I'm having a fuel pressure issue after being on track for a few laps. It seems like the float bowls are being sucked dry....

Current pump is a Carter I believe the model to be 4060. This shows to be a 50 GPH pump. The car has 46 IDA webers is 2.5 litre high compression. ...also have a 2.8 that I run sometimes.

I would think 50gph would be enough so maybe something else is going on? Anyone have any thoughts?

it sure seems like that pump should be more than adequate..

any chance the ground wire is loose, maybe its cutting in and out?

I had a similar problem 2 years ago.. and never really found it
I replaced both of my fuel pumps
I had my carbs rebuilt (once by ourselves, and then the problem persisted... so once again by a pro)
I replaced 18x Stainless fuel lines with 36 x AN ends.

the problem went away
but I still don't know which thing fixed it.
and we basically replaced the entire fuel system trying to find it, over an entire race season.....

it was really frustrating to have the car cut out after 2 laps into a race
weekend after weekend...

[quote name='brant' date='Jul 1 2021, 12:25 PM' post='2927751']
it sure seems like that pump should be more than adequate..

any chance the ground wire is loose, maybe its cutting in and out?

Anything is possible. I don't think that is the case though. I too replaced the entire fuel system recently... I eliminated the surge tank and dual pumps and simply went to one pump pulling straight from the fuel cell.

I installed a dash mount fuel pressure gauge and I can see the drops. The fuel lines are wrapped to help keep fuel cool. Pump around system with PMO bypass regulator etc.

I'm at a bit of a loss. -Car is down for a repaint and a gearbox refresh. ...I'll have a look at the wiring and likely switch to one of the holley pumps I have around here and do some testing once the car is back together and see if 100gph pump eliminates the problem but I find it hard to believe that I'm exceeding the capacity of the carter 50GPH pump.

I know the Holley's are rebuildable.
I rebuilt mine when I was chasing problems... but then ended up buying brand new ones anyways... when rebuilding didn't fix my problem

not sure if the Carter is rebuildable... but worth checking.

it may have a course screen (filter screen) inside of it.
the Holley's do..
again...just in case its plugged (not too likely)


the 50gallons must be emptying your cell 5 times over every hour..
has to be adequate... as you are most likely burning around 5 gallons in a 20 minute session...

is it possible that without the surge...
that your sucking enough air in the corners, to cause the bowls to run low?

maybe fill the cell to the brim and see if the problem continues?

also check your pickup inside of the cell for a pin hole leak?
or a fitting leak in the cell... that could break the suction..
(is your replacement single pump low/below the cell?)

sorry.. grasping at straws
brant

Brant would know far better than I would. But first thing that I think of is - when did this start happening? Always been an issue or is it a recent occurrence? Only in turns or straights too?

I know that some folks have added baffles to their IDAs to control starvation in some cases. But you are seeing the pressure drop before the carbs, right?

You mentioned removing the surge tank. If this just started happening, I would echo brant's sentiment about the surge being necessary to keep the bowls full.

Brant's mention of the coarse fuel screen reminds me of another case. I was racing at Daytona in a real hot Mustang. We were topping out consistently at 162 and that was because of the short rear end gear (banging off the rev limiter at the s/f line). All of a sudden our top speed started dropping lap after lap. Couldn't figure it out till I suggested opening up the fuel cell and checking the pump. Sure enough, the fuel cans they were filling from were leaving rust particles fuel which then plugged up the sock in the tank, but only fully under long stretches of full throttle. By the time I downshifted for T1 and sloshed the fuel around in the infield, it ran great. But when we got back up on the banks at full throttle, the sock would plug up again.

Might be worth checking all your fuel screens/socks and filter again.

I'm betting on a screen somewhere in your system is clogged...I had repeated issues with fuel cell debris clogging the Earls inline filter...went to a larger Aeroquip...look carefully...

Thanks all. I'm going to put some effort in later in the month. I'll try to report back my findings.

I was having a similar issue on my vintage 911 racecar. The motor at the time was a 3.5L with a little over 300 hp. A few things to consider:
- You can measure fuel volume "in situ" by disconnecting your main fuel line to the carbs, or the return line if you have one, and make sure you're actually getting 50 gph. This would help rule out a clogged strainer, filter, etc.
- 50 gph should be adequate, but you never know. I had a pump on my car that put out like 80 gph and somehow it was insufficient. I switched to a Holley and problem gone.
- Consider the possibility of a fuel pickup issue in the tank/cell. On a carbed car a tank pickup issue can be harder to trace because the fuel is in the float bowls can mask momentary pressure fuel pressure drops. It will catch up with you of course after a few laps, which is similar to what you are seeing. I had this problem on my car as well. Turned out to be a restrictive fuel strainer before the fuel pump in my car.

You mention a fuel pressure issue. Are you measuring fuel pressure? On a carbed car you might see it on a pressure gauge a few seconds before you the float bowls drain and actually starve.

What about fuel sloshing in the tank? Maybe add baffles or foam to the tank? Is there an old fuel return line in use, maybe that needs to be turned down or off. I know I have one in use from the factory injection system.

Also if your fuel pump is only 3.5 psi and mounted at the tank, it would be better to get a higher pressure like 4-6 psi and regulate it down at the carbs. There is pressure loss as the fuel flows.

Not slosh. Tank full. Fuel system has a bypass regulator with return line. …not a 3.5 pump.

Going to double check pick up and search for air leaks/cavitation issues. …or may simply put bigger pump on and possibly add Holley fuel mat to bottom of cell

Do some research on the fuel mats. I considered using one, but heard mixed reviews on how well they work. Curious to hear if anyone here has used one with success.

FWIW the most recent of several fueling issues I've had was an intermittent wiring connection to the pump, which took a while to find. The symptom was similar ie everything fine then suddenly no fuel, then fine again.

I've been running the Holley Red pump which is rated 97gph with a 2.7/Weber46 engine and no volume probs whatsoever. Also have the PMS/FuelSafe cell which works well in terms of sloshing and pickup. Two filters, large one near the pump and small inline one just before the carbs.

Previously I have also had clogged jet issues which are no fun either, but nowhere near as bad as total fuel cutout.