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MG MGB Technical - tachometer

just took the mgb for a ride after installing the new dist. It called for the 12v at the coil with no resistors and i had to disconnect anything that would cause it to run on resistor. In doing so I have stopped the tach from working and when i pull out the key the engine runs for a few seconds. I think the running of engine is a timing issue and will use a strob to set it. Its the wire working the tach that I need to reinstall without screwing up the new dist. Any thoughts or advice welcomed ,thanks , Doug
dd doug46chief

A bit more detail about the setup you have would help. Is it an electronic dissi? Not sure what they mean about resistor, is this to ground from the sw terminal? The transformer coupled style of tacho would work fine here, the igintion LT cant see it as a DC load.
Stan Best

STAN, patronix electronic dist and matching coil, the coil needs direct 12v when the ignition is turned on. Any thing like the wires that stay hot with igniton off are eliminated from the coil and tied up. tomorrow i will post some pics of my set up. DOUG
dd doug46chief

Doug. The wire from the negative terminal of the coil to the tach needs to remain connected. Should be one of the two white/blue wires that were removed from the original coil.

Les
Les Bengtson

What year is your car?
Dave O'Neill2

Les thanks i will try that today,that would seem logical as the other wire set went to pos and it was hot all the time. Dave year is a 79,thanks ,Doug
dd doug46chief

Black/white goes between coil -ve, distributor and tach, not white/blue. With Petronix the black wire from that replaces the one between coil and distributor, but the other one is for the tach and needs to remain connected.

What type of running-on do you have - the rocking and shuddering Dieselling type, or normal running?

American spec cars from 1973 had an anti-runon valve, which was intimately involved with the emissions plumbing. If almost anything of that is blocked, leaking or disconnected it will disable the functioning of the valve, which could cause Dieselling.

From 1977 with the ignition relay (one of two by the fusebox) there was a wiring design fault that meant that if the anti-runon valve doesn't do its job for any reason, the car engine will continue to run normally for a few seconds after the ignition is turned off.
PaulH Solihull

This thread was discussed between 12/02/2012 and 14/02/2012

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