Since no one has responded, I'll try. My guess is that the warning refers to the possibility of "pinging", premature detonation of the combustion charge triggered by dieseling or hot spots in the combustion chamber rather than the spark plug firing. Its accompanied by a quite distinctive sound in the engine and nothing you've said so far suggests you're experiencing either pinging or its more damaging cousin knocking. I find setting point gap with feeler gauges a very hit and miss affair. Always use a dwell meter to check the result and do it again until you hit the correct gap measured in degrees open on the meter. Only then can you move on to timing the ignition without the possibility of the kind of issue you describe as the spark breaks down at the points at high revs. A dwell meter isn't costly and should be bought along with any timing light, as the light is redundant without the meter, imho.
OK, loosen the set screws, move the plate, tighten the screws, readjust point gap. You would be amazed at the difficulty I've had in locating a dwell meter here in Memphis... NAPA: not in stock but could order one Advance: not in stock, barely had a clue what I was talking about O'Reilly: see above AutoZone: Memphis is their corporate HQ - 4 stores visited - only one had a dwell meter in stock, you could tell it had been sitting around for a LONG time. I'll drop by again and pick it up today.
just switch them out? My rotors are the narrow kind but oddly enough one is more narrow than the other by about 30%! Both have the marelli logo stamped on them.
Yes, the QV part (124288) will directly fit the US carbed twin distributors. Interesting find about the "different" narrow rotors. AFAIK that hasn't come up here before -- can you post pics? Always possible that they increased the width before again increasing the width further on the 124288 part.
I'll end up replacing them soon. Can a set of coils that aren't quite up to the task also induce a high rpm miss? It may not be my particular issue but while I'm learning I have questions. Thanks for all your help!
I guess they could, but the 308 dual coil arrangement is much less demanding than a design using a single coil on a V8 (like most 1930-70 US cars -- although these don't go to quite such high RPM). Since each 308 coil is doing only 1/2 the work, it has more time between firing events than a single coil at the same RPM.
I have both rotors in their proper position, dwell set at 40-41 on both banks, and timing is now rock steady. The car starts and runs beautifully until close to redline when it starts to stumble. As the car reaches full operating temp the stumble occurs at progressively lower rpms. It seems heat is the variable affecting engine performance. I'm at a loss where to go next with this issue.
Some questions: 1. Same rotors or different rotors? 2. Are you saying that the RPM where the stumble occurs now is a little higher than it was before? 3. When you have the stumble occur, does the timing light still also show no spark? 4. When you have the stumble occur, does the dwell on each bank still measure OK?
The problem seemed to have cured itself.... I've noticed over the years that my car is pretty sensitive to ambient temp as it relates to air density. As the weather has cooled here in Memphis the upper rpm misfire has disappeared. I'm wondering if the plugs were getting gas fouled - less dense air making the mixture too rich. 60 idle 140 mains F36 195 AC I do experience from time to time the transition stumble so many other carbd owners have, but I find if I use more throttle the stumble goes away.
