Engine question
Thread Starter
|
Mountain Pass
Joined: Dec 2024
Posts: 134
Likes: 6
Engine question
Hey guys, I got my 68 project. It got the 390, ran a compression test today, got about 150-160 all across with 2 cylinders around the 135. How is it for this engine?
after doing that I set my timing.. I was a bit advanced from 10 btdc so I backed it off a bit , runs pretty good but I feel I got a bit lacking power still and a little lag when I actually driving the truck when I first hit the pedal.
any help and advices will help.
also, is there an adjustment to make to get the clutch to engage a bit higher?
after doing that I set my timing.. I was a bit advanced from 10 btdc so I backed it off a bit , runs pretty good but I feel I got a bit lacking power still and a little lag when I actually driving the truck when I first hit the pedal.
any help and advices will help.
also, is there an adjustment to make to get the clutch to engage a bit higher?
Fleet Mechanic
Joined: Aug 2007
Posts: 1,834
Likes: 260
From: Piney Woods of East Texas
Those 2 low compression cylinders are hurting you on power. If you have access to a cylinder leakage gauge set, I would run it to find where the low pressure is bleeding off. Could be a broken ring on leaking valve. These old engines were pretty gutless when it came to power. The low compression (8.5:1) really hurt them. Modern 4 cylinder engines generate more power than these big v8. They do develop low end torque due to the long stroke.
You can play with the clutch rod adj some. Too loose and you want be able to fully disengage it, but will raise the petal position for feel.
You can play with the clutch rod adj some. Too loose and you want be able to fully disengage it, but will raise the petal position for feel.
Trailering
Joined: Jan 2026
Posts: 20
Likes: 15
Have you ever driven a 390 with the same rear end gear ratio that you have so you have some to compare it too? Has the carb been rebuilt if its been sitting? Maybe the jets are clogged or the accelerator pump isn't working correctly.
Hotshot
Joined: Jul 2020
Posts: 10,519
Likes: 2,654
From: Near Salt Lake City
Hey guys, I got my 68 project. It got the 390, ran a compression test today, got about 150-160 all across with 2 cylinders around the 135. How is it for this engine?
after doing that I set my timing.. I was a bit advanced from 10 btdc so I backed it off a bit , runs pretty good but I feel I got a bit lacking power still and a little lag when I actually driving the truck when I first hit the pedal.
any help and advices will help.
also, is there an adjustment to make to get the clutch to engage a bit higher?
after doing that I set my timing.. I was a bit advanced from 10 btdc so I backed it off a bit , runs pretty good but I feel I got a bit lacking power still and a little lag when I actually driving the truck when I first hit the pedal.
any help and advices will help.
also, is there an adjustment to make to get the clutch to engage a bit higher?
Means at 100 the low one at 85 is ok and 84 is not
The low one must be within 85 percent of the highest one
Yours 160 / 135 is .84375 borderline fail for a misfiring cylinder
I'd run it and live with it till she puked
Hotshot
Joined: Jul 2020
Posts: 10,519
Likes: 2,654
From: Near Salt Lake City
I would at least pull the valve covers and make sure there are no bent pushrods
Agree strongly about getting the carb working properly
We used to just throw those old ones on the I/M machine to check a few things out
If the spring on the vacuum advance gets weak, the HC's will peg 2000 and they run like puke with a bad spring
Same with the power valve, if the CO is at 10 percent yours leaks
These days might just want to overhaul the carb every few years and keep a good new power valve in there
Most important is the choke and the choke pull-off also the float level and condition of the float
What altitude are you at?
Generally, you add 2 degrees of ignition timing per thousand feet of elevation
Here in UT at 5000 feet, I run my 68 Camaro 350 at 14 degrees
Agree strongly about getting the carb working properly
We used to just throw those old ones on the I/M machine to check a few things out
If the spring on the vacuum advance gets weak, the HC's will peg 2000 and they run like puke with a bad spring
Same with the power valve, if the CO is at 10 percent yours leaks
These days might just want to overhaul the carb every few years and keep a good new power valve in there
Most important is the choke and the choke pull-off also the float level and condition of the float
What altitude are you at?
Generally, you add 2 degrees of ignition timing per thousand feet of elevation
Here in UT at 5000 feet, I run my 68 Camaro 350 at 14 degrees
Mountain Pass
Joined: Jun 2024
Posts: 113
Likes: 24
From: Springfield, Illinois
Your truck sat for a looong time, all you have is idle time on it so far. A ring could be stuck on those two cylinders.
When it's drivable put 100 miles on it with the Marvel's Mystery Oil in it, then if you feel you need to check it again and compare notes.
BTW ..10-12 degrees btdc is fine, she should run real happy around there as long as you have the carb dialed in.
When it's drivable put 100 miles on it with the Marvel's Mystery Oil in it, then if you feel you need to check it again and compare notes.
BTW ..10-12 degrees btdc is fine, she should run real happy around there as long as you have the carb dialed in.
