When I floor it at highway speeds the truck sputters and goes very lean on the gauge. It runs awesome everywhere else and in every other situation. I've been constantly tinkering with it but I just can't get rid of it. Any help?

Here's what we're talking about:

72 Ford F100
360 V8 with rebuilt top end
Edelbrock 1406 4bbl carb (rebuilt a month ago)
Edlebrock Performer Intake
Timing set to 8* BTDC
New Harmonic Balancer
Pertronix I ignition and coil
New Champion 45 plugs gapped at 0.045"
New wires
New Cap
New Rotor
Eqquis two channel Air/fuel ratio meter
Two O2 sensors (one in each header collector)

Carb jetting is at 0.103" Secondary and 0.098" Primary with 0.070" x 0.047" metering rods. Using the orange springs, the 0.043" accelerator pump squirter nozzles, and the highest hole on the acclerator pump linkage. I have an open air cleaner that I thought was the problem, but now I don't think so.

 

Get in the Edelbrock tune up book. It has the information to fatten the big end. Also, any idea what your total advance is????

 

No, I haven't checked the total advance yet. It's an OEM rebuilt unit, but I'm assuming nothing about it at this point. I didn't realize that there were any bigger jets, but I found the list of them on Edelbrock's website. I ordered a set 2 sizes bigger (0.110") than the 0.104"s I have in there now. I was wrong in my earlier post...they are 0.104" secondary jets instead of 0.103" jets. It should make a difference.

 

I changed out the thermostat today because it had been running pretty cool even with cardboard in front of the radiator. Now it runs where it should as far as temp goes without cardboard in 26 degree weather at 80 mph. The lean drop at WOT is better and doesn't last as long but it's still there. I think that can be fixed with a bigger jet.

Unfortunately, I now have pinging from 60% throttle to WOT. This is with 8* advance and the A/F gauge reading normal to a little rich. I had this problem before when I was running as high as 14* advance. This led me to think that maybe there is something wrong with the pertronix ignition. I put a meter on the coil. This is what I get at idle: Across the terminals of the coil: 2.9V to 3.2V; Across battery terminals: about 14.6V; Negative battery terminal to positive terminal on coil: about 14.6V; Negative battery terminal to negative terminal on coil: about 8.6V. Is that difference because of the voltage drop from the coil? I'm not sure this is right. I though it was supposed to be 12V or more at the coil at idle. With the key on but the motor off, I get about 12.5V across the coil.

This is how I have the ignition wired:

Positive side: I currently have the coil power source wired through a relay that is hooked directly to the always hot side of the starter solenoid. The relay is switched by the ignition switch. The red wire of the pertronix module in the distributor is also connected to positive terminal.

Negative side: The black wire for the pertronix module and my tachometer wire are both hooked to the negative coil terminal.

Any suggestions?

 

You do the highway full throttle test while reading your fuel pressure?
Bad pump, filters or semi plugged lines?
Can't help ya on them "rod carbs" as the last one I messed with was a 64 Rambler. Holley here.

 

If it runs good at cruise, don't change the jets. It needs more fuel at low vacuum, so go to metering rods that are the same size at the top, in your case .070, but smaller tips. Around .040 should make a difference. Your effective jet size is the metering rod diameter subtracted from the actual jet size. 104-70=34, 104-47=57, 104-40=64.
When I couldn't find rods with small enough tips, I filed flats on them. Easier to get two the same that way than trying to cut them down all the way around.

 

I haven't done the full throttle test while reading fuel pressure, but I have checked the fuel pressure between idle and 3000 rpm in the driveway. Fuel pump, hoses, and filters are all new. Didn't do anything to the hardlines or the tank, but the clear-view filter doesn't have any gunk in it.

As far as the rods go, it runs good in cruise and in power mode as long as I don't open the secondaries too quickly. I can mash it to the floor at a stoplight and it take right off without a single hesitation or flutter. I can also ease into the secondaries at high speed and it'll run fine. It's just when I get into the secondaries too quickly.

 

Now I'm starting to wonder if the 0.045" plug gap is too wide. I'll add this too. I'm consistently running 7.5 to 8.5 mpg highway or city. Something's not right and I think it has to do with spark.

 

I'd be curious to take a look at the advance mechanism in the distributor to make sure it is functioning properly & not over advancing the timing.

 

Yea, I think I'm going to go pick up a dial timing light and see what I'm getting at 2500 rpm.

 

Some of these trucks have an additional fuel filter atop the fuel pump, in addition to the screw in filter to the carb. If you see a metal can, there a replaceable fuel filter inside. Take care when removing the can, they can be rusted on.

C4AZ-9365-A Fuel Filter (Motorcraft FG-1)

 

I put a new fuel pump on it back in October. Also replaced all rubber fuel hoses. Not running a filter in the carb. I have a clear-view filter between the pump and the carb. I checked fuel pressure then and got about 5.5 to 6 psi at idle and while revving. I think the 2 month old rebuilt dizzy isn't advancing right. Tomorrow evening I'll have more time to dink with it.

 

"revving" vs under load are two different fuel flow demands on the fuel pump.
Check fuel pressure nailing it at 70 mph or in passing gear a 4,000 rpm's then standing on it for 5-10 seconds to see if the bowls go dry while checking fuel pressure. If pressures good it's jetting if timing is known good.
All this testing is better with a wide band F/A ratio gauge.

 

Its not like it runs and then goes dry. It falls flat on its face as soon as I floor it. If I hold it to the floor it will eventually work its way back to stoich. I'm going richer on the secondary jets today which should take care of the problem.

I've just turned my attention to the fuel mileage question because its ridiculous at 8 mpg all the time. I know I should be able to get something better than that.

 

You mentioned that you have a new balancer in the first thread. That got me to thinking about your timing being set at 8* BTDC and the WOT problem. Is it possible the balancer itself is defective? Check the timing marks in comparison the key hole for the crank. You can do this by removing the spark plug and inserting a wire coat hanger. Then slowly bring the piston to TDC. Once it is TDC verify the 0* mark on your balancer. It sounds almost like there is an issue with the timing. With a truck I would have an advance timing curve that goes to 3200 RPM or so. All in by 2500 is pretty tight IMHO. Your total advance should be around 32-34*.