Fuel delivery problem - I'm stumped - FFCars.com : Factory Five Racing Discussion Forum

dallas_ · 09-23-2012, 12:42 AM

ok, here is my problem, I stopped getting fuel pressure to the carbs.

This is the 2nd time this has happened. When I installed the fuel system I was getting a solid 3psi to the fuel pressure gauge. After a few go cart runs the pressure dropped to 0. Car would barely run.

I disconnected the supply line and blew it out back to the tank and reconnected everything to see if it was getting an air lock. System pressured back up and worked for a couple of days. Then the same thing happened again.

Redid all the supply lines and replaced the fuel pump. (external electric pump).

Worked fine and thought the problem was solved but the exact problem recurred today.

Here is my setup: Fuel Safe fuel cell, -8 line, 100 micron filter, Holley black electric pump, 10 micron filter, Weber carbs, Mallory fuel regulator, -6 return line.

Any ideas???

Thanks,
John

Gordon Levy · 09-23-2012, 12:46 AM

Check your first filter. There is a powder preservative in the fuel cell that will plug filters when new.

rich grsc · 09-23-2012, 12:58 AM

Do not put a filter on the suction side of the pump, not needed!!

2FAST4U · 09-23-2012, 01:04 AM

Is the pump located below the pickup?

dallas_ · 09-23-2012, 01:07 AM

Quote:

Originally Posted by 2FAST4U

Is the pump located below the pickup?

Well, it is lower than the top of the tank but not below the bottom of the tank. There is a pickup line that runs inside the tank to the fitting at the top of the tank, then my supply line runs down to the pump. The pump inlet is about halfway between the top and bottom of the tank.

Mike Brasfield · 09-23-2012, 01:51 AM

3 psi seems too low. I would set it about 6-7psi.

tirod · 09-23-2012, 01:55 AM

You should only have a fuel sock inside on the pickup. The pump should siphon, but electric pumps don't have nearly as much as a mechanical. They need to be close.

Describe what kind of -8 line is being used, and the specific SAE rating it was labeled. Was it the same kind that replaced the first used? How much - running length?

dallas_ · 09-23-2012, 02:02 AM

Quote:

Originally Posted by Gordon Levy

Check your first filter. There is a powder preservative in the fuel cell that will plug filters when new.

Thanks Gordon. I'll try that.

Quote:

Describe what kind of -8 line is being used, and the specific SAE rating it was labeled. Was it the same kind that replaced the first used? How much - running length?

Aeroquip teflon line. The fuel pump is right behind the tank so the total length of line from the tank to the pump is maybe 2'.

I pressure tested the lines and fittings to make sure I wasn't sucking air between the tank and pump.

Quote:

3 psi seems too low. I would set it about 6-7psi.

Webers don't like it much over 3 psi. I have 0 now, can't even get it up to 3 much less 6-7.

2FAST4U · 09-23-2012, 02:54 AM

What fuel pump do you have?

dallas_ · 09-23-2012, 03:46 AM

First pump was a Holley 125 HP, replaced it with a Holley black.

TXBLU · 09-23-2012, 04:00 AM

It kinda sounds like you might have a filter problem. Do you have a 100 micron filter betweeen the tank and the pump, with a 10 micron filter between the pump and the carbs? I always thought you should have the 10 micron filter before the pump, and the 100 after. A little bit of junk from the tank would clog the 100 pretty quick.

By the way, what are the pressure ratings for the pump and regulator?

Eric

tomh440 · 09-23-2012, 04:00 AM

Is the tank or cap vented? Could you be getting a vacuum in the tank after it runs for awhile and pulling out the gas? Loosen the cap and see if it helps.

TXBLU · 09-23-2012, 04:02 AM

Quote:

Originally Posted by tomh440

Is the tank or cap vented? Could you be getting a vacuum in the tank after it runs for awhile and pulling out the gas? Loosen the cap and see if it helps.

Dang, I wish I'd thought of that! That soulds like a likely cause.

Eric

dallas_ · 09-23-2012, 01:51 PM

Quote:

Originally Posted by tomh440

Is the tank or cap vented? Could you be getting a vacuum in the tank after it runs for awhile and pulling out the gas? Loosen the cap and see if it helps.

Good idea. I'll check that again.

pefflyem · 09-23-2012, 04:22 PM

The Fuel Safe fuel cell has a vent fitting on the top with a roll over check valve which vents the tank. This fitting should have a vent hose attached to it with a big loop in it and routed to a point higher than the fill hose to prevent fuel spills. Make sure the vent hose is not blocked.

dallas_ · 09-23-2012, 05:15 PM

Quote:

Originally Posted by Gordon Levy

Check your first filter. There is a powder preservative in the fuel cell that will plug filters when new.

The first filter was ok but the 2nd filter is clogged. I'll switch that out and see what happens.

Pefflym, I checked that and it's all good.

Thanks for all the input guys!

Jim Doak · 09-24-2012, 03:03 AM

Your problem may be that you're not siphoning like you should. (Pump may not be mounted low enough.)

From the instructions for the Holley black fuel pump:

The inlet and outlet of the pump must be mounted below the lowest point of the tank. This is necessary to allow for an adequate fuel supply. The pump is designed to push fuel and not designed to suck fuel out of the tank. It needs to be gravity-fed or if it’s pulling from the top of the tank, it needs to develop a siphon feed to the pump.

UrQ · 09-24-2012, 12:03 PM

I see you have a Fuel Safe cell, I just hit an issue that took me a race season to figure out (as I was also stumped), as Fuel Safe uses a flex line from the plastic line to the AN fitting at the top of the cell, this line is should be replaced every 1-2 years as it will deteriorate and cause lack of fuel pressure, I was down to zero at the last race. I had the cell apart at the start of the race season to check the filter (sock) and did not notice this issue, if I had it would have solved my fuel pressure issue.
Also make sure that the collection box at the end of the pump is working correctly and not allowing fuel to leak out during a turn or braking conditions as that will also cause low fuel pressure

The line was in decay from the inside out and from the outside in

tirod · 09-24-2012, 02:38 PM

Well, gee, the OP had responded he used teflon fuel line, so I put the monkey and organ back in the closet.

Briefly, all the old spec hose, including AN, deteriorates when exposed to alcohol and additive laced modern fuel. The new teflonized low vapor stuff won't. It's a problem that will eventually correct itself, unfortunately, some have had catastrophic loss discovering it.

The evidence suggests that even the professional suppliers aren't up to speed on this issue, they are shipping products with hose that can potentially go bad. You all need to protect yourself against business as usual.

dallas_ · 09-25-2012, 09:51 PM

Dang. I changed out both filters and still have the problem.

I'm going to pull the Fuel Cell out tomorrow and troubleshoot the whole system to see what the problem is.

UrQ, I saw your post on that and see that part on the fuel pump that came with my tank. I'm running an external pump so I don't have that section of hose in my tank anymore. Bet that was tough to track down.

dallas_ · 09-28-2012, 02:28 PM

Found the problem. The pickup line was a little too long which caused it to curl up a bit at the bottom. Even though there was almost 5 gallons of gas in the tank it was sucking air. So basically I was out of gas.

Thanks all for the ideas and input. I appreciate it.

On to inspection today, then hopefully title and registration.