Fuel being sent out of overflow vents Holley 4150

[Lee]

Hi all. I'm wondering if anyone can suggest what is wrong. Carb? Or fuel system?

I have different pumps on either side of the car. I am using AN8 hose throughout. On left tank I have a 100 micron prefilter into a Walbro GSL392 255lph feeding into an Aeromotive regulator (which returns the the tank) and then into a non return valve. On the right tank I have a 100 micron prefilter into a Carter 4600HP 375lph (internally regulated) feeding into a non return valve. The 2 systems then go to a T then to a 6 micron filter then to the carb. 850 double pumper. Fuel pressure take off is between the T and the filter.

On the rolling road this week, no issues with the fuel while trying to sort out part throttle running from either left pump or right pump running with 6psi on the gauge, but when we tried to do power run this was happening up towards 6000rpm. It happened if only the right pump was running, and it happened if only the left pump was running. When we reduced the pressure for the left pump by adjusting the Aeromotove regulator down to 4 psi, then all was OK (but only for running on the left pump).

The same carb was used on the same engine on the engine dyno during the previous week with no such issue.

 

[Neal]

You likely have some debris in the needle/seat. Just pull the needle/seat assembly out, blow it out well, and then re-set your float level.

 

[Mark H.]

I have had very good luck with Daytona carburetor's flat needle seats . Have raced with them and never had an issue. I run LeMans bowls at 6 PSI. They seemed to make a difference as they cleaned up full throttle transition to deceleration off throttle which I attribute to a positive closing and quicker opening when back on the throttle. Not affiliated with them in anyway. https://daytonaparts.com/

 

[Devin]

Frustrating as heck…happened on my fresh built 427FE. I ended up just replacing the almost new needle/seat assembly as it happened twice. I’ve sworn off ethanol as much as possible and haven’t had an issue since then.

 

[Lee]

Thanks for feedback. Will try to find out more about Daytona float valves. Strange why it happens on BOTH primary and secondary, only at 6psi, not at 4psi, and did not happen week previously on engine dyno. Could it be anything other than both needle/seat assemblies?

 

[Mark H.]

I could see some type of reversion issue back thru the boosters on shut down that might be pressurizing the bowls but in your video it appears fuel is pushing out the vents all thru the pull. Something is amiss with your needles and seats, maybe the floats have collapsed / cracked and your levels are higher that you think due to a sinking float? You are sure the pressure is correct at the seats? Can’t see another way of pressurizing the bowls unless there is a defect, crack or other way pressure is getting to the bowls?

 

[Jean-Marc]

This could appen when one of the power valve is damaged, over pressure in the plenum is coming back in the carburator and because the throttle is close it is pressurizing the bowl ?

 

[Randy V]

Pressure gauge suspect?
How is your float level setting?

 

[Howard Jones]

Take the needle seats out of the carb and inspect the o rings. Fuel can bypass the needle seat if they are hard and flat. They get like this after about 6 months of non use. This happens ALL THE TIME to seldom driven Holley type carbs. You can buy them by the bag full like I do and replace them offen. If you use the reuseable gasket sets and measure the float levels after you have the bowls off and before you remove the needle/seats and reset to the same levels after you reassemble them it gets pretty quick and easy.

I'll look for the o ring sorce and post it here.

Holley NEEDLE and SEAT O RING - Allstate Carburetor

Holley Needle and seat o ring, Viton O-ring for Holley, Demon Needle and seat o-ring, Quick Fuel Needle and seat o-ring, O-ring for Needle and Seat

allcarbs.com

 

[Bill Kearley]

Water logged floats ?

 

[Lee]

I will check the floats and replace the needle seat assemblies, then keep an eye on the o-rings. Still don't really understand why both float bowls should show the exact same problem, only at high power/revs. But hopefully replacement needle/seats will sort it out. Thanks all.

 

[Bill Kearley]

I haven't read the entire thread but have you checked the fuel pressure with a known good gauge ?

 

[Doug Dyar]

Take the needle seats out of the carb and inspect the o rings. Fuel can bypass the needle seat if they are hard and flat. They get like this after about 6 months of non use. This happens ALL THE TIME to seldom driven Holley type carbs. You can buy them by the bag full like I do and replace them offen. If you use the reuseable gasket sets and measure the float levels after you have the bowls off and before you remove the needle/seats and reset to the same levels after you reassemble them it get pretty quick and easy.

I'll look for the o ring sorce and post it here.

Holley NEEDLE and SEAT O RING - Allstate Carburetor

Holley Needle and seat o ring, Viton O-ring for Holley, Demon Needle and seat o-ring, Quick Fuel Needle and seat o-ring, O-ring for Needle and Seat

allcarbs.com

+1 for replacing the needle and seat o-rings.

I've been chasing a recurring flooding issue on a Holley on one of my other cars. It seemed like it was related to the float levels, but repeated adjustments deteriorated over time, and the problem returned. I checked and rechecked all the adjustments. Replaced the power valve. Checked the floats for possibly taking on fuel. Nothing.

After much head scratching, it turns out that these o-rings had hardened and deteriorated, letting fuel into the bowls and flooding out the engine.

This was on a brand new Holley that was 7 years old, but unused. Fortunately a friend with decades of Holley tuning experience stepped in and found the issue.