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This has stumped me. My Tachometer was working fine before the engine rebuild and has since decided to tell me the engine is turning twice as fast as it is. Nothing in the wiring has changed or even been disturbed. Has anyone any bright ideas or is just that it’s de died to play awkward?

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Smiths back in the day Tachos do not like electronic ign; in my experience ,, so if you are still using conventional Points bin this suggestion.
otherwise Speedy Cables have repaired mine .

Points or electronic? If points, it could be condenser failure, or try cleaning the contact faces with emery.

Also check you have the + and - wires correctly on the coil, else the HT return path will be via the RVI loop instead of the condenser, causing a double pulse.

Still on points. I checked and double checked the coil connections, not that. Reworking the points this morning made no difference. I’ll swap out the condenser but I can’t be sure that any replacement is any better. I must get a remote condenser set up if only as a means of eliminating a duff standard one when trouble shooting. Useful to have in the in car spares box.

The hunt continues.

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Is it possible it’s become set for a different number of cylinders? If it’s reading exactly double it might be set for 2 cylinders (or should that be 8?)

finchy533 wrote: ↑Sat Aug 22, 2020 5:35 pm Is it possible it’s become set for a different number of cylinders? If it’s reading exactly double it might be set for 2 cylinders (or should that be 8?)

The Tachometer has not been disturbed nor has it wiring. Still a puzzle.

D

Try turning the fitting on the back, with the loop of wire, through 180 degrees. I have no theory for this. Just grasping at straