Holley Carb Flooding Problem

[Jeff Kempton]

I'm posting this here as well as on the Dragsite forum.

I've been trying to help a friend fix his Holley, which is flooding uncontrollably on the secondary side of the carb. Fuel gushes out the vent tube immediately upon startup. We've gone through the expected cures with no improvement. The needle/seat was checked and changed out several times, the float was checked for leaks, the float was set to factory specs and also set abnormally low to see if that helped, and the system was checked for dirt and cleaned repeatedly. We have even switched the whole bowl assembly for another one with no improvement.

The fuel pump is a new stock low performance mechanical. I hooked an Autometer gauge to the line, and it read 7-7.5 psi. I felt this to be around the high end of the recommended pressure for Holleys, so we temporarily stuck a regulator in the system and cranked down the pressure. No change. We tried an old pump. No change.

Only the secondary bowl is flooding. We disconnected the secondary and ran the car on the primary side only when checking the pressure, and it ran fine with no flooding. I've had this carb apart so many times I'm going to start attaching the bowl with Velcro!

A couple of years ago the Holley on my car also acted exactly this way, and after chasing the problem it suddenly went away without any clear solution being identified. We've checked and double-checked for dirt and the other usual culprits. Blowing through the needle/seat while moving the float indicates that all is working according to design.

I'm fresh out of ideas. Anyone got any suggestions? Please don't bother saying to change carb brands, as this is on a restored car, and the Holley is the only acceptable option for him.

Thanks in advance for any help.

[Mitch Bonnar]

There is no way for the fuel from the fromt bowl to get into the rear bowl on a Holley so the problem must be in the rear section.
If you have changed the needle and seat and adjusted it correctly the only possible problems that I can imagine is that the float is sticking, catching on something when installed, wrong float, and the most likely cause is a sunken or fuel saturated float.
BTW..........Velcro is not gas resistant.

[Jeff Kempton]

That's why this has me perplexed, Mitch. As you've said, the problem is isolated to the secondary side. ALL related components have been changed out several times, including the needle/seat, float, and even the bowl assembly itself. The float level has been checked and re-checked, and has even been adjusted from the specified height to an abnormally low level and back in an attempt to stop the flooding and establish a baseline to work from. The float is brass and is not leaking/filling with fuel.

Correct me if I'm wrong, but flooding can be a product of only three components; fuel pressure, needle/seat, and float. All of these have been exhaustively checked with no problems identified, yet the flooding continues. HELP!!!!

[Mitch Bonnar]

I will assume that the fuel level is set correctly and the bowl itself is not filling.
If all the components have been changed including the bowl then the problem must reside in the metering block.
It is either cracked (unlikely) or the power valve is toast or falling out.

[Jeff Kempton]

No, Mitch, the problem is that the bowl is overfilling and the needle/seat/float is not closing once the fuel has reached the set level. The fuel inflow continues until it gushes out of the sight plug hole, and if the sight plug is in it'll gush out of the vent tube above the venturies. There's no shortage of fuel!

This model carb has a metering plate rather than a metering block (with jets and sometimes a power valve). I realize that most full on drag combos that you guys work with have jets on all 4 corners, but this Holley has the simpler plate only for the secondary fuel delivery. Thus there is no power valve to play a role, and because the plate is totally enclosed within the installed bowl, there are no leakage issues other than with the bowl itself.

The float is not the same one that was originally in it (which had a pinhole), and although it looked identical, I will have another look at it to confirm that it is not interfering with/hanging up on the metering plate when installed. That's the only thing that has been mentioned so far that I haven't specifically looked at.

Other than that, any other suggestions?

[Mitch Bonnar]

Hook the fuel line to the bowl with the bowl removed while holding the float in the closed position.
It should not leak by. If it does you either have a wrong or defective needle and seat or a float with a needle tab that is not compatible with the N/Seat.

[Jeff Kempton]

Done that, Mitch; and the needle/seat checks out. Even so, I swapped in two other needle/seat assemblies which also checked out in all ways. Maybe now you're beginning to understand why I'm getting frustrated!

I've done everything that I can think of, other than checking for float/metering plate interference, which I will investigate as soon as I return to my friend's shop tomorrow.

[Site Admin]

God, the only thing left is that the float is hitting the metering block when you install it.

[Jeff Kempton]

Lo and behold; I checked the float and sure enough it was hanging up on the back face of the metering block. Replaced it with a late model composite float which offered more clearance than the brass one, and it seems to be working well now. I hadn't run into that before, but I sure won't forget to watch out for it in the future.

Mitch and Doug; thanks for your help.

[Mitch Bonnar]

Holy Cow ! Glad you found the resolve.