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Discussion Starter #1
Long time owner of a 67 390 gt 4 speed fastback. It's been a very reliable runner for 20 plus years, but the past 6 or 8 months i've developed an issue which i need some input if anyone has had any similar issues. Seems in warm weather like now in the midwest, after the car has run for maybe 10 or 15 miles and is good and warm, it develops a stammer pulling out of first gear from a stop. Alternatively, it also stammers going up a hill or incline at a good speed 40 to 50 mph's while it's been up in fourth gear for an extended distance(at least a mile or two without and downshifts). The stammer, or hesitation probably a better term, is accompanied by a backfire. Initially when it started, i got the wiring around the manifold and valve covers all replaced. There was some old splicing that was in need of updating etc. Theory was when things got hot something was touching something hot. Didn't stop it. Also replaced the clutch bearing on what is a newer Ford Performance clutch as we thought possibly it was not disengaging when it gets real warm coming out of first gear. I'm not a mechanic by any means, but an old car lover like probably a lot of guys in their 50's. Does anyone have a similar experience, or does the backfire which is accompanying it mean anything to any of you old Ford veterans out there? It's odd because it 1. won't do it while the car is relatively cool( was ok in winter), and 2. the car has not to this point just shutdown. Any thoughts or ideas appreciated. Love the car, and it runs great other than this recent tough one to call. It has original wiring from the dash, etc. so i'm guessing it could be some sort of other connection issue?
 

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Don, does your car have points & condensor ignition ? How is the ignition coil ? I'd be checking out ignition before I suspected other problems. LSG
 

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Discussion Starter #3
Yes, still has the points, etc. No Pertronix here. That's what i was thinking as well today.
 

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Discussion Starter #4
Sorry guys i posted two threads as the first one didn't show up for a while. Trying to delete the first one. Not a big computer guy!
 

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Either an ignition issue (points, condenser, rotor, cap, coil, tune-up) or fuel issue (filter, carb). Lots of possibilities. I'd do a tune-up first and see how the engine responds.
 

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Discussion Starter #6 (Edited)
I've not had an issue like this on what is otherwise a really good running car. I purchased a rebuilt Holley 715 cfm i believe if my memory is right from Pony Carbs probably 20 years ago when i bought the car and it's been flawless. The fact that it seems to do it when it's moving out of a stop or up a hill seems like something is loose which is frustrating to say the least. Once you get out of first from the stop, it runs flawlessly unless you head up an incline (and it's either the grade) or the added strain/vibration of having to get up the grade. Head scratcher.to say the least.
 

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I've not had an issue like this on what is otherwise a really good running car. I purchased a rebuilt Holley 715 cfm i believe if my memory is right from Pony Carbs probably 20 years ago when i bought the car and it's been flawless. The fact that it seems to do it when it's moving out of a stop or up a hill seems like something is loose which is frustrating to say the least.
Hot makes it sound electrical.. that being said, a carb that has been on for twenty years probably needs a quick rebuild. I did mine a few weeks ago and couldn’t believe what came out and how much better it runs after the rebuild. Very easy to do btw.

Thanks,
 

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Discussion Starter #8
Yea, i'm convinced it's electrical. Could be the coil is getting long in the tooth and the heat is compromising the situation. I had thought the clutch bearing was the issue until it did it on a hill in fourth gear at 50 mph. That kind of ruled that out. I'm inclined to go the coil/points/etc route first and see what it does. Old cars, you've got to love'em! LOL
 

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Absolutely, positively buy the best ignition products on the market- Blue Streak by Standard Motor Products. Absolutely, positively no cheap chinese crap. The Blue Streak parts will cost more but you get what you pay for. Do not let anybody tell you "this Brand X part is just as good as Blue Streak". They're lying through their teeth.
Do you understand, Blue Streak?
 

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I had a similar issue and I think I traced it to adjusting the floats in my carb.
 

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My first thought is do a tune up, plugs, point/condenser ,or switch. Maybe even wires.
Then I'm leaning towards carbs running to lean. When pulling plugs, look at them to see how they're burning.

FYI, I also have a factory 67 390, 4spd, vert. welcome...
 

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Check the physical condition of the breaker points then toss a dwell-meter on it and check to see if it has 27-31* of dwell. If not, regap to .017" and re-check. If dwell is okay or if you regap and it still has the same symptoms, replace the condenser (since they're a) inexpensive and b) difficult to test properly unless your multimeter supports readings in microfarads. If, after replacing the condenser, you STILL have the same symptoms, grab your ohmmeter and check the ignition coil primary and secondary resistance. Primary should be around 1.5 ohms and secondary can vary widely but typically between 7.5k ohm to 15k ohm. You can also repeat the test with the coil hot after a short run. If coil resistance checks out then check the resistance of each spark plug wire and the coil wire. Specs for the number of ohms per inch, foot, etc., are usually available at the manufacturers support page. If THOSE are okay, check the resistance of each spark plug... you don't have to remove them, just connect your black lead to the block and touch each plug's 'button" with your red lead. Same deal... plug manufacturer will give the resistance specs somewhere on their website. If you STILL have problems, check the inside of the distributor cap for cracks or carbon tracks and, lastly, check the routing of the plug wires to cylinders 7 & 8 to make sure inductive crossfire isn't an issue. These 2 wires should be separated as much as possible.... if you have wire looms on the valve covers they should hold the wires 7-5-6-8 in that order and if 7 & 8 must cross it should be at a right angle with at least 1" of separation.
 

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Discussion Starter #13
Thx for all of the suggestions. I'll post once i see what comes of the new ideas. Has anyone swapped out the old school points etc, for the Pertronix or similar type setup on their S codes? I was curious what product and experience they had with it. I'd not contemplated it as i've had really good luck with my car for many years as it is setup. I did put a Pertronx on a 64 gto i have with a 389, and it's performed very well.
 

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I've run a Pertronix II in my 67 390 stang along with the matching Flame Thrower coil for ~ 15 yrs, no problems. There are different versions of Pertronix.
 

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I installed DuraSpark with wiring kit, coil and box from NPD. Fires right up and I like the built-in spark retard at start as these engines have a high compression.
Edit: Plus, if anything goes wrong you can get replacement parts at any parts store.
 

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Discussion Starter #16
Does everyone use dual points with their setup? I hadn't pulled the thing apart yet but i didn't think it was a single point setup. Anyone know off the top of their head?
 

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On my 67 GT 390 I added tri-power, a Ford setup from mid 60's. With tri-power setup, it doesn't have the needed "ported vacuum" for the vacuum advance on the stock 390 distributor. What Ford used was a "dual point" mechanical advance distributor. Lucky enough to find one. I took the points set out and installed Pertronix II for dual points. Works fine.
 

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Duraspark on mine.
 
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Sixty7vert, you don't have vacuum advance at all ? LSG
NO! no place to hook a hose...

My Ford distributor casting number is either:
# C2SF-12127-B 390 6V tri-power only or
C5AF-12127-AV, dual points mech advance

I forget which, bit tough to see #
I wanted a period correct Ford setup. Runs just fine 16 yrs. I do still have the orig 67 390 distributor all rebuilt, put away
 

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