I have run my plugs at .030 gap in my points distributor in my '72 for years and never had a problem with popping up to 6000-6500 rpm. I have encountered popping with valve float(weak valve springs) and point bounce(weak point spring). I also had a problem with an intermittent pop(back through the carb) in the upper rpms on my '75 with electronic ignition due to a cheap coil wire that had burned up on the inside.
You need at least a 650dp. I run a demon 750dp and jet down. (i'm also running @ 6000ft. above sea level.) One other thing, if your running a autometer tach disconnet it there known to short @ higher rpm's
Personally I would use the factory ignition wire to power up a relay and have a wire from the battery do all the work. That way you still cut off your ignition with the key, but the power does not go all the way into the cabin, then back out to feed the system. This is not needed for the MSD box itself though, as it feeds from the battery anyway when hooked up properly. Concerning plug gap, anytime you have an electronic ignition, you should be .040" or better. Leave the narrow gaps for points. Simon, Your valves may well be floating, however I would check into richening up the carb on top end and see if that helps. When the valves float, it is not so much popping from my experience, but more like hitting a brick wall with the rpms. They reach max rpm they can handle, and then the engine falls totally flat. I suppose you could have popping if not all the springs float in unison. You might just be running out of fuel... Maybe your pump can't keep up or your floats are a touch low. My floats are a touch low right now and the car runs out of fuel faster than the stock pump can keep up around 75 mph. If the float level is right, it can be the difference between emptying the bowls or not. Dave
Right after I installed my pertronix II and flamethrower (.6 ohm) I also installed new plugs gapped to .045. And it appeared I installed a popper with it, because above 4000 rpms it just backfired like crazy. My fix was easy, I crossed the plug wires for #2 and #3. I am running a bone stock 302 with a Holley Contender intake and Holley Street Avenger Vacuum seconday 670, 2.25 inch dual exhaust with balance pipe. Will turn 5500 any day with out backfiring at all or floating the valves. rk
i am running a 3/8" aluminum fuel line all the way and an edelbrock mechanical fuel pump that i got from scooper. the fuel system is completely restored. my carb was rich at one point and it ran worse. so its back to stock with 2 steps up on the springs in the carb. it runs good there.. i am going to get it dyno'd.. i called the dyno place the other day. $65 for a base line test, and $110 an hour to tune it. i may spend $65 to get it baselined.. and then when i get all the goodies on it, i will spend the $110 for the tune session and get it dialed in
Just thought I'd update, turned out to be my carb spacer gaskets leaking, top and bottom. Took the (synthetic) spacer out, put a new gasket in, and it runs like a champ to 6,000rpm.
