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I recently “finished” (haha!) a 1967 F100 project, and I am now, for the first time, able to properly drive my truck. Although it is on the one hand great and wonderful, on the other hand, an issue has arisen.
My setup is a ‘67 F100, with a FE360 from 1975, with a standard Motorcraft 2-barrel carburetor. She starts fine, and has lille-to-no unwanted noises. When the engine is warmed up, it idles great. However, when I put it in gear and start driving, it almost sounds like it’s running on 6 or 7 cylinders. It feels weak. Sometimes after I accelerate “hard”, it will backfire for a second or two.
Your plug looks good.
Here are some suggestions-
Did you run a compression test? I would start with this.
Is you vacuum distributor advance working? (suck on the hose going to it and see if the engine speed increases)
Is the hose connected to the right port on the carburetor?
I see a temperature controlled vacuum valve which is likely connected to your distributor. These often fail. I suggest you install a vacuum gauge on the line going to the distributor when the engine is hot, put the truck in gear, foot on the brake and accelerate to about 1500 RPM. The vacuum should go up going to the distributor or the valve may be defective. You can bypass it to see if it helps.
Did you have the vacuum line disconnected and plugged when you set the ignition timing?
Does the timing jump all over the place when you try to set it?
Is you plug wiring in the correct order and securely plugged in on the plugs and the cap?
How old is the coil?
A worthwhile future investment may be to convert the points and condenser to electronic by installing a conversion kit for about $100.
Engine compartment looks clean. You did a nice job.
You're lean...probably a vacuum leak. I second the others recommendations. Also, if it's an automatic, the vacuum modulator valve could be bad or the vacuum line going to is leaking.
You're lean...probably a vacuum leak. I second the others recommendations. Also, if it's an automatic, the vacuum modulator valve could be bad or the vacuum line going to is leaking.
Thanks for all those suggestions, I will go through all those things and we’ll see . I’ll report back!
After spending 2 hours reading the history of your restoration in another link I am very interested in hearing how you fix this.
Your fabrication skills to restore the cab on the truck were impressive.
Restored a 69 Mustang including the rebuild of the FE 390 with my son a few years ago.
After spending 2 hours reading the history of your restoration in another link I am very interested in hearing how you fix this.
Your fabrication skills to restore the cab on the truck were impressive.
Restored a 69 Mustang including the rebuild of the FE 390 with my son a few years ago.
Ok, so far I found and plugged one small vacuum leak, and confirmed initial timing at 10 degrees. I have checked and confirmed both mechanical and vacuum advance, they seem to work fine. Firing order confirmed correct. I unscrewed all the plugs, and they all look like the above picture, except plug number 4, which is black and sooty. I was going to check compression, but alas, my tester broke, so I will go get a new one today. I suspect however, that the compression will be down in number 4...
no compression (or close to none) in cylinder 1, 3, 4 and 8
about 120 psi in 2, 5, 6 and 7
...I'm surprised it runs at all...
Any suggestions? The truck was parked in 1998, and basically hasn't been started since then, until I started it up a couple of months ago. I took the valve covers off to verify that everything moves, which it does.
So, I put pressure in the cylinders with bad compression, but can’t hear anything leaking out the carburetor or exhaust, which makes me think it’s rings possibly… I added some miracle fluid to the oil, so I will now wait and see if that helps I guess…
In my 70 f250, I let the 390 sit for 20 years. It was a newly rebuilt engine. It always had low vacuum pressure. After driving it like that for 5 years(about 6000 miles), I put the rebuilt 360 in it that was supposed to go in my 72 f250 4x4. I pulled the heads off the 390 and all the intake valves leaked. I ended up lapping all the valves and sealing them up and then put it back together, The engine is in the 4x4 now and I am about ready to fire it up. If you didnt go through the motor, it might have more than one issue.
Check to see all intake and all exhaust rockers move about the same amount to verify you do not have a cam with one or more bad lobes.
If you expect blow by the rings, take off the oil filler cap when you pressurize the cylinder and you should hear it. I typically put in about 100 PSI to hold the valves closed if I need to change the valve stem seals.
Put about an ounce of 10W oil in the cylinders with the low compression if it does not improve after you let it soak. If the compression does not come back up, you may have burned valves. Someone may have overheated it. You will not know if lapping the valves will help until you take it apart.
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. I’ll report back!
