set the float level.

  On a race setup its better to have .130 ore bigger N&S, depends on the fuel demand and lower the fuel press to 4.5 psi just to avoid airiation in the fuel bowl. There are som movie clips from what happens in the fuel bowl in a drag racing situation, pretty amazing to see the airiation and and fuel slosh inside the bowl.

I don't use bigger N&S than .097 on street stuff if its not a really high horse power deal,  just for reliability and recommend no more than 5-6 psi if its regulateable.
The fuel level in the bowl has a more pronounced effect on the smaller throttle openings/ lower rpms than at WOT, namely when the mainsystem starts to take over from the Tsl.