Got this truck two years ago. Had been garaged for quite some time. Changed stuff as it broke. Then I changed the intake to edelbrock performer and put holley 4 bbl vac sec on. No egr stuff, no smog. The truck starts and has adequate power occasionally if the gas pedal is played just right. Wondering if I can get some ideas bounced on around. Timing is one ive heard but there's so many different suggestions on what it should be at. Also have heard firing order which I know I've checked b4 just changing wires but you never know. What diagnostics could I do to find out where the problem is?

 

Start by getting a timing light and vacuum gauge. Check the timing, and bring it in spec or a little hotter, as you are feeding it more with the Holley. Check for vacuum leaks, as they tend to cause lack of power and bad idle.

Perhaps consider swapping to a cam designed for 4bbl applications. Also, you should check your throttle cable for binding or stretching.

Can you give us a bit more info on the drivetrain? The gearing or transmission might be causing a feeling of power being lacking.

 

What size holley? A 750 would be too big.

Agree with RL250. Check timing and set it 10-14° BTDC at idle with the vacuum line off. Once that's taken care of and you've made sure there's no vacuum leaks you can then tune the carb.

 

A 5.0 in a truck is not going to perform like the same engine in a mustang. And many of the f100's had 2.xx something rearend ratios.

 

I'm going by the "play with the gas pedal" part that something's amiss in the setup.

The secondaries could be coming in too fast. For a truck they should be the heaviest spring IMO. Also, if it's a 750 that could be part of the problem too. Rule out ignition timing first, then look for carburetor adjustment and fuel issues.

Was it a new carb or used? If used was it rebuilt by someone who knows what they're doing?

 

The carb is a 600 cfm bought new. Not sure about transmission or gears. Most likely stock and the transmission is auto. I've put a gauge on it before and maxed out the vacuum at about 16. Wasn't sure if that's low or not for this set up.

As far as leaks, no obvious ones but I may just get a bunch of line and replace em all.

The throttle cable is about as straight as I can get it. I'm bending the original bracket cuz it's neat to have on top of all of the new stuff but I may try a lokar or mr gasket one soon just rule it out.

Cam job as been thought about but wouldn't know where to begin on buying one that would give the most for my setup. Gears seams like a more sure thing as far as knowing that I'm getting what I need

A heavier spring in the vac secondary. That slows the opening of the blades? Is there a way to check this? I've heard of something with a paperclip on the linkage and if it moves or something. Not sure.

Also to go more detail. It's really all low end that I'm missing. I don't have the rpm tach setup but up to about 3000 I feel like I'm pulling a trailer, a heavy trailer. But once I get the rpms up and get the transmission to do what I want the truck gets up and goes pretty good. Also I do not have kickdown back in. Doesn't reach and haven't taken to time to find a solution. When I want to pass I floor it and half the time the trans downshifts anyhow or maybe it's secondaries opening?

 

I haven't worked on many automatics but isn't that kickdown cable pretty necessary or you're going to burn out your trans? I could be wrong as my truck is a manual and never had to worry about it.

 

I had a 302 in my '80 F100 with a C4 trans and 2.75 gears, it couldn't get out of it's own way. My '92 has an EFI 302, 5 speed and 3.55 gears, what a world of difference. It has enough gearing for pretty decent get-up and go and will run 100 on the highway with ease (could do more if it weren't for the speed limiter). I'm all about power though, my '92 is getting a 347 stroker and the '80 is getting a 427w stroker. If you don't wanna go that route, I highly suggest you get at least some 3.50's in there.

 

Look on the door tag and give us the axle code. That will us the rearend ratio. That sounds like your problem. You can pull it down manually into 2nd gear and see what it does. You have to have airflow for the carb to open up, that's how it works. If you can't get the rpms up, there will be no airflow, and the carb will be waiting on the engine to open the secondaries.

 

Okay, no door tag but diff tag says 2.75. What's an ideal gear size for 2wd on this.

 

There's the biggest part of the problem.

On stock tires, 3.55 is a good all-round ratio for town driving, with towing ability & reasonable acceleration.

3.25 gearing will reduce performance a bit, while giving better highway rpm.

But the difference between 2.75 & 3.55 is huge as far as driving/power.

 

It depends on your intended purpose. If you want a gas sipper, leave it like it is. Like was mentioned, 3.50 or 3.55 is a very common rearend that can be found in the junkyard and swapped in.

I think it was mentioned also about your kickdown linkage. If you want to keep your gas mileage where it is, getting the kickdown working will really help the situation. You can see what will happen by finding a empty stretch of road, cruise along normally, and then pull the tranny lever down to 2nd manually and nail the throttle. The engine rpms should flare up and the carb should start opening up some. If you like what happens, you need to hook the kick-down up so this happens by itself. Pulling the lever down manually is a pain, it's nice for it to do it by itself.