Backfire or Afterfire ?

[asolde]

1969 chevy 350,overhauled quadrajet carb,new pertronix ignition system. I will get up to speed around 55mph. Then all of the sudden a loss of power and POW! I believe out the exhuast and then picks up and gose like normal. Dosen't do it all the time just when I get on the highway. Runs good at all other conditions.

I have the carb mount directly to the cast iron manifold with a stainless steel shim, then a gasket then the carb. I have a divorced choke set up. Idle is set to spec.The ignition system is a pertronix set to spec.

Any Ideas?

['68OrangeSunshine]

Pertronix Ignitor, Ignitor II or III? Flame-Thrower [I, II or III] Coil?
Did you run a new 10 or 12 ga. power lead from the tap in the Fuse block to the distributor (+), bypassing the stock Yellow 20 ga line? If not when the Yellow 20/Orange/Purple/White wire heats up, its resistance increases, dropping voltage down to 9VDC from 12VDC.

[asolde]

Originally Posted by '68OrangeSunshine

Pertronix Ignitor, Ignitor II or III? Flame-Thrower [I, II or III] Coil?
Did you run a new 10 or 12 ga. power lead from the tap in the Fuse block to the distributor (+), bypassing the stock Yellow 20 ga line? If not when the Yellow 20/Orange/Purple/White wire heats up, its resistance increases, dropping voltage down to 9VDC from 12VDC.

I am running pertronix ignitor III and flame thower coil 40000 volt. But yes I did run the yellow 20 ga to the positive side of the coil. So then I should run a 12 ga wire from the fuse block that is hot when the key is turned on? What do I do with the yellow wire just tape it off?

['68OrangeSunshine]

Originally Posted by asolde

I am running pertronix ignitor III and flame thower coil 40000 volt. But yes I did run the yellow 20 ga to the positive side of the coil. So then I should run a 12 ga wire from the fuse block that is hot when the key is turned on? What do I do with the yellow wire just tape it off?

Yes. A separate wire 10 or 12 gauge wire [Red looks good] from a tap ''IGN UNFUSED'' on the fuse block, thru the firewall to the coil positive terminal. [HOT with the key ON.] You could put a fuse in it -- I didn't. Tape off the old yellow wires, in case you want to go back to points, like in an emergency. I never had a problem with my Pertronix Ignitor II, in 5 years.
Today I did accidently kick my Red 10 ga. lead off the terminal in traffic to the HEI for the 350 V8 in '71 GMC Jimmy. I dead-sticked off the road and after 5 minutes troubleshooting found the gremlin and reconnected it. Good to go. A little more pressure with some needlenose pliers and it won't happen again.
Some people hard wire them. I treat it like a truck, not a Boeing 777.

[asolde]

Update I ran the 12 ga red wire from the fuse blk to my coil and it was a good soild fix. Thxs Alex

[hamjet]

X2, sounds like you're loosing spark for a milisecond and when it catches again its burning the unignited gas, back in the day we would reach over and turn the ignition key off and back on to whom ever was driving, one time we held it too long and it split his muffler wide open...

[GMCJOE]

Sound like your carb couldbr overloading, running a bit rich. I had one doing that a few years back.

[hamjet]

http://67-72chevytrucks.com/vboard/s...d.php?t=148346 Read this...

['68OrangeSunshine]

Cool, Brother.
Glad to be of help.