harleym

That might be your problem. When you leave and the header heats up, the boot could be allowing the spark to jump. The more timing you add the hotter the cylinder is and could accelerate the problem also. I ran the sleeve over the wire on one engine and it caused the wire to burn badly for several inches. Removed wire, cut off damaged portion, and put it back on WITHOUT the sleeve and had no more problems. Just trying to help a neighbor as I'm located in Ocala.

travis91

Replaced the plugs with AR134 which is one heat range hotter than the old plug and did not regap from the stock .025. I contacted Autolite and they said not to regap them. Installed new Taylor wires. Checked for coil bind and have .080 clearance and reset the valve lash. The breakup is gone. Set timing at 32 and then 36 and it pulled hard all the way up through 7500 rpm. Checked that stall on the converter with the new cam and it appears to be stalling at 4500 which is 600 rpm higher than before with the old cam which stalled at 3900. I got the jetting perfect and ran a 9.87 at 137, 9.86 at 137 and a 9.79 at 139. This was in much better weather than the best run on the old cam which was a 9.87 at 137 in 66 degree weather with 80 percent humidity. Yesterday the temp was 50 with 40 percent humidity. So it doesn't look like the new cam made any performance in horsepower. I will test next time out with launch rpm and shift points to see if I find any gains there. Thanks for all the advice guys.

harleym, are you saying that you run the plug wire with no boot on the plugs that have an interference fit with the header?