Pertronix & Mallory Vac Advance

[Russ-Notts]

Hi,
Previously I had a Mallory dual point distributor on my Rover v8 with a Lucas Sport coil. The distributor has a vacuum advance module which is connected to the ported vacuum on my Holley carb. All worked fine.
I decided to ditch the points and replace with a Pertronix Ignitor and flamethrower coil. I set the timing as normal using a strobe light with the vacuum line to the module disconnected and plugged. Timing at idle is around 7 degrees BTDC. All good so far. Reconnected the vacuum line to the advance module and then above 1500+ rpm the engine starts backfiring. Disconnecting the vac advance and it revs up okay.
The vacuum advance has not been touched in any way from how it was set before with the points. A vacuum gauge on the ported vacuum on my Holley reads around 10-15Hg at idle and goes up as the revs climb. (although I didn't rev it up too high)
Any ideas why the vac advance setup worked before but causes problems now the Pertronix is fitted? What's the fix?
Cheers,

[wilf]

Maybe the drag of the points was restricting the amount of vac advance. Try checking with your strobe to see what is happening.

You don't need it anyway, so to make the car driveable again, disconnect it.

[David Large]

Is the rotor arm ok and is it the right one? Did you change it?

DL

[Orange Cobra]

Howdy

I have changed to Pertronix on my 351.Although I have mechanical advance I had a similar issue and after checking found that I had connected the Petronix electrical positive behind my ballast resistor so it was only getting around 9 volts where as it should have been getting 12 volts. Works fine now, doh.

"Q. How to correct a low voltage problem?
A. First, if you have an external ballast resistor, connect the red Ignitor™ wire to the ignition wire prior to the ballast resistor. Second, if you do not have a ballast resistor you must locate a 12 volt source that is controlled by the ignition switch to connect the red Ignitor™ wire to."

Regards

Frank

[Purple AK]

Russ. I'm not sure you should be seeing any vac at the timed port at tickover? I could be wrong.

[Russ-Notts]

All,
Thanks for the replies. You've given me a few things to check. I'll certainly go back and confirm the carb vacuum on idle. It does seem high and maybe the throttle butterflies are not closing correctly? As Wilf has suggested, the vac advance may have never been able to advance the points and hence now moving freely the setup is giving too much advance. I believe the Mallory vacuum can is adjustable by rotating it?
I did change the rotor arm for the one supplied with my Pertronix kit. It looked like the same Mallory rotor that was fitted with my original points setup. (I have the old one, I'll confirm they are the same size.) The dissy cap is the original. When I fitted the Ignitor I couldn't find a ballast resistor and the voltage at the coil was around 12v. (I can make a quick check on this).

Cheers,
Russ.