HudginJ3 wrote:

TKOPerformance wrote:

AEM gauges are typically very reliable and accurate.  Where is the sensor located?

So I understand this fuel system correctly: there is an electric pump feeding the mechanical pump which then feeds the carb, correct? 

 
The sensor is located aft of the short header coupling on the right side at about a 45º angle. 


Your are correct on the fuel pump set up. I have an on off switch on it also. I installed to prime the fill the carb bowls because they dry up after letting it sit for weeks at a time before starting it again. The more I think about it, it has to be the fuel pick up sock. Right now I'm swamped with airplanes so it is sitting till I can get to it.

Do you run electric pump continuously to feed mechanical pump?

I talked to the guy at Mr Carburetor here in town. He said he never heard of a carb running out of gas with a 3/8 line. But it may be possible that I need a hi-flow fuel pump not hi pressure. They are usually used on cars with nitrous.

It is inline with no check valve or bypass in the system. The electric fuel pump an Edelbrock and so is the carb. It's a 6.5 psi, 120 gph spec pump. It's not very old. I need to check the pressure on it also when I get to it. I've read about problems with them. 

HudginJ3 wrote:

I talked to the guy at Mr Carburetor here in town. He said he never heard of a carb running out of gas with a 3/8 line. But it may be possible that I need a hi-flow fuel pump not hi pressure. They are usually used on cars with nitrous.

But the fuel line isn't really 3/8" its 5/16".  You go by ID not OD.  It seems trivial, but another 1/16" in diameter is an increase of almost 70% in volume.  The problem with carbs and fuel line size is that they have to move a high volume of fuel to make power because it can only move at very low PSI and not blow the needle off the seat.  EFI by contrast is moving fuel at 40+PSI, so a 5/16" line is adequate to make 550HP.  At 4-6psi it supports MUCH less. 

Anyway, a bit academic at this point.  I'd still verify that the pickup sock, etc. is okay and that the pump can support the engine before changing out all the fuel line. 
 

Last edited by TKOPerformance (8/02/2021 5:20 PM)

TKOPerformance wrote:

HudginJ3 wrote:

I talked to the guy at Mr Carburetor here in town. He said he never heard of a carb running out of gas with a 3/8 line. But it may be possible that I need a hi-flow fuel pump not hi pressure. They are usually used on cars with nitrous.

But the fuel line isn't really 3/8" its 5/16".  You go by ID not OD.  It seems trivial, but another 1/16" in diameter is an increase of almost 70% in volume.  The problem with carbs and fuel line size is that they have to move a high volume of fuel to make power because it can only move at very low PSI and not blow the needle off the seat.  EFI by contrast is moving fuel at 40+PSI, so a 5/16" line is adequate to make 550HP.  At 4-6psi it supports MUCH less. 

Anyway, a bit academic at this point.  I'd still verify that the pickup sock, etc. is okay and that the pump can support the engine before changing out all the fuel line. 
 

 
The only problem is 3/8 ID tubing is 1/2 OD. The fittings will need reducers on the connections to get it installed. It seems logical to me that the sock is messed up. But won't know till I check it.

NOS681  Yes it did run out of gas before the electric fuel pump install. I always figured it was a not good mech pump. A new one didn't fix it. I actually need to check the pressure of both pumps and the sock. The sock is original to the car.

TKOPerformance wrote:

When you step up to 3/8" fuel line you have to change everything so there are no reducers.  The fuel pickup in the tank, the pump, etc. all must have 3/8" inlets and outlets or there's not much point. 

Exactly. So where do you get all those components? They don't exist, probably, unless you go to full race components. I guess a guy could drill and tap for the fittings needed.

I got the fuel pick up probe removed. It wasn't plugged up in the least bit. Matter of fact the sock wasn't even on the pick up tube. I had to drain the tank through the pick up tube and while doing that the fuel stopped flowing. I thought the tank was empty and thought better. I blew in the tank and it started to drain again. It took several time of doing that till it stopped completely. I proceeded to remove the pick up and got gas all over the place even though I was prepared for it. The sock was in the tank in complete condition so I made a scoop out of a spare piece of aluminum and scooped it out. When I touched it the plastic screen it disintegrated. I think I found the problem.            FYI  The electric fuel pump puts out 6.5 psi.

Good news, sounds like this will resolve your problem.  Keep us updated when you get it back on the road.

Well changing the fuel pick up did nothing for it. In overdrive and fourth all is OK, shifting into third and flooring it at 65 mph it starts to go then runs out of gas. I held it floored till it got down to 40 mph, as soon as I let up off the throttle it took off. As long as I keep my foot out of it it runs fine, but not if I fly low.

Did you try blowing air through the body hard line in both directions after finding the bad sock in tank?

Perhaps stuff might have migrated into the hard line?

I would suggest running without electric pump the way you described the plumbing.

If pressure output is good on mechanical pump, I would go through the carb and ignition system again.

On the electrical side, I would check the following as it is common to all cylinders:

( Not in any particular order, just to verify.)

1) ignition wiring…including the ignition switch, firewall connector, both interior and engine side wiring

2) distributor wire to coil

3) coil…I know that was replaced too

4) ignition module…I have read about the lead free solder having cold solder joints

5) battery…doubt it according to previous info


I was able to reuse all my gaskets on my Eddy 1406 carb and it is over 20 years old.  I had varnish in bowl that plugged up passages intermittently.

I sure hope ya find the gremlin causing the problem.

Bolted to Floor wrote:

Well Doug….. that’s really aggravating. I thought the sock was the problem. Will you continue to work this out or live with it for now?

I was hoping the sock was the problem, but highly doubted it.  It was in one piece till I touched it.I made a scoop out of a piece of flat aluminum and scooped it out. When I touched it, it fell into 4 pieces. So I replaced it.

NOS & TKO  I replaced everything you suggested since I installed the Duraspark system forgetting about the fuel issue. During all that I replaced the fuel line that I bought back in 2004. That's how long this has been going on.
I looked up performance fuel pumps on Summit. They are 130gph and 8 psi and more. The specs for the carb say that 6 psi is the max. Would lowering the float level take care of that?   Everything on your list has been done except replacing the hose between the fuel line and carburetor. thats the hose I connected the pressure gage to.

HudginJ3 wrote:

Well changing the fuel pick up did nothing for it. In overdrive and fourth all is OK, shifting into third and flooring it at 65 mph it starts to go then runs out of gas. I held it floored till it got down to 40 mph, as soon as I let up off the throttle it took off. As long as I keep my foot out of it it runs fine, but not if I fly low.

Kind of jumping into the middle of this but what you're describing is a classic symptom of a partially clogged fuel filter.  Do you have one in the line somewhere (maybe one of those that screws into the carb) that you can replace?

HudginJ3 wrote:

Well changing the fuel pick up did nothing for it. In overdrive and fourth all is OK, shifting into third and flooring it at 65 mph it starts to go then runs out of gas. I held it floored till it got down to 40 mph, as soon as I let up off the throttle it took off. As long as I keep my foot out of it it runs fine, but not if I fly low.

Is there any portion of the existing fuel line where there is a rubber hose?  If so, it maybe it is collapsing under a heavy load? 
Does the carburetor have a filter, or screen, installed at the inlet to the carburetor … maybe it’s partially clogged?
Check the needle & seat, maybe it is too small to provide the fuel needed under high RPM?
Consider running a temporary fuel line from the tank forward to the fuel pump, this will at least tell you if the existing fuel is causing the problem.
Consider rigging up a small (like 1 gallon) fuel tank that you can place in the engine compartment so as to eliminate the entire fuel line and tank pickup.