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Recently acquired a '72 B50MX project and am in need of advice on which type of ignition I have. Engine is rebuilt and in the frame with leads for points and alternator as expected. There is no other wiring provided but in a box with the bike I received a coil, capacitor, zener, rectifier and condenser. My shop manual shows diagrams for both capacitor and energy transfer types of ignition. Can someone please advise on how to tell which I should have? The seller was not positive the box of ignition parts he gave me was from this bike : )

Thanks and I apologize if this thread exists elsewhere- I looked around.

Jack
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Ex works it was ET ignition with a cut down alternator with just 2 coils. Most were converted to full alternator, 2mc capacitor zener. Look at your auto advance unit, ET will be 5 degrees, non ET will be 12 degrees cam advance. Advance at crank is double the cam advance, kick back on starting is much less likely with 12 degrees advance at the cam.

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what type of stator do you have ?
It's probably a lot easier to rectify the stator output
and run a batteryless dc ignition ( big blue capacitor )
than mess with the ET ignition .
( though if you have good ET components it can be reliable )... it has its fans .

The ET system was all AC
the ET ignition uses a 4 or 5 wire stator .
a 5th wire is grounded , if used with a single cylinder .
the correct two wires run the ignition , the other two wires run AC lighting .

( there is another type stator that a B50mx could have run )
... that only has the ignition coils . its a cut down 1/3 round stator
... look Ma , no lights , I'm a badass MX machine
[Linked Image from bsab50mxrebuild.weebly.com]

all these ET stators were paired with a smaller ( lower ohm ) remote coil .
and The ET ignition also needs ... a special ET points cam profile

If you have a rectifier and a zener ... its probably not ET , and has been modified like many , at some point .
and you can use what you have ... or start over and pick your poison .

Last edited by quinten; 06/18/22 9:04 pm.
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ETS (energy transfer system) can be a real pain in the butt if not set up perfectly. I doubt you have that. They went away in 67. The coil for the ETS is very different from a standard coil and runs on a/c current from the alternator. I’d go with a Boyer ignition, Podtronics regulator. Then you can toss out the rectifier and zener.

Last edited by Roadwarrior; 06/19/22 3:05 am.

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Originally Posted by Roadwarrior
They went away in 67.
Not quite true. ET ignitions (which I can't ever remember seeing referred to as ETS), went away from road bikes in 1967 because of a law in the U.S. went into effect that required brake lights to operate independent of the engine. Off-road bikes were different, and the B50MX was equipped with an ET ignition system that had, as mentioned by someone else, a cut-down stator that only had the ignition coils on it in order to save weight.

The ET is a fine system, but anyone with an ET system should read this thread.


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