Hey to all, I am new here and this is my first post. I have a 1968 F100 with a 360, straight shift. The truck is original paint and original interior with only 58,600 miles. A true time capsule. Now for my problem. It all started when I rebuilt the original Autolite 2100 carburetor due to flooding issues. Needless to say "MY" rebuild failed for some reason because after reinstalling the flooding issue got worse. I might add that the truck before my rebuild cold started with manual choke just fine and ran like a champ. But, after sitting about 15 minutes after being ran the fuel bowl would leak down causing it to flood and be hard to start when the engine was warm. Soooo, I bought a newly reconditioned Autolite 2100 carb from Autoline out of Canada through Autozone. I have had very good luck with them in the past on other vehicles. I installed the new carb, and 8 new Motorcraft spark plugs, gaped them to .035, changed the oil out of fear of having gas in the oil due to previous flooding issues and started the engine. Started fight up, idled fine, but, when driving she bucks and jerks like it has a miss fire. Readjusted the settings on the carb to no avail. Spoke with some old head mechanics around here that said I need to swap that carb out cause I may have gotten a bad one or the fuel pump could be going bad. So I replaced the carb again,same problem. Replaced the fuel pump, didn't help. Checked the timing, it was at 12 DBTDC book says should be 6DBTDC. However I could tell BTDC seemed a little smoother so I locked it down there. Rotor cap and rotor button are good. I pulled a vacum on the distributor and the weights do advance. I am at a loss. The truck, starts fine warm or cold. Idles perfectly. But buck and jumps when driving. No tach, but seems to miss at about, just guessing here, 1500 rpm and above. 35 to 50 mph. Seems to smooth out at 60 mph and above.Advice please.

 

When 8D is typed together, you get that smilie face unless you disable smilies in text...as I just did.

 

 

 

I believe the vacuum canister is bad on the distributor. With the vacuum line hooked up to the carb I experience the problem I explained earlier. This morning I disconnected the vacuum line from the carb and advanced the timing from 8 DBTDC to 12 DBTDC With the vacuum port on the carb plugged off, I then drove about 5 miles reaching about 60 mph. The jecrking stopped completely and it ran smoothly like nothing was wrong. Does it hurt to operate it like this? My parts store is having a hard time finding an EXACT replacement for the vacuum canister.

 

C5AZ-12370-A .. Vacuum Advance (Motorcraft DD-190) / 1968 F100 360 3 M/T: Use with distributor marked: C8TF-12127-L / Obsolete

1965/67 F100/350 352 / 1968/69 F100/350 360/390 // 1965/66 Galaxie/LTD 352/390.

This was once a very common advance, should be available from NAPA, indie auto parts stores.

Give the parts store the Motorcraft part number, it can be crossed over to the brands they sell.

 

Vacuum can actually pulls in extra timing advance under certain specific conditions, mostly when cruising steady on level ground at any speed. Anytime the engine load levels off, it kicks in. V8 normally runs about 50° BTDC under those conditions.

This is a different system than the RPM driven mechanical advance. Without vacuum advance you'll likely lose a few MPG, and it also helps the engine run cooler. Retarded ignition timing can lead to a sometimes hard to diagnose overheating. Don't "have" to have vacuum advance but any street driven car or truck will benefit.

Don't worry about the timing on the front end, somewhere between 10° and 20° is fine, spool it up and see where it stops advancing on the far end at the damper/balancer, that's what counts. Once you get close to 20° initial it would gradually get harder to crank, with starter kickback. But the initial timing isn't critical.

About 34° BTDC or so is what you want to see with pump gas around 3000 RPM or less. Make sure it's done advancing all the way. Keep advancing the distributor in small amounts till it pings under hard full throttle acceleration and back off a bit.

THEN, when you find a vacuum canister, install it, hook up the vacuum line back up, but Don't **** with, don't touch, the distributor timing anymore. The vacuum cans are adjustable with a 3/32" Allen wrench, tailor the amount of vacuum advance till it runs good in part throttle acceleration. This can be tricky because

A. It can't really be measured easily, unless you can talk your buddy into riding in the engine bay with a timing light while you cruise down the highway. If you were to rev up the motor in neutral with the vacuum advance connected it will show an inaccurate number, because there is no load in the engine. Load is really low at highway cruise, but there is still some.

B. The vacuum cans are generally adjustable for "when" but not "how much" advance so they can be touchy. They can pull in too much on the far end, you may have to limit this with a stop. Again, don't mess with the initial or mechanical advance to compensate for too much vacuum advance getting pulled in. As you're starting to guess this can be a PITA setting up a distributor but it only needs done once and you'll thank yourself every time you drive it. It is the heart of any engine.

 

Excellent advice. I appreciate your input immensely and will do as you instructed. Thanks so much.

 

Also, thanks to "Numberdummy" for the part # info and the correct part terminology. Helps a lot!!!