August edition - High-RPM Misfire - Suggested MSD Updates:

If you are using a MSD ignition system we strongly suggest you install the updated #8862 shielded magnetic pickup harness which connects the distributor to the ignition box. This shielded harness which includes a ground wire, greatly reduces the possiblity of induced voltage to the trigger circuit.

It is also suggested by MSD to twist the magnetic pickup wires coming out of the distributor or your pickup on your crank trigger to reduce outside voltage (RF) that can mistrigger your ignition. Install the distributor pickup harness as far away as possible from any wires, especially the primary coil wires and sparkplug wires.

We also suggest installing the MSD #8830 RF filter in the constant power supply wire and ground when using a MSD ignition box to filter any unstable voltage to your MSD Two-Step rev control or other electronic accessories.

These two inexpensive "fixes" cured a misfire gremlin that plagued us (and showed up in the tach at high rpms) when we increased the battery voltage in our '57 Chev. We were only able to locate the problem using a lab scope to detect stray voltage near the distributor pickup wires! This common problem was also confirmed after a frustrating weekend, by the MSD tech department.

Another problem you may run into is fuel siphon from the accelerator pump. At high rpm the nozzle may “flutter” causing fuel to leak by and leading to a high rpm misfire. This concern can cause some issues in tuning the carb. To check for this concern first remove the air cleaner assembly, start and warm up the engine, hold engine at race rpm and look down the barrels (MAKE SURE THAT YOU ARE WEARING SAFETY GLASSES WHEN YOU DO THIS) to see if the nozzle is dripping/spraying fuel into the engine. If it is then you can start by lowering the float level slightly or tightening the acceleration spring or even compensating for this issue by reducing the main jet size.

I have been chasing a high(er) RPM "false rev limiter" on two cars with MSD 6AL's for the last few months. One is a 69 Charger with a 528 Hemi and the other a 69 Super Bee with a 440 in it. After a lot of work and chasing shadows for way too long, I think that I, with the help of MSD, have found a solution. It seems as though many of the newer MSD pieces are very sensitive to RFI and EMI interference. Here are a couple of things to check and do:

1. When you installed your MSD, did you cut the approproate wires to length or did you coil them up and tuck them out of the way? If they are coiled upon themselves, this can be a source if interference, especially under load.

2. When you intalled your MSD, did you run any of the signal or trigger wires along any 12 volt power wires, near a plug wire, the alternator, or the coil? This too can cause interference (although most everyone avoids these issues).

If the installation seems "text book" and you avoided any installation pitfalls, the next step is to go with a sheilding kit. I know, I have run MSD's for twenty years as well, and I never needed a shielding kit either. It seems as if one or two things have changed (although MSD won't admit to either) - the 6's are more vulnerable to interference than in the past (possibly due to a change in shielding of the electrical wires) or the shielding on the 8.5's is not as efficient as it was in the past. These are my inferences (for what they are worth). I believe that MSD now makes a shielding kit (from what they told me on the phone yesterday) or you can go to Radio Shack and buy grounded electrical wire shielding. That should help.

Worth a try.