Important plug gap question

[66StangGuy]

Problem: When secondaries open car stumbles. This only occures when secondaries open while in gear or when reving in park. when in park secondaries open fine and primaries fine. only when i open both at the same time the motor boggs. The last thing i did on the car before the problem is this. Installed new cap and rotor, New MSD 8.5mm cut to fit custom plug wires, new motorcraft resistor sparkplugs. stock heat range. Also running msd coil. used to have the box too but it took a crap on me. i also set the plug gap pretty high. i know my coil can make the gap no problem and it starts and runs great. only problem is when i give it a lot of fuel and air it seems to miss 2 cylinders then fire maybe 2 and then miss 3 or something like that in no certain order. if i leave the pedal there and see if it will recover it does not untill i back off the pedal enough to close the secondaries. only thing i can think of is that the compression (about 9.0:1) is preventing the spark or the spark is not sufficient.

does this make any sense? any other ideas to try and find whats wrong. iv already ruled out the carb. its a new holley 600cfm vac sec. no vaccume leaks or anything abnormal.. it all runs great untill the secondaries open. but if i open the secondaries by themselves under the hood the motor revs fine no problem. power valve is assumed to be good because of this. what am i missing here guys?

[mustangman65_79]

I was reading up on vac sec when I got my 600 CFM holley, I found out that if the motor stumbles when the secs open, that it is too much gas, and basicly your flooding your motor out. Your secs shouldn't open when the car is in park, or netrual, only when moving. I found all this out when I thought my car had the same prob, just to later found out I just had a really bad vac leak.

U should be running a gap of .35 stock coil, max of .45 on a aftermarket coil. I run a .40 gap on my 302 with a 45,000 volt coil and 750 holley vac sec.

[matt1190]

mustang man is correct. Your vacuum secondaries should not open when the vehicle isn't moving (isn't under load). So, if the car is bogging in Park and its rich, just imagine how rich it is on the street when you actually open up the secondaries. Good luck

[66StangGuy]

i know the secondaries arent supposed to open in park. also its not running rich. its just that when the secondaries open with the primaries the motor boggs. just saying that i can control the secondaires and open them fine. so i know its not a bad powervalve or secondaries diaphram. thats why i though it might be spark plug gap.

[hobgoblin351]

Just my 2cents but it sounds to me like your accelerator pump. When you go WOT you're engine is running lean and needs a shot of fuel to carry it until the secondary circuit becomes active. The "bog" everyone feels is not always the engine choking on too much gas. It actually needs more fuel to compensate for the secondary barrels being open and flowing more air.

[66StangGuy]

i found my problem the other day.i reset the gap on my spark plug back to stock and reset the primary and secondairy floats and the problem dissapeared. i put a new valve cover gasket on as well that i needed. anyway thanks for the ideas and for stickin with me. im just glad i could get it to run at all so i could get to school. thanks again.