Topic: Correct 68 S Code C-6 Dual Vacuum Advance

[WT8095]

In your original post you mentioned, "no amount of starter fluid will re-fire it". When you're trying the starter fluid, what does it do exactly? Does it simply spin? Does it try to fire intermittently? Does it spin at the normal speed, or is it slow?

When did the problem start? Did it run fine before the advance was changed? Did the problem start immediately afterward, or did some time pass? Do you have the thermostatic valve on the R/H exhaust manifold?

[70cj428]

Hi 68 S code,   Kinda a late comer to this post/thread, but I thought I'd add my 2 cents.....

If the engine won't fire on starting fluid, That's a STRONG indication that it's a spark related issue, not a fuel/heat issue. The first thing I'd change is the coil, especially if your running a repro yellow top coil, as they really suck, especially when heat soaked.

If a new Motorcraft coil doesn't help, I'd temporarily add a decent mechanical temp gauge, and know for sure what the coolant temps are running.

Lastly, If your running the dual diaphragm setup and are having idle speed (advance) issues, try another ORIGINAL thermostatic vacuum switch, as the repros suck for this part as well. You should be able to troubleshoot the advance system by initially hooking the port on the metering block directly to the outer advance port, and leave the inner advance port open. That should bypass the whole dual system, so you won't get the increase in idle speed at high coolant temps, but the car should behave normally otherwise once you reset the timing
...

Let us know how you make out....

John

BTW, I'd be surprised if your car came with a dual diaphragm setup with a C6, as that could be kinda a safety issue.... The dual diaphragm system/thermos switch setup was designed to increase the idle speed once the coolant temp got too high to aid in cooling. A sudden increase in idle speed on an automatic car could cause the car to lurch forward unexpectedly, another thing that could suck ....

[Daisy]

Aha!
I "think" you are getting your vacuum advance signal from the wrong port on the carb!

At idle it should stay at ~10 deg BTDC and it should go to higher as you accelerate the engine.

That it jumped >30 deg plugging the vacuum advance back in at idle - says you have the wrong port (depending on where you get vacuum on a carb determines when you get a vacuum signal... 

So - check the vacuum PORT for the advance.
It would explain why she is running hot and hard to start hot.

So.
Get the correct port.
Set timing
THEN set idle speed.

[WT8095]

...I'd be surprised if your car came with a dual diaphragm setup with a C6...

All S-code motors in '68 Mustangs used the C8OF-D distributor, which has dual advance. That includes auto and manual transmissions.

[68 S Code]

Yes i had heard that the repop yellow top coils look nice but were not great for a driver. An original had been restored and stamped but I don't think a 50 year old one is going to be dependable enough so I am currently using a MSD Blaster 2 high temp and high vibration coil. I also moved it off the engine onto the front apron using a screw which held the washer bottle next to shock tower. Some janky wiring leads for now using alligator clips and wire from harness and distributor to coil but it starts and runs in this configuration. I currently have a single diaphragm advance which was installed during the distributor rebuild by Tim O'Connor.

I think I made some great progress yesterday with the help of a friend. While waiting for him to arrive i happened to be reading the service manual engine section and specific problems. Under "Running Hot" it mentioned belt tension as a possibility. Decided to check the belts and guess what.....seems the belts stretched and way too much deflection. So readjusted the alternator. Once friend arrived we fired her up. Found out I was using the wrong edge of the timing pointer. Meaning I had used the top of the pointer and not the bottom which has the pointy end. All i can say is that whoever i trusted to get this car running were spinning that distributor without ever putting a timing light on it. Easily 10 degrees ATC when I had the drive-ability issue. So now "I" set the timing to 6 degree BTC (factory spec) and friend adjusted carb to idle at 650 rpm. It purrs at idle. I can shift it into reverse and drive without having to feed in gas to keep it from stalling. It acts like a "REAL" car The new NAPA sourced Vacuum Advance Control Valve may not be working. Currently the vacuum advance is running off carburator vacuum. Measured it at 2000 rpm and I have a reading of 55 degrees BTC. A bit high since spec is 41 degrees off the VACV once manifold pressure is allowed by the pellet moving. Engine is running at least 50 degrees cooler when I measured the intake manifold. Still a few degrees above 200 but it was easily idling for over an hour in the garage with nothing more than a small house fan blowing on the rad. Drove it for a mile today to get the steering wheel lined up after getting the new NOS turn signal switch sorted. Just because its NOS doesn't mean its perfect. Had to fiddle around with the connector pins but at least ALL the turn signasl and hazard lights work. Don't know why now the horn doesn't. It did with the old repop switch.Old cars!

Wednesday I plan to drive it for.....well as long as it allows me. I'm hoping at minimum an hour. Have my fingers crossed.

[Daisy]

Excellent!