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Last night I tried to drive the car, and when I hit the gas it shuddered and made a banging or popping sound. The loss of power was very abrupt. It happened whenever I got on the gas. I turned it off for an hour then started it, and even at idle I could hear a popping noise. I drove home gingerly, and did not notice anything. The engine was running well for the last 3 weeks, although I have been burning a lot of gas. 20 gallons in 100 miles (this is estimated I have a broken speedo cable) I have an MSD ignition, and Holley Carb. Right now I suspect electrical, but I am not sure what to check first.
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I'm far from an engine guru, but I'd pull a few plugs to see if you're running lean or rich. I'm assuming the popping is backfiring and not afterfire, and that you're running lean or the timing has gone off. I'd start with the fuel filter to make sure it isn't clogged and restricting flow, check the float level, the fuel lines, needles and seats (often something will keep them open and flood an engine, maybe something is blocking and restricting flow) etc. ... some carbs have an integral (or in-line) fuel filter at the fuel inlet - check your carb specs - if that's the case, check that it isn't clogged. If you have or can borrow a spare carb, swap it out and see if things change.
Then check your timing to make sure it hasn't gone way out of whack.
Let us know what the plugs look like.
Thanks guys I'll update you when I have the time to look into it. I might be able to pull the plugs today. If I check the distributor pin, then I will have to redo the timing right? That will mean pulling the bulkhead.
Here my current list of possibilities.
1) Timing is messed up because of a sheared pin.
2) Spark plugs are fouled. (missing and backfiring)
3) Lean or Rich (check plugs) I will post a photo
MSD box is bad or badly wired.

I had to drive about 3 miles home, and it ran alright. I accelerated in 3rd at a reasonable rate. It had been popping a bit at idle, but as I drove it seemed to improve. That was an hour after I tried to go for a spin and wanted to accelerate hard and it was bad.
Last edited by icole
The plugs aren't out yet. I am home with my kids. I removed the air filter and discovered that I do not have a choke. The engine idles fine, but when I pumped the gas the bang turned out to be blowing out of the carburetor. My online research suggests timing, or dirt in jets. Any suggestions would be great. I will pull 2 plugs and photo them when the kids are in bed.
Do our distributors use vacuum advance for the timing?
Last edited by icole
Backfire through the carb can also mean bad plug wires that are misfiring / crossfiring. You really need to start with the basics and work your way up to the more complicated reasons. Do an electrical tune up with new cap, rotor, points (if you have them), wires & plugs. That way, you know these are good. Check all of your vacuum hoses and make sure they are not old and cracked, and any open ports are capped. I recall your brake booster is gone, so that big port should be capped at the manifold, along with the little port on top of the big nipple.

Set up your bulkhead so you can pull it in a few minutes so that is not a deterrent to maintenance. The seat belt bolts can be the only thing holding the decorative cover, and the steel bubble can be held with only a couple of bolts. 5 minutes and your covers are off.
I can try new plugs wires etc. It is frustrating, because it ran fine before. It idles fine and I can slowly rev it up. When I step on it if does it. I did not switch the plug wires so I know they are on the right plugs.
What is this. The plug on the right with 2 wires is very loose. I can't even feel the spades going in when I unplug and plug it back in.


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icole, one of every new Pantera owner's first problems is figuring out what the previous owner did, and why. The most problematic area is usually wiring. Sometimes, that requires tearing everything out, sitting down with wiring diagrams (factory, MSD, etc.), figuring it all out and putting it all back in a way that YOU understand it. That usually requires putting everything back to stock, making sure everything works, then re-adding the aftermarket items such as MSD ignition boxes. You also want to install new crimp connectors yourself. That way, you know they're correct and making good contact. Oh, and get rid of those blue wire tap connectors. Those are the blue connectors with two wires on one side and one on the other. They're notoriously unreliable.
What is this. The plug on the right with 2 wires is very loose

That's the voltage regulator, I had wonderful problems with mine when I got my car, but as long as you're not seeing erratic things happening with your Tach, Ammeter (or voltmeter if it's been swapped), then nothing to worry about, just snug up the connections and it should be fine.

