Stumped on an engine "miss"!!! 390 FE Ford

Leave the vacuum advance off of it and enjoy.

Seriously.

 

broken diaphram and or to much timing.If it has mechanical and vacuum,you should be ok for now with mech.

 

If it's got the stock ford distributor, with either points or pertronics conversion, then it still has the original advance plate inside the distributor. The advance plates, over time wore a notch in the side of the advance slot, allowings the plate to move sideways, and change point gap, or pickup clearance, causing power loss and missfire. Install a new advance/point mounting plate, and I think your problem will go away. Please post your results. Good luck

 

HEY GUYS HE SAID THIS IN HIS SECOND POST-

Hmmm. I plugged BOTH vacuum ports on the carb and left the dist. with -NO- vacuum advance and it runs PERFECT!!!!

Too much advance at cruise. Like Claymart has been trying to tell you.
All you have been doing is setting your initial timing, you have no idea how many degrees your mech curve adds in OR how many degrees your vac adds. But its too damn much. Basically the advance is so far ahead, combustion is trying to stop the piston before it's at tdc.

And like lewislynn noted, here is the big problem-

I got the timing set at first with my timing light and had 14" of vacuum, and then put the light down and adjusted the dist to get my 16.5" of vacuum

Ah...WHY? Set the timing with the light PERIOD. You turn a dist to get the best vac at idle and you WILL overadvance it, causing the problem you have. Use the idle mix screws for best vacuum.

 

Thanks saving me the trouble, bud
Jeez oh Pete.

OP, get yourself a dial back timing light if you're going to do this stuff

 

Sometimes too much vacuum advance will cause the spark to jump to the wrong terminal under the distributor cap. The rotor within the distributor moves with the mechanical advance, so that the rotor maintains it's position with relation to the distributor terminals as the mechanical advance changes. However, the breaker plate that is moved by the vacuum advance does nothing to change the relationship of the rotor to the distributor cap terminals. If you have a worn distributor, or the vacuum advance plate has some play, it is possible that the advanced spark jumps to one of the adjacent terminals and causes a misfire.

 

My father had a 390 that skipped. He tried everything he could think of and got nowhere. He did find a spark plug wire that arced to the air cleaner, by looking at it in the dark. Also he found out that the real issue was the distributor shaft moving around. They had lubrication issues, and the bushings would wear. So to eliminate that one simply try to shake the shaft from side to side. Movement means it's changing the gap as it spins.
Good Luck.

 

deleted, repetition.

 

I'd try a new distributor cap. A crack, even one you can't see, can cause spark to jump to wrong post under load.

Scott

 

I had exactly this same problem on an English made Buick 215 motor. (Rover) I put the vacuum advance on the manifold port at some stage and then had the erratic farting, popping, cracking, roughness. I never connected the two together and messed about for weeks trying to fix it, and went as far as buying another distributor, and eventually a new Edelbrock intake and carb, nothing fixed it.

Then I read somewhere that manifold vacuum was too fierce for the vacuum advance system on this particular distributor, and it would cause the above mentioned problem.

I switched the pipe it onto ported vacuum and that sucker ran sweet as anything!!!!!!!

 

If I had my 'druthers I'd set the timing with a timing light so I knew what my initial, vacuum, mechanical and total advance were. However, setting timing with a vacuum gauge can be a valid alternative. But nearly everyone who posts that method here suggests advancing the timing at idle for maximum steady vacuum and then locking the distributor down.

The method I remember being taught years ago was to advance the timing for maximum steady vacuum and then slowly retard the initial timing to bring the vacuum down about 1.5" to 2" from its highest reading. If too much total advance is causing a miss or pinging this may be enough to alleviate the problem.

 

Well, I haven't given up on this car YET, but the "prior mechanic" told my friend that my problem just isn't right and that I didn't know what I was doing!!!
So, as of right now, it is in my driveway,and I told my friend to have her "mechanic" bring her happy ass over here and prove me wrong!!!
I'm on a pause on it right now, and have been concentrating on my '32 sedan instead. thanks for all the advice, and I'll post up the results when I get some.
Thnks again guys, Ken

 

O.K., update. Mechanic said it needs a "tune up" I said WTF, thats what we are all standing here waiting on you to do, since you said I didn't know what I was doing!!!! So she left!
Anyways, I went and bought -another- set of points, condenser, re-set the gap, got rid of the chrome coil and put on a KNOWN good O.E. Ford coil, and all is great! Car runs good, sounds good, and my friend is as happy as can be. Don't know if it was a bad set of points, a bad condenser, or the chrome coil just not doing it's job, but the car is done and my friends wife is happy!!! Thanks guys, I learned some stuff, I wrote some notes down of how "YOU" guys check and do things relating to engine troubleshooting, and I walked away learning a little more.
Ken

 

Full 12v at the coil with our stuff is only correct IF it has the right coil for the application (we make quite a few different coils)
We do not offer cap and rot r for stock distributors, so someone pieced this "Gift Package" together, not PerTronix, so it might not have the right coil.