Last edited by whitey68; Jan 30, 2026 at 02:53 PM.
Hotshot
Joined: Jul 2020
Posts: 10,519
Likes: 2,654
From: Near Salt Lake City
+1 for the Marvel Mystery Oil
You can also use a quart of trans fluid with an oil change
Unstruck a pressure relief valve in the oil pump of an old Z-28 that way
You can also use a quart of trans fluid with an oil change
Unstruck a pressure relief valve in the oil pump of an old Z-28 that way
Trending Topics
Thread Starter
|
Mountain Pass
Joined: Dec 2024
Posts: 134
Likes: 6
Thank you for all the replies. Very much appreciate it
I went ahead and ran another oil change (after fixing it, letting it idle a bunch and adjusting everything) oil looked decent. Put in 10-30 and 1 bottle of marvel to sit in those valve areas overnight. She sounds pretty good. Time to run it a bunch more when weather gets normal again…
On another topic I’m trying to get my original gauges to work. I have nothing but speedometer at the moment. Any suggestions what to look for?
I went ahead and ran another oil change (after fixing it, letting it idle a bunch and adjusting everything) oil looked decent. Put in 10-30 and 1 bottle of marvel to sit in those valve areas overnight. She sounds pretty good. Time to run it a bunch more when weather gets normal again…
On another topic I’m trying to get my original gauges to work. I have nothing but speedometer at the moment. Any suggestions what to look for?
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
3 Best / 3 Worst Parts of Modern Ford Ownership
Brett Foote
10 Amazing Upgrades That Solve Common Ford Truck Owner Headaches
Pouria Savadkouei
Every 2026 Ford Engine Explained
Brett Foote
10 Ugly Ford Trucks That We Still Kinda Love
Joe Kucinski
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Top 10 Most Expensive Ford Trucks Ever Sold on Bring a Trailer
Joe Kucinski
2027 Ford Super Duty Buyer's Guide (Every Model, Engine, & Package)
Brett Foote
Top 10 Ford Truck Tragedies
Joe Kucinski
Thread Starter
|
Mountain Pass
Joined: Dec 2024
Posts: 134
Likes: 6
Thank you for all the replies. Very much appreciate it
I went ahead and ran another oil change (after fixing it, letting it idle a bunch and adjusting everything) oil looked decent. Put in 10-30 and 1 bottle of marvel to sit in those valve areas overnight. She sounds pretty good. Time to run it a bunch more when weather gets normal again…
On another topic I’m trying to get my original gauges to work. I have nothing but speedometer at the moment. Any suggestions what to look for?
I went ahead and ran another oil change (after fixing it, letting it idle a bunch and adjusting everything) oil looked decent. Put in 10-30 and 1 bottle of marvel to sit in those valve areas overnight. She sounds pretty good. Time to run it a bunch more when weather gets normal again…
On another topic I’m trying to get my original gauges to work. I have nothing but speedometer at the moment. Any suggestions what to look for?
Fleet Mechanic
Joined: Aug 2007
Posts: 1,834
Likes: 260
From: Piney Woods of East Texas
Do you have any power to the fuse block? Lights working? Check the wiring on the ignition switch. If your has the round pins they will loosen up and get bad contact. Most convert to the newer blade style. The same things happens with most all the electrical connections on these old truck. Unplug connections and check for oxidation, clean as needed and reconnect.
Thread Starter
|
Mountain Pass
Joined: Dec 2024
Posts: 134
Likes: 6
Do you have any power to the fuse block? Lights working? Check the wiring on the ignition switch. If your has the round pins they will loosen up and get bad contact. Most convert to the newer blade style. The same things happens with most all the electrical connections on these old truck. Unplug connections and check for oxidation, clean as needed and reconnect.
Cargo Master
Joined: Dec 2015
Posts: 2,253
Likes: 345
As far as the radio goes, if its the original speaker, its probably blown. On my 70 f250, the am radio works. My dad cranked the volume up fast and it was done. Its still in there. Get to it eventually. Swapping the speaker out will be a pain.
Thread Starter
|
Mountain Pass
Joined: Dec 2024
Posts: 134
Likes: 6
hey! Yes sir, plenty of work done. It’s running better , I still have trouble with the rpms , the truck seem to run on high idle almost no matter what. It’s timed, I adjusted the carb, no vacuum leaks. Still can’t seem to idle her down.
Fleet Mechanic
Joined: Aug 2007
Posts: 1,834
Likes: 260
From: Piney Woods of East Texas
Make sure the butterflies on the carb are not binding and are fully closing. You need to remove the carb to confirm this. To set loosen the butter flies and let them self align before tightening with throttle stop full off. Also the choke idle cam can stick and hold the engine at a faster idle. If this is a automatic, check the down shift linkage for binding. I've seen it on rare occasions that it does not let the butterflies close completely. If your has the dashpot/damper on the throttle stop, you may need to back it off some.