Sounds like you've got a laundry list of things to check, if you're in need of some local expertise - lots of deep skills on this forum, but sometimes it helps to have an extra set of eyes on the problem, you might contact some of the guys near Philly (Jon Haas of Pantera Electronics is an awesome guy to get to know), attached is a link to a Google map of some owners, I'd thought there were a few Philly guys there, but the closest plotted seem to be Baltimore MD and Monroe PA.
take Your Cat to a TRAINED Mechanic Who Does

Get references though, I took mine to a guy who works on many of the classic Mustangs in my area, it cost me a small fortune for little more than a tune-up and the problems I had were only partially solved. It was only when working with some fellow owners that we resolved the worst of the bugs, then me fiddling about changing some parts on the carb and tuning it a bit myself - Kudos to Marlin, his comments to me were on the money for a key source of the problems I was experiencing (no I'm not a mechanic, you as a science teacher most likely have more technical skills than I do). I used to be afraid of carbs, but watched 2 being rebuilt and went home tore into it and she's running better than ever ... I'm almost feeling brave enough to try a leak-down test on my engine this winter - just gotta find a YouTube video to reinforce my understanding of what I've read :-)

Don't despair, talk to a few guys locally - here's a link to the PI regional reps, call someone close to you (Steve in Maryland perhaps) and see if they can point you to someone in the Philly area who either knows engines, or if it comes down to the problem needing more skill than can be mustered locally, they may be able to recommend a reliable shop (I'd still suggest a call to Jon Haas at Pantera Electronics, he's the closest guy to you I can think of, but he likely knows of people closer).
Or the Eastern Panteras Association:

Finally, here's the worst fowled plug I've come across (not mine), the guy running this was shearing distributor pins like there was no tomorrow, but man could his car fly - The shot is here to show you what a tapered plug looks like (just remember what Marlin says about the type of heads and whether tapered plugs are right for you or not).


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don't mess with to many things at one time....sure if you have no basic skills in engine mechanics.
Now that plug is indeed fouled and how ! ... so you found a first problem.Place 8 new plugs and be sure to have the right type for your heads ( taper or flat ring )and temperature grade according your engine , as Marlin explained. And try running the car .See from there. The only thing you risk is fouling another 8 plugs but that isn't THE cost i suppose...
The engine idles fine, but when I pumped the gas the bang turned out to be blowing out of the carburetor

I'm 90% sure it's carb related. Ignition and valve springs come later. Just had a friend's Pantera that did exactly the same, reason was lack of acceleration pump squirt. Check with engine off and a mirror over the carb (not your face) that you have two strong squirts immediately after opening the throttle. If you don't that's the reason. You can normally adjust it (my friend's Pantera was misadjusted by a mechanic, when properly adjusted the problem was gone). Or it could be dirt in some passages or a loose squirter (big screw holding it down, visible in the mirror).

