Timing or Carb.? 1968 360

[Adach47]

I am new to the antique truck world. Recently purchased a 1968 F100 with a 360. Everything ran well then it didn't. Looking for any help diagnosing what is going on. I was driving the truck and it was running smoothly then it started to backfire(through carb) and miss. I limped it home, about 5 miles, and it had periods of running normally - maybe 1/4 mile at a time. Got it home and have done the following and it has not improved anything:

1. replaced plugs and wires
2. replaced distributor cap, rotor and coil
3. replaced vacuum line
4. replaced seals in accelerator pump (was leaking just a bit)

I have not replaced vacuum diaphragm or points yet. I am baffled to what could be the problem. Currently, difficult to start and seems like it is missing badly. Any thoughts out there?

[JHof44]

Have you pulled the carb and checked the base and spacer gasket? Mine was torn and causing me to lose vacuum.

[sargentrs]

is where I'd start. Go to your local parts store and get a spray can of carb cleaner/starting fluid (50% ether). Get it running and spray around the base of the carb/spacer, the intake manifold, brake booster if you have one. If it chokes down or revs up when you spray an area, that's the source of your vacuum leak. If it happens to be around the accelerator pump cover, that's a common problem. Over time the cover gets warped and won't seal. Take a piece of 120G sandpaper and tape it to a hard flat surface or wrap it around a 2x4. Remove the acelerator pump cover and place the gasket surface on the sandpaper. Stroke the cover back and forth smoothly and gently across the sandpaper. You'll immediately see the high spots getting shiny. Keep at it till you have a good, flat sealing edge all around the cover then reinstall with a good gasket. Just snug the screws, don't torque them down too tight. Since you still have points, try replacing the condenser and resetting your points. Condensers these days are pretty poor quality.

[cep62]

Maybe the resistor wire from ign switch to the coil??
Try hooking a temporary wire to the coil POS , but beware it'll start in gear and you'll have to remove the jumper to stop it.
That bypasses the ign switch.

[farmallmta]

Since you still have points, try replacing the condenser and resetting your points. Condensers these days are pretty poor quality.

Motorcraft points and condensers is what you want. Don't buy the cheap chinese crap at autozone, advance, or o'reilly!

Points: https://www.summitracing.com/parts/mof- ... lications/
Condenser: https://www.summitracing.com/parts/mof- ... lications/

[Adach47]

Thank you for the tips. Will try these and report my results soon.

[Manny]

You got the right stuff going for you here welcome to the page. Two things have already been mentioned on my list, that is cause we got some sharp tacks around here on the old iron. Whats the points dwell and timing look like. Replace the points or maybe upgrade to petronix system (Mixed success for me here love hate). Second is the vacuum leak by you a cheap gauge and check the vacuum at idle see what you go. Fluid or a propane torch Not lit just the gas flowing will make her sweeten up when you find the leak. Don't forget possible brake booster as well leaking if power brakes. One thing maybe is if the engine is very original like bone stock it could have a nylon timing chain gear and is chipped jumped a tooth. That would be a last resort thing retarding the cam timing causing bad issues. Keep us posted and welcome one again.

[Adach47]

I tightened the screws on the accelerator pump. Presto!! Started right up and runs smoothly again. It always seems that is the simplest thing that is the problem. Thank you for all the tips.

[Manny]

I tightened the screws on the accelerator pump. Presto!! Started right up and runs smoothly again. It always seems that is the simplest thing that is the problem. Thank you for all the tips.

Save the tips for the next time. Sadly there will be a next time......

[bluef250]

Most likely timing, beside previous suggestions, check the play (side to side) on the distributor shaft.

[billdoggy734]

Most likely timing, beside previous suggestions, check the play (side to side) on the distributor shaft.

I was kind of curious about this. I assume little or no play is acceptable on the distributor rotor? I have no axial play but a few degrees of rotational play. Do people just replace the gear on the dstributor or more?

Thanks!
Billy

[bluef250]

In my case, the bushings were shot. The shaft was so loose that I could not keep points gaped properly. I updated ignition to a Duraspark II (1975/76) rather than mess around with points.

[colnago]

I also replaced everything with Duraspark, but I ran with Pertronix II for years with no problems. If you're going to replace the distributor gear, just replace the entire distributor. They're pretty cheap, and it's probably not worth it to tap out the pin holding the gear to the shaft, then tap it in with the new gear, unless you want to (I didn't, so I bought a rebuilt distributor from Rock Auto).



Joseph