Recently I bought an 87 F250HD, it's a non cat 460, 4v Holley 4180, and 4 spd and has 116,000 miles. I bought the truck cheap because it wasn't running well and the p.o. was disgusted with it. When I looked at it, the p.o. had the carb rebuilt, and put new wires on it. The truck ran like it had 2 wires crossed and had a strong smell of gas under the hood along with a rich smelling exhaust. When you stepped on the throttle it would back fire through the carb, note this is while the truck was parked and not driven.
When I got the truck home, I found the wires to be correct ( 15426378 firing order ).When I tried to run the engine, I found the condition had digressed to the point were the engine was running on 1 cylinder. I moved on to the carb because it appears to have been a spray paint rebuild. It appeared to have been partially dis assembled and painted gold! When I took it off I found a massive internal fuel leak in the carb. the inside of the manifold was wet with gas and 7 of the 8 plugs were wet with gas, all were black with soot.
I found the carb to be butchered a bit and bought a good core from a fellow VFM'er and rebuilt it, I used the base plate from the original carb because of some differences on the throttle lever, everything else on it appeared to be the same.
After I installed the carb, I did a quicky compression test, I found #2 to be at 180 psi, #3 to be at 130 psi and all the rest to be 150 psi. I wasn't expecting to find great results because the walls had been washed down with raw fuel. I didn't think this was too bad, I figuired the 180 psi was do to pooling of fuel in that cylinder, ( I had drained the oil and would say that there was about about 1 1/2 gallons os gas in with it! ).
I put in new plugs and started it, now at least it was running. I still had it popping through the carb though. I replaced the cheapy wires with a good set and it ran a little better. I started spraying WD40 on the vacuum lines looking for vacuum leaks because idle quality wasn't great, running a little rough, not firing evenly. Didn't really find anything.
I replaced the gasket under the carb and the one between the intake manifold and egr spacer along with the egr gasket. I checked out the egr valve with some WD40 to see if it's seat was leaking and didn't really find anything. The engine ran pretty much the same.
Next, I moved on to the vacuum lines. I disconnected the p.b. booster line and put a rubber cap on it, no difference. After that, I started to unplug the vacuum lines from the vacuum trees with caps. This helped greatly and the engine run much, much, better but still have some popping through the carb when the throttle is opened quickly and still a little roughness at idle.
With the timing set, and the vacuum line off the dist. I'm getting about 19-20 inches of vacuum with the needle fluctuating slightly.
In summing things up, at a fast idle, it seems that I have some what of a steady mis. Also I've notice that the vacuum pull off of the choke isn't really working, I need to hold the choke open with something untill the electric choke holds it open, I'm getting about 7.35 volts to the choke. I don't think I missed something when I rebuilt the carb, but it's possible, I'm not going to assume anything. I've also have taken all the plug wires off one at a time to see if it was anyone cylinder is causing the problem, but it didn't go away ( back firing through the carb ). And yes the timing chain is a little worn.
I'm getting a little frustrated because I'm missing something but can't quite figuire out what. I think I still have a vacuum leak causing the back firing and also forgot to mention the egr plate looked in very good shape. Any clues, ideas, HELP!!!!!!!!! please, thanks.
Tom
You can do anything you want to......ONCE!
aka "my 66 coupe"
