It got worse with the timing advanced right?
Let me be sure;
1)The points are gapped and clean.
2)The timing and dwell are more or less rock steady, both at idle and when slowly building revs, up to at least 3500 in park/neutral.
3)The valves have been recently lashed.
4)It idles at 21inches.
5)The problem only occurs while driving,
6)It idles nice at 12*Before tdc,But then it seems like the ignition is breaking up, when under load.
7)It idles poorly at 2* BTDC, but runs fine under load.
8)It seems to be dropping 1 cylinder, when timed at 12*BTDC.
Does that about sum it up?
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Here's what I think. I think the engine got into detonation and cracked one or more sparkplug insulators.
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Before you do anything check the cap over for carbon tracks and cracks and that all the wires are fully plugged in and on, and that the wires are not shorting or crossfiring. This is best done in the dark(engine running). Also do a coil spark check. You CAN do this with a point type system. Simply pull the coil wire out of the dizzy and support it with an insulated whatever in such a manner that the spark will have to jump a gap of 1/2 to 3/8 inch to reach the engine block(ground). Then have a helper crank it. This works best with the plugs out, and in the dark.You can combine this test with the plug change. You are looking for a nice steady stream of sparks that sounds like a mini-welder.If the coil can do this ,the entire primary side is working, and the coil is most likely ok.I would put it out of mind for now.
Now this first question is extremely important; reread questions 6 and 7. Are they both absolutely true? If 6 and 7 are absolutely true, the engine may be experiencing way too much power timing.Go back to post #5. Don't miss the part about the vacuum advance can adding it's load.
2) If the problem can be traced to too much advance; Firstly, re-prove the Dwell is stable to at least 3500 rpm and that you used the correct 6 cylinder scale.Then,the next 2 question are; Is it worse at part throttle than at full throttle? and is it worse as rpm goes up? If yes and yes. Simply, put the timing back to 5*BTDC and defeat the vacuum advance can,then retest. If this brings things back into line, advance the dizzy 2 or 3 degrees and retest, still without the Vcan. Repeat until you have problems or the power timing gets up to 36* or so, at somewhere between 3000 or 4000. If it runs fine with power timing limited thus, you will need to modify the dizzy to make the 12* at idle and to also limit the powertiming.
But if it just gets worse and worse, even with the Vcan disconnected, and the dwell set right(don't even think about lash just yet), Then we have a problem. Either we have a valve spring issue or we have a cracked insulator on one or more sparkplugs, or the rotor has gone out of phase with the cap.
On a slanty, the easiest to check are the insulators. If the engine was run loaded under detonation, theres a good chance of this so pull them all out and look them over. Broken insulators are obvious, but cracked ones, especially cracked new ones can be very hard to see, especially as one gets older So dig out a bright lite, and a magnifying glass.If you can't find any cracks, I highly recommend that you replace them all, so we don't chase out tails around forever. If this cures the problem, with the timing back to 5*, you can put the old ones back in 2 by 2, until you find the bad ones.
But if new plugs doesn't cure it,the next easiest is rotor-phasing, so, lets get into the dizzy. Do you know how to check rotor phasing? This has to be proven now.
And finally, if the Dwell is correct and stable, the plugs are new, and the rotor is correctly phased,Then I would pull the valve cover, and check every spring for seat pressure. I would put #1 cylinder at TDC compression, and grab the springs(one at a time of course), and attempt to spin them around the valvestem.It should be quite difficult. Then rotate the crank exactly 1/3 of a turn and try the next one in the firing order. And so on until all six cylinders have been checked. Some slanty dampeners are marked at 120*. If yours is not, you will have to use the thumb in the hole trick. I cannot think past this point cuz going back to questions 6 and 7, this sequence should reveal the culprit(s).
But if I misunderstood and questions 6 and 7 are NOT both absolutely true, but in fact the engine breaks up either way, then go straight to the plug check, and if you have to, the valve spring check.
But in any case, the power timing has to be limited.
Once the problem has been solved, hook the Vcan back up and retest.
If absolutely everything is fine but the problem persists, it's time for a leakdown test.Now, personally I would have done this test, right after the spark test, and just before the new plugs went in. And if you've read this far, and have the tester, so should you.
Good luck,eh