Due to huge manufacturing tolerances on the Ford distributors over the years, not to mention wear, this sometimes is necessary, but since he put the points back in and the problem didn't change, this isn't the issue with his.

We do not have any sort of a 1/16" clear plastic disc in ANY of our kits. We do include a small plastic Strip that is used for checking the air gap when you set up the module, but it isn't round nor does it have a hole in it
And again, it depends on which coil you have, and which module as far as voltage goes.

 

---Full 12v at the coil with our stuff is only correct IF it has the right coil for the application (we make quite a few different coils)
We do not offer cap and rot r for stock distributors, so someone pieced this "Gift Package" together, not PerTronix, so it might not have the right coil.----


That very well could be the case. I didn't mean to "infer" that Pertronix put it together for her, Her husband (my friend) was the one who gave the gift package to her, and he has passed away, so I have no way to know for sure what all was and wasn't included, as far as which pieces were from a parts store, and which pieces were from Pertronixs. I am just going by what info she gave me. like I said, it runs great and she's happy so thats all that I am concerened about.

 

I'm running a 390, with a petronix, full 12 volts at the coil, 650 edelbrock in a T-Bird and the only thing I see you doing different is timing. I set my timing at 3 degrees with the vacuum disconnected, I bumped it up to 10 degrees and it runs better. I also have the vacuum line on the left port on the front of the carb. Old shop manual said you shouldn't have more than 18 degrees total timing.

 

Well I'm no Ford expert so I might be sticking my foot in it here. But I'd guess that the total timing (initial plus mechanical advance plus vacuum advance) should be something like 30 to 35 degrees. Maybe you'll end up with something like 8 degrees initial, 10 degrees vacuum and 16 degrees mechanical for a total advance of 34 degrees.

 

I had trouble with my '65 Studebaker today. Sputtering much like you decribed early on in this thread. When we found no spark from the distributor cap to three spark plug wires. When we took the cap off we found a piece of clear plastic material. This was supposed to have been attached so that the magnets did not fall out. Since this plastic strip was not in place three magnets fell out thus there was not fire to those three cylinders. I have had a Pertronix system on my Studebaker pickup for several years and have had not problem. The unit on my '65 is only a few months old, but the car really has only been on the road since June. I have never heard of this problem before.

 

My 64' Montclair 390 2 bbl with pertronix ignition was sputtering along until I removed those champion spark plugs (new plugs) and put in some autolites. Along with all the other tweeks, like a pertronix coil and direct wire from key switch - runs smooth now.

 

Wow, long adventure. but, lots of good info/ideas. one thing that would help in threads like this is some pics of motor too, helps to have some type of visual. yep, difficult for anyone to try to repair a ride that others had done work to. we all have our own quirks, as do our rides. have run Pertronix with no problems. but, with any add on it is best to run a complete set up like with a points conversion & coil. to throw more info into diagnosis in the future is make sure battery to truly good. a bad battery can cause a good running motor to run like crap under any load. my wife's '50 Chevy PU with a Chevy ZZ4 crate motor runs perfect with no vacuum to factory distributor.

 

I know the problem has been resolved. I just wanted to comment on why vacuum advance is used. Engines run better with the timing advanced but they start harder. Old cars had hand controls for spark advance because they wanted them to fire after top dead center when hand cranking them so drivers didn't get their arm broken starting them. They had to constantly be adjusted as engine speed changed.

The vacuum advance is a good way keep the timing backed off until the engine starts. If the vacuum is connected to manifold vacuum, it advances the timing as soon as the engine starts and builds vacuum. As the throttle is opened, the engine vacuum decreases because the airflow has less restriction. This is where mechanical advance comes into play. The faster the distributor turns, the farther the timing is advanced until the limits are reached. The combination of vacuum and mechanical play out as the throttle is opened or closed.