Runs great UNTIL vacuum advance line is connected
#41
I run 18 degrees initial advance with my stout cam and it loves it - Vacuum can is in play as well. Runs perfectly as well. The factory spec was for emissions and mine would not run at all at the factory spec. Give it more initial advance and make sure you have the correct vac advance can for your application. - Go back to the LARS method.
#42
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I'll pull the cap, rotor, points, and ignition shielding to get a good look at the distributor base plate. Is it possible to see that internal ground wire? If so, I could check it for continuity. And what would cause the coil to short out internally as the breaker plate rotates? Would that be due to a loose ground on the plate also?
The coil wire that can short out is the small wire terminated on the negative post of the coil on one end, and terminated on the insulated terminal of the points with the condenser wire inside the distributor. This negative post wire is routed from the coil post, down below the distributor, and then up through a hole in the distributor body and then up around the breaker plate, before terminating on the points (or electronic trigger). This wire can suffer from age and heat related cracked insulation anywhere along it's length, and short on the manifold, the distributor, the breaker plate, or even the tin. Shorting this wire is an effective kill switch, and an intermittent vibrating short as the vacuum advance moves the breaker plate and pulls on the wire used to be a common problem with high mileage engines. Many times the rubber insulator plug at the coil wire entry hole gets cooked and deteriorates, and with time the wire insulation rubs through. Pulling or pushing the wire moves the rubbed insulation location away from the hole where it grounds, or away from the breaker plate where it can also rub and fail to insulate the wire. Sometimes it's good preventive maintenance to replace this wire and eliminate age and wear as a potential problem.
Photos of the wire & plug (thanks to Joe Fisher's reconditioning paper):
#43
#44
Melting Slicks
You don't have to do anything fancy to tell if the breaker plate is grounded. With the engine running with the vacuum advance connected, simply raise the window on the distributor cap and poke one end of a jumper wire in and touch the adjusting screw on the points while the other end is grounded to something outside of the distributor. If the engine suddenly runs correctly, you know the point plate wire is broken. If no change, the problem is elsewhere.
#45
Safety Car
It can vary a little. My open chamber aluminum head BB is limited to 36 (initial + mech advance) and 8 vacuum for a total of 44 deg since any more than that it will miss constantly (or trailer hitch as others call it) at highway cruise speed. But the open chamber heads are really more 70s era technology than 60s. But unless you really set up a modified distributor to allow something like 18 -- 20 degrees initial timing, vacuum advance is definitely your friend on the street.
Could it be that your "trailer hitching" is being caused by lean condition?
#46
Safety Car
I run 18 degrees initial advance with my stout cam and it loves it - Vacuum can is in play as well. Runs perfectly as well. The factory spec was for emissions and mine would not run at all at the factory spec. Give it more initial advance and make sure you have the correct vac advance can for your application. - Go back to the LARS method.
#47
Safety Car
You don't have to do anything fancy to tell if the breaker plate is grounded. With the engine running with the vacuum advance connected, simply raise the window on the distributor cap and poke one end of a jumper wire in and touch the adjusting screw on the points while the other end is grounded to something outside of the distributor. If the engine suddenly runs correctly, you know the point plate wire is broken. If no change, the problem is elsewhere.
#49
Melting Slicks
Another item that can cause the condition that you describe is rotor tip to distributor cap terminal alignment. The position of the rotor tip in relation to the terminal in the cap changes when the advance unit changes and in some units that are not aligned properly to start with will be off by quite a few degrees at full vacuum advance. Enough to cause ignition charge to seek neither terminal if it occurs far enough away.
You can look into this by setting the distributor at the exact degree that opens the points. The rotor tip should be near the terminal in the cap. Now add full vacuum (with a vacuum pump) and see how the alignment changes. The rotor tip should still be very close to the terminal.
If you have a LOT of degrees of change in the vacuum advance unit, it could cause this problem.
You can look into this by setting the distributor at the exact degree that opens the points. The rotor tip should be near the terminal in the cap. Now add full vacuum (with a vacuum pump) and see how the alignment changes. The rotor tip should still be very close to the terminal.
If you have a LOT of degrees of change in the vacuum advance unit, it could cause this problem.
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big block ken (07-10-2018)
#50
Race Director
I would think that large volume heads like yours have a longer burn period than closed chamber BB heads, and certainly small chamber, 58 - 64cc SBC heads; therefore more spark advance needed to get max cylinder pressure where it belongs.........at around 14* ATDC.
Could it be that your "trailer hitching" is being caused by lean condition?
Could it be that your "trailer hitching" is being caused by lean condition?
#51
Burning Brakes
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AND THE WINNER IS.....Critter!
Another item that can cause the condition that you describe is rotor tip to distributor cap terminal alignment. The position of the rotor tip in relation to the terminal in the cap changes when the advance unit changes and in some units that are not aligned properly to start with will be off by quite a few degrees at full vacuum advance. Enough to cause ignition charge to seek neither terminal if it occurs far enough away.
You can look into this by setting the distributor at the exact degree that opens the points. The rotor tip should be near the terminal in the cap. Now add full vacuum (with a vacuum pump) and see how the alignment changes. The rotor tip should still be very close to the terminal.
If you have a LOT of degrees of change in the vacuum advance unit, it could cause this problem.
You can look into this by setting the distributor at the exact degree that opens the points. The rotor tip should be near the terminal in the cap. Now add full vacuum (with a vacuum pump) and see how the alignment changes. The rotor tip should still be very close to the terminal.
If you have a LOT of degrees of change in the vacuum advance unit, it could cause this problem.
