I have an issue in my 79 f-250 4x4. I built a 460 and 4 speed combo for it. Has been in about 2 years. I thought I had it pretty well dialed in in terms of timing and carb, but now have second thoughts. Idles and revs ok, BUT the other day I borrowed a ladder from my brother and returned it to him. We got to talking trucks and I told him I had never had my new motor past about 2500 rpm. He was shocked and told me when I left to stand on it. Ok, so when I left his place I got in 3rd gear and opened it up. I hit about 3200 rpm and started hearing what sounded like a misfire. It was intermittent, not a constant noise. I let off of it and drove home. Everything worked as it should under normal driving (Under 2,200 rpm). Sorry for the long intro. So, what could it be? I did some searching and am leaning towards a lean condition under heavy load. It's an Edelbrock 1405 600cfm carb on performer intake. All stock out of the box, have had it on the truck about 10 years and never had this happen before, but like I said I'm not one to really rev my motor up. Would moving the rod on the accel pump help this to add more fuel when I am at WOT? Do I need to go up a size on my metering rods? Thanks in advance,

 

It depends on how much fuel you should need. What are your build specs? If you've never been over 2500, it may not have broken in very well.

 

It's probably lean at wide open throttle. The vacuum level will drop and the rods should come up. The accelerator pump will only help the initial throttle stab, if it keeps misfiring with the throttle open the accelerator pump isn't the problem. I run a 750 Edelbrock 1407 carb on my 460 with an unknown mild cam, so a 600 will probably need to be richened up on the top end.

This is much easier with a vacuum guage and an O2 meter. That way you can tell when the rods are going to move and see when you go lean. I can send you a copy of the Edelbrock tuning guide if you need, just PM me an email.

Tuning my engine I first calculated all the cross sectional areas of the jets and rods, then lined them up so I could methodically walk through changes...THAT DOESN'T WORK and I don't know why. The Edelbrock manual has a chart showing what to change to move richer or leaner from where you currently are and the sizes shown don't add up to my calculations but they work. So just putting in a smaller rod may not be the answer, use the chart in the manual.

 

Here's a link to the manual online:

http://www.edelbrock.com/automotive/...ers-manual.pdf

 

Thanks for the replies. I do have the manual on PDF version off their website but wasn't sure if I needed to start playing with metering rods. Will post more about the motor tonight when I get time. Thanks,

 

Just take a look at what jets and which rods you have to find your starting point on the graph.

 

Turbo, like I said the jets and rods are the stock ones that came with the carb. Guess I need to look into getting the calibration kit that comes with the different rods. Thanks for the advice guys.

 

Those jet kits don't come with lots of different sizes. I'll suggest that you first take a look and make a note of what sizes are in the carb now. Then look at the tuning graph to determine the next two richer settings and be sure that they are in the kit that you purchase. I live at 7200 feet so I needed more jets and rods than the kit came with.