47 V8 ignition mystery

What inside the distributor would cause only the same cyl. To misfire???
The rotor not getting spark to the cap prong or cap contact,,,if rotor to contact is to great it would probally fire intermintally,,,what would cause gap to change??
Possibility the bushings,shaft could be a little off!maybe one lobe on shaft cam could be worn down just enough to cause misfire,,,,,any of these things would cause only one cyl to misfire,that is assuming he has checked the wiring and caps ,plugs etc. which he say he has,,,,I say rebuild the distributor COMPLETELY,,,!!
 
Think he said early in post that he put a timing light on # 6 wire and it was misfiring.
 
Terry said:
Watching the flashes from a timing light at idle, (either in line or clamp on type) can indicate which cylinder has a firing problems. Look for missing flashes using a good cylinder as reference. If all the cylinders appear the same, what was your vacuum reading at idle? Should be very close to 20 maybe slightly lower like 18 and very steady. While you have the vacuum gauge attached adjust carburetor idle mixture screws, while enging is warm,g for the highest and steadiest vacuum reading and engine running smoothest. The screws should be about 3/4 to 1 turn out from full close. Small adjustments should make a big difference. If the adjustment can not be gotten or out of adjustment range or screws don't make a difference the problem would appear to be in the Carb. Hard to believe the engine running rough and the vacuum gauge not reacting at idle. While driving the gauge should be moving low and high with acceleration and deceleration IMO Your postings don't seem to give enough information on what your doing or seeing.
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In response:

Reading the timing light for each cylinder shows #6 missing the most followed by #3 some and #7 & 8 very rarely.

This video shows the vacuum gauge at full idle, i.e. throttle closed completely, at highest and smoothest RPM by adjusting idle mixture screws. https://www.youtube.com/shorts/5UoexytEWQk

Vacuum gauge moves down with acceleration and up with deceleration and is steady except at full idle.
 
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Don said:
What inside the distributor would cause only the same cyl. To misfire???
The rotor not getting spark to the cap prong or cap contact,,,if rotor to contact is to great it would probally fire intermintally,,,what would cause gap to change??
Possibility the bushings,shaft could be a little off!maybe one lobe on shaft cam could be worn down just enough to cause misfire,,,,,any of these things would cause only one cyl to misfire,that is assuming he has checked the wiring and caps ,plugs etc. which he say he has,,,,I say rebuild the distributor COMPLETELY,,,!!
Click to expand...

The distributor and coil are creating reliable and steady spark as shown by HT wire from coil near head bolt when cranking and steady spark to all plugs except #6 mostly, #3 a little and #7 & 8 very rarely when running. Problem spark locations do not change with swapping spark plug wires or distributor caps. Rough running doesn't change by unplugging any plugs.

The distributor is a Ford remanufactured sent to Michael at 3rd gen who just set the dwell that was off and replaced the condenser and sent it back.
 
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slowforty said:
You could just loosen the bolts in the manifold and slip a piece of metal under the carb to block off the heat riser.
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Brian has also mentioned the heat riser but I don't understand what that has to do with the engine running rough. I would not want to run my car at below 0 temperatures without the heat risers.
 
Tonight I tested for vacuum leaks around the manifold and carb as follows:

Ran the engine at full idle speed (throttle plates totally closed).
Squirted some starter fluid into the carb to make sure it would affect the RPMs.
Removed the wiper vacuum hose and squirted starter fluid in there for the same reason. (Both changed the RPMs)
Reconnected the wiper vacuum hose then sprayed the starter fluid all around the edges of the manifold, where the carburetor connects to it, and around the carburetor throttle shafts. No change in RPM by any of that. Would seem that I have no vacuum leaks causing the rough running.

Other ideas?
 
>>>I've only got three weeks to solve this problem before I have to put Old Henry in a coma for two years while my wife and I go to serve voluntarily in the Philippines for two years.>>>Other ideas? >>


Only ~2 weeks now. Seems like time to wrap it up. Focus on preparing for the trip. Worry about the car when you get back and have more time.


Meanwhile just keep running MMO. Maybe arrange for a friend to start & fast idle till it heats up every week or so while you're gone..
 
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https://www.jalopyjournal.com/forum/attachments/vacumm-reading-1-png.4613289/


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Your vacuum leak test with starter fluid; you've checked the base of the carb area, but I don't see where you have checked where the manifold bolts to the block. The vacuum gauge certainly shows very low vacuum, which could well be indicative of a vacuum leak. Bear in mind, this vacuum leak could be internal; there can be a vacuum leak into the valley, or that heat riser could have cracked...I have experienced this.
 
Other than a bit of flutter, late valve timing seems closest. Maybe worn down cam gear teeth especially if fiber?


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Well, it looks like we have finally concluded that the rough running is nothing to do with anything exterior like ignition, carburetion, or external vacuum leaks. Everyone now seems to be suggesting that it is a problem within the engine itself requiring partial or complete disassembly. That I don't do and won't have done in the two weeks I have left of life as I know it.

So, I've put Old Henry into his coma for the next two years, unplugged the clock so it doesn't get another two year's wasted wear, removed the batteries from the outside and inside thermometers, disconnected the voltage booster, put fuel stabilizer into the gas tank and filled it up, gave him a nice hot bath, and topped up the oil. Might even consider putting it up on jack stands to save flattening the tires.

My son lives close and will come monthly to run all vehicles while he's otherwise checking the property inside and out just like he did when we were in Hong Kong for 18 months a couple of years ago.

Anything else to make Old Henry more comfortable in his coma?
 
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