A paste from my web page:
" it’s critical to adjust end play when throttle is fully depressed. If end play is too much you lose pump action, if it’s to little you end up destroying the pump. End play is determined by opening the throttle fully (engine off) and then seeing how much further you can press the accelerator pump at the are situated on the fuel bowl. You should be able to create a gap of 0.4mm, adjust spring just above to obtain that."
The head is aluminum, and it has SVO stamped on the side. The plug 5754 is holding has a shorter reach. Is this the difference, or is there something on the seal itself that is different. If I get the same plug I have but with a tapered seat, and is there any harm if it should have had the washer?
Originally posted by MARLIN JACK:
...By the way...'What Heads are You running'??
Stock Cleveland heads take a SparkPlug with a 'Tapered' Seat! What head are You using a Plug with a Metal 'O' Ring Gasket, In?? And it looks to Me, that ring hasn't even been Compressed Fully to Seat! Are You running the Wrong SparkPlug? Most All Aluminum Heads take a 'Flat Seat' Ring Gasket, Sparkplug! NO Tapered Seat Plugs in Aluminum Heads; The Seat would Errode and The Taper Could Crack Them!...
Last edited by icole
My dad built this engine, and he build a lot of engines. As far as the amount of oil required to foul the plugs. Before I installed the PCV valve it had 2 vents, and was leaking oil out of the vent pretty badly. I put the PCV valve in and no more oil, leak. Maybe I am sucking too much oil out of the valve cover? It seams to me my best bet is to replace the plugs and put the leaky vent back on If it runs I will buy an oil catch for the PCV. As far as which plug the plug feels like it is going in all the way. It takes a lot of turns to get it tight, and I would be shocked if my dad who built 7 small and large block American engines, and 4 six cylinder outboard motors that I can remember would put the wrong plugs in.
Last edited by icole
Thanks Marlin.
It was early in the morning when I wrote that. The PCV valve I installed goes into the manifold, so to get to the carb the oil would have to go up steam. The Plugs are NGK. I know hotter plugs are less likely to foul, but will it resist fouling while burning a little oil.
If the drain backs are clogged would that starve the crank bearings? I did about 100 miles of hard driving before the problem developed, so I think that if I had starved the crank I would already have more serious problems.
I will do the other things, but I am going to try new plugs first. If it runs well with new plugs, then that is a start.
I will have the box checked. The distributor cap looks brand new, and I have another MSD cap in a box, so I know the current one is at least the second one since the rebuild was done 10 years ago. I had it off to get the trans out. The plug wires don't look as new.
Update. I pulled a plug from the other cylinder bank. It looked the same as the one I pulled last night, and it had oil around the end of it. It has been a few years since the plugs were changed. It is possible that it was not running perfectly and degraded slowly until the backfiring became noticeable. The oil level is not any lower than when I filled it 2 weeks ago, so I have not burned enough to notice a drop in the pan level on the dipstick. I am going to do new plugs and plug wires, and I found a cheap home-depot way to make my own oil catch can for the PVC line. I will update you when I get the new plugs and wires.
Thanks I had to get the same plugs because the guy at the auto store did not know an equivalent but hotter plug, and the current NGK R5671a-7 is the hottest they make. They do not have 6 or lower, which means higher in NGK world. I found out that the autolite 3935 is equivalent to the 7 but that is there hottest on that plug. If anyone knows similar plugs that would be great. If I find one with the correct thread and shape and an NGK heat rating of 5 or 6 is this all that matters, or are there other factors?
OK My wife had to go out, so I could only drive up and down the street once. It misfired once on a low RPM 2nd gear start, but starting in first ran through one two great. It took this long, because I cross threaded the first thread for the 7th plug I was changing, and had to wait for a back tap tool. I was not able to push too much, because it is stronger now than ever. In first the tires spun, and in second the clutch slipped, so I must adjust the clutch before I try driving anymore. I noticed that the air filter is hitting the two tubes that point out the top of the carb. I think it is meant to dome upward, but has collapsed downward. I am going to fix this too before I drive again.

The two tubes, the cover is hitting, are the Float Bowl Vents! You need a Minimum Clearance of 3/4 Inch over the Top of those, or your going to have problems. The 'Power is Back'! Did 'It' put a Smile on Your Face?...

Does it have to be 3/4" of nothing, because the K&N filter on top of it allows air through, unlike the stock setup with the Aluminum cover.
I have still only driven about 10 miles. It seems to be running better the longer I drive it. in 10 miles I sucked about 3 oz of oil into my catch can. Mind you I drove those 10 miles 1/8 at a time I was WOT or on the brakes the whole time. It is not running perfectly. If I step on it from bellow 2k rpms it hesitates. If I role on the throttle or quicly floor it above 2500 RPM it runs strong. I try to keep the revs below 6500, but it revs so quick from 4000-7000 sometimes I have gone higher. All is good in that high RPM range, and I think the low RPM response was improving, so maybe I need to drive it hard some more if it is nice Saturday. Thanks for all the advise and help Marlin.
I drove it all day yesterday. No more hesitation. It is running smooth and strong. I am still sucking a lot of oil into my PCV catch can. I am going to try mounting it higher than the valve cover to see if more will drain back into the engine. It has so much torque that when the tachometer hits 3500 RPM in second gear the tires start losing grip, and I have to let up on the throttle. Before I installed that catch can I must have been burning a lot of oil, but even before I put the PCV valve on it was not running this well, so the plugs and wires probably needed a change anyway. When I have more time I will pull the valve covers and check the oil drain holes. If they are clogged the problem is on both sides, because it doesn't matter which side the PCV is on it is pulling oil out. Of course the harder I drive it the faster it sucks oil, but that is because hard driving causes high vacuum in the intake. Thank you for all of your input.
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