'78 F-250 460 with Edelbrock 750. When I really get on the accelerator, particularly when it is hot and towing. It bogs down kind of like it is running out of gas. I've noticed this happens more readily when we are having some of the hot temps we've had the last part of summer (close to 100 deg).

I have a friend who has a 67 caddie he is working on. He has discovered his runs bad in the heat. He was told it is becuase these older engines aren't designed to run on this gas mixed with alcohol we have today (especially the cheap 85 stuff). The alcohol is evporating faster when the carb is hot, causing a different combustion of the fuel. It was recommended to get a insulating spacer for his carb and to actually use the higher octane fuel. Could this be the source of my problem?

Another theory I have, is that I have read the 750 Eddie needs less fuel than many fuel pumps put in and need a fuel pressure regulator. Could I be actually flooding it and need the regulator?

 

^All are possibilities. You also might want to research timing and distributor curves.

 

What rods, jets and springs do you have in there? Have you checked choke and float settings? How is your accelerator pump set?

 

I've already done distributor and timing, fuel pump and filters. That was my first culprit when I started having this problem.

The problem is we are about to have cooler weather (the high today is 20 degrees cooler than yesterday;86-66), so I don't know if I am going to diagnose this very well until next year.

 

Psychlo- that was way more technical than my experience.

 

It's really not all that complicated.
Good things to know
Edelbrock.com - Tech Center - Carburetor Installation and Tech Videos

 

how much pressure are you getting on the feed line to the carb?

 

Just a thought have you checked your plugs and plug wires and ignition coil output? Electrical resistance will increase with heat so you may not be getting enough fire to your cylinders? Just a thought, throwing out ideas, don't shoot me.

 

That's correct, Edelbrock carbs like 5-6lbs of pressure at most, anymore tends to override the needle/seat.

Stock fuel pumps typically put out between 5-8 psi, so more often than not a regulator is required.

 

This is good to know. I have Edelbrocks on both my trucks and no regulators.

 

Would that fuel pressure issue be exacerbated by hi temperatures?

 

I cant watch the video to see what it says, but everything on these carbs is pretty simple. A free copy of the manual, found here, will help tons. It's got great troubleshooting, information on how to tune it, part numbers and lots of other good information that you should know when something as iffy as a carb is metering your fuel.

I cant say for sure in your case, but in the several of these carbs that I helped friends with who had problems like you describe after a "Performance tune," of some sort, they had the pump shot set as high as they could get it in hopes of...I dunno, doing something.

They also had idle turned way fat as well, for some reason and that didnt help the situation at all. While you'll not spend much time at idle, that circuit DOES affect every other metering circuit that you use, to some extent.

Anyhow, your accelerator pump (which is what seems like it's the best place to start) is a little piston thingy that gives a squirt of fuel when you open the throttle with any speed. It's inside the carb, but the setting we're interested in can be seen just by removing your air filter; on the very top front driver's side, there's a plastic bit sticking up that's attached with a linkage to a little arm. The arm has a few holes in it and by changing which hole the linkage is attached to, you change the stroke of that piston and the amount of fuel that is squirted out; too much fuel tends to cause a hesitation that goes away after a few seconds if you were to go, say from idle to half throttle and just hold it. Try moving it to a hole that's farthest way from wherever it's set now. If it's in the middle, try setting it farthest away from the carb body, giving you the least pump shot and see how that works. I think you only have three options, so should be easy to figure out which one works best for you.

If it only gets worse, put it to the best setting and let us know; although the next steps will be to check choke and float adjustment, per page 8 of that manual.