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MG MGB Technical - electric tacho bits

I am looking for the coil and holder that mount on the rear of the electric tacho. Does anyone have one to offer?

Dominic Clancy

Are you talking about the RVI pickup loop & fitting?

If so the loop is part of the wiring loom and the little brass U, plastic spacer and nut are the first things to disappear into oblivion when you disassemble the car!

I'll have a rake round and see if I can find a set - but tbh most of the RVI units get binned cos they don't work with electronic ignition.
Chris at Octarine Services

Hi Chris

Yes, that's the bit. The car (a midget) is staying standard points so no probe with electronic ignition.

Peter is doing the head at the moment

Dominic Clancy

"RVI units get binned cos they don't work with electronic ignition"

The trick with that is to power the electronic ignition from the white at the fusebox, not the white at the coil that is usually shown on the fitting instructions.
Paul Hunt

No Paul - that trick doesn't always work. The pulse from the coil is often too weak to consistently fire the RVI tacho when using electronic systems.

I won't even take the chance with customer's cars - I don't like getting returned cars with complaints!

Chris at Octarine Services

I have just fitted an Accuspark ignition to my car (have not had it running yet).
Also my Rev counter is not a coil type it has just two connections, one is a bullet the other a spade,What type is this?? and will it interfere with the ignition.??
Your comments please.

GJ Barker


Bullet & spade is the RVC (look on the face of the tacho below the needle) type which is voltage sensing and will work OK with electronic units.
Chris at Octarine Services

The pulse is too weak? What effect does that have on the spark!? However it's not generally known that inductive electronic ignition systems, including the under-cap type, do result in a reduced current through the coil. That's why the factory fitted low-resistance coils to American spec cars when electronic ignition became standard.

The usual complaint I've seen is that RVI tachs read double with many different types of electronic ignition, and originally the 'cure for that is to alter the pickup so the wire only makes one pass though i.e. half as turn, instead of the original full turn i.e. two passes. But using a different source is easier, and certainly both are worth trying rather than binning it.

My Sparkrite system in the 70s came with a tach adapter, but I didn't have a tach. And I didn't find it made a worth-while difference anyway so I took it off when selling that car and never bothered fitting it again, it's still in a garage drawer.
Paul Hunt

This thread was discussed between 11/02/2014 and 13/02/2014

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