I first connected a Mityvac pump to the vacuum diaphragm and the advance plate moved immediately and held at 15" of vacuum. And THEN my eye caught the ROTOR. I've used "extended tip" rotors in the past without any issues, but this one must have wacked the inside contacts in the distributor cap, which knocked it way out of alignment. And the result was just as Critter described above. It must have happened immediately upon start up after the tune up. You can see a chunk of plastic that got shaved off next to the rotor tip. As soon as I replaced it with a shorter tip rotor, which I had removed, everything went fine.
I've got it timed at 12* advanced at 650-700 rpm idle. Dwell holds at 30* and I've adjusted the carb for maximum vacuum of @ 22 which is pretty steady. Vacuum advance connected works fine. I'll take it for a test drive tomorrow, just to make sure that I have the timing where it belongs. And from now on, no more extended tip rotors.
THANKS TO ALL OF YOUR FOR YOUR SUGGESTIONS. It sure was informative!
#53
Melting Slicks
CONGRATULATIONS! YOU HAVE SUCCESSFULLY DIAGNOSED THIS ISSUE!
I first connected a Mityvac pump to the vacuum diaphragm and the advance plate moved immediately and held at 15" of vacuum. And THEN my eye caught the ROTOR. I've used "extended tip" rotors in the past without any issues, but this one must have wacked the inside contacts in the distributor cap, which knocked it way out of alignment. And the result was just as Critter described above. It must have happened immediately upon start up after the tune up. You can see a chunk of plastic that got shaved off next to the rotor tip. As soon as I replaced it with a shorter tip rotor, which I had removed, everything went fine.
I've got it timed at 12* advanced at 650-700 rpm idle. Dwell holds at 30* and I've adjusted the carb for maximum vacuum of @ 22 which is pretty steady. Vacuum advance connected works fine. I'll take it for a test drive tomorrow, just to make sure that I have the timing where it belongs. And from now on, no more extended tip rotors.
THANKS TO ALL OF YOUR FOR YOUR SUGGESTIONS. It sure was informative!
I first connected a Mityvac pump to the vacuum diaphragm and the advance plate moved immediately and held at 15" of vacuum. And THEN my eye caught the ROTOR. I've used "extended tip" rotors in the past without any issues, but this one must have wacked the inside contacts in the distributor cap, which knocked it way out of alignment. And the result was just as Critter described above. It must have happened immediately upon start up after the tune up. You can see a chunk of plastic that got shaved off next to the rotor tip. As soon as I replaced it with a shorter tip rotor, which I had removed, everything went fine.
I've got it timed at 12* advanced at 650-700 rpm idle. Dwell holds at 30* and I've adjusted the carb for maximum vacuum of @ 22 which is pretty steady. Vacuum advance connected works fine. I'll take it for a test drive tomorrow, just to make sure that I have the timing where it belongs. And from now on, no more extended tip rotors.
THANKS TO ALL OF YOUR FOR YOUR SUGGESTIONS. It sure was informative!
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big block ken (07-11-2018)
#54
Race Director
How do the terminal posts look inside the cap?? Maybe some damage/nicks there too. May want to check.
Larry
Larry
#55
Melting Slicks
Wow, that brings back an old memory. Back when I was drafted into the U.S. Army, I drove a '62 tri-power 406 Ford that I hide in a nearby town in Georgia while in basic. One weekend I drove home to see my girl and I made it home okay but on the way back, I got as far as Orlando when the car started running badly. It had dual points and as an amateur mechanic, I sometimes struggled to get them set properly. They were my first suspect as the problem and I pulled into a gas station and borrowed a few tools. I'd pop the distributor cap off, yank off the rotor and had someone bump the motor over while I watched the action of the points. I checked their gaps, the rubbing blocks, the connections, but everything seemed fine. But whenever I put the rotor and cap back on, it ran terribly. I replaced the capacitor but that did nothing. I struggled with it for over an hour before I spotted the tip on the rotor whacked out of position just like the one in this thread. Replaced it and we were off!
#57
Burning Brakes
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I don't know if it was just mid-year big blocks or what, but I recall reading about extended tip rotors being used to make sure that there was good contact with the distributor cap contacts inside. And I've used them in the past. I wonder if the distributor cap is more narrow up top?! Weird!
#58
Great job, I am glad you got it fixed. You gotta wonder where the tune up parts were made, that seems to be the biggest problem now a days.
#59
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I'd have to explore a little further. I'd straighten the rotor tip, reset the rivet and re-install the rotor and see what happens.
#60
Safety Car
Glad you finally removed the cap and saw the obvious. Had you done that from the beginning you would have denied all of us the joy of racking our brains trying to find a nonexistent gremlin.
An entertaining and therapeutic brain buster for all of us.
Now check the shaft for wobble, and don't forget to reset your timing, because (maybe.........or.......not)it should be advanced by about 30 crank degrees after you straighten out your rotor tip. Congratulations: perhaps (or, not) you have stumbled upon a solution to the mysterious and elusive problem of distributor gear dimple alignment. You might want to patent your new invention
An entertaining and therapeutic brain buster for all of us.
Now check the shaft for wobble, and don't forget to reset your timing, because (maybe.........or.......not)it should be advanced by about 30 crank degrees after you straighten out your rotor tip. Congratulations: perhaps (or, not) you have stumbled upon a solution to the mysterious and elusive problem of distributor gear dimple alignment. You might want to patent your new invention
Last edited by 65tripleblack; 07-11-2018 at 12:10 PM.