Carb flooding... fuel pressure?

[Calif240]

So I've got my new engine running and getting other things back together. The problem now is that I just fixed some of the leaks in my fuel lines, but now the Holley 750 double pumper actually floods fuel from the secondaries. I've adjusted the float levels for the front to the middle of the window. The rear will not adjust down no matter how much I adjust the needle/float adjustment. The fuel is way over the sight level. However, the front and rear bowls are supplied from the same line. I pulled the needle assembly and no dirt or obstruction. I'm wondering if because the front line comes off at 90 degrees, it is getting slightly less fuel pressure and the rear is getting more. I'm running a Holley mechanical fuel pump that advertises 110 GPH and 6-8 PSI. I don't run a return line. Wondering what the issue could be with the carb or fuel pressure... any ideas? I was told that the fuel pressure shouldn't be a problem since it at most 8PSI and more likely 6-6.5. Fuel pressure regulator needed? Return line needed?

Any experience or suggestions are greatly appreciated...

Thanks,
Terry

[cudaken]

Tap the rear bowl with a hammer? I am not kidding, has worked of me. 

[BSB67]

Tap the rear bowl with a hammer? I am not kidding, has worked of me. 

I too would guess that there is still something hanging up the float/needle or sealing issue.

[Dino]

Sounds like the floats are stuck.  Time for a mini rebuild!

[firefighter3931]

Sure sounds like the rear float is hung up....check the needle & seat for debris. 


Ron

[ACUDANUT]

8 psi is too much for a Holley. They will overflow and fuel will come out at the top of carb.  I would get a fuel pressure control valve and bring it down 1-2 psi.

[BSB67]

I have never seen a std. Holley pump overrun a properly functioning Holley carb.  Those pumps are on nearly every muscle car out there without running a pressure regulator without an issue.

[ACUDANUT]

True, but had a electric fuel pump that produced 8psi and I had tune it down on my holley.

[Calif240]

Yeah... looks like it might have just been float levels and just a small amount of debris. I re-cleaned and couldn't find anything. However, I think because of all the excess fuel, the plugs are fouled now. She won't fire even though nothing else has changed. I pulled a plug and it was dripping with gas. So have to get a new set of plugs now. Hopefully with all the floats set back correctly and needle and seat cleaned, she'll fire up with the new plugs.

Let me know if I should do anything else when changing the plugs. I'm using NGK V-power XR5's. I want to be sure any residue is gone and that any gas that washed oil off the cylinder walls is gone and that the walls are good for startup. This is a new engine and going through break-in.

Thanks,
Terry

[69wannabe]

I have always liked the carter street fuel pump over the holley pumps. The holley pumps tend to have too much pressure and the carter is 6.5psi max pressure. I have ran these pumps with edelbrock and holley carbs with no problems. Mancini Racing still sells them and the part number is a 6903 I think. I think Ron likes these pumps also.

[RallyeMike]

Since only one bowl if flooding, it's unlikely to be going to be fuel pump pressure. I'm not sure how much fuel you pumped through it, but check you oil for gas smell before you fire her up.

[Calif240]

Just an update. Cleaning everything a second time and doing a readjustment of floats seemed to have helped. I had fouled the plugs bad, so got some new NGKs and she fires up. Oddly enough though, the new fuel pressure gauge shows a steady 9 psi from my mechanical holley pump that is rated at 6.5-8psi. Carb runs good now though... Thanks as always guys.

Terry

[firefighter3931]

That's good news Terry....keep an eye on that fuel pressure and if the same thing happens again you will have to consider a new pump or a regulator for the current pump. If that 9psi reading is accurate it will be or become a problem. 

It's allways possible that the guage is inaccurate as well. The fluid filled guages are notorious for being off once they get heat soaked. 


Ron