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MG MGB Technical - Electronic Ignition Install

Have a '74.5 MGB GT and havd gotten my dizzy rebuilt and ready to install it and my new Flame Thrower coil...electronic ignition on rebuild (Petronics Igniter). Anything especially need to know in this process? I will be changing the spark plug wires to 7.0mm or 8.0mm. Thanks!
JW Colson

John. The only thing you need to know is that there may be some timing change when the electronic trigger is used. If possible, recruit an assistant for when you first start up the car. Hook up a timing light to the number one spark plug, have the assistant turn the engine over and use the light to determine whether you have to advance or retard the timing to get the engine started. When the car is running, you can refine the timing to the correct specification at the correct engine rpms.

Les Bengtson

How did the car run with the new rebuild?

Jeff Schlemmer

John- With the 40k Flamethrower, you might consider opening your plugs up a few k ( by the way are you running the Champion N9YC or what?).
Les or Jeff prolly have a recommendation for your enhanced capacity. Vic
vem myers


Les is correct in that timing may be off. Way off in my case when I added the petronix to my 67.
BEC Cunha

I actually did John's rebuild and recurve. When I install the pertronix, I compare it to the points and make an adjustment in the clamp position to compensate for the shifted pickup of the new trigger. Typically the Pertronix kits are 6-8 degrees advanced from the stock points position, hence the feeling of "more power" upon installation.
Jeff Schlemmer

Ever since I swapped in a Flamethrower coil
(w/ Pertronix electronic ignition) a few years ago
I've had to be extra mindful of always keeping a
spare distributor rotor in the car.

It seems that the Flamethrower's output voltage is
so great that it'll sometimes short-out the rotor through it's insulation then onto the cam spindle
- afterwhich the engine will suddenly drop dead
without any warning.

This is all done microscopically (= invisibly),
without any obvious external clues that can be
caught during routine maintenance.

I've tried using rotors from various manufacturers
(Lucas, Bosch, Borg Warner, Bap/Geon NOS, etc.).
They last about a year, or two, or so - but sooner
or later, without any warning, all of the rotors that
I've tried have succumbed to the higher voltage
and caused sudden engine death while happily
driving down the road.

Maybe it's just my sort of luck.

All said and done - I still have the Flamethrower
coil installed on my B/GT as it's really good at
making the plugs zap under most all conditions
(ie: occasional cold start fouling, heavy acceleration, etc.).

Daniel Wong

What plug gap are you using? It is the plug gap that limits HT voltage regardless of the output of the coil. Too big a gap with any coil can cause excessive HT voltage which can break down any of the HT components. Another cause if you have an after-market trigger as well as that the phasing can be way off from the original points, indicated by having to adjust the timiing significantly with the new trigger even if the distributor hasn't been out of the car. This can result in the rotor moving away from the cap contact when it fires, which results in a much bigger total gap in the HT circuit, hence a much higher HT voltage, and eventually the spark will find an easier route through the rotor or the cap than through the plugs! This knackers said rotor and cap, as well as causing weak sparking and misfiring. Centrifugal advance causes the relationship between rotor and cap to change as the timing changes, which is why the rotor contact is as wide as it is and there is an arc of burning and not just a spot, and so even though the relationship may be OK at lower revs it could be too far away at higher revs, or vice-versa.
Paul Hunt 2

This thread was discussed between 23/03/2007 and 31/03/2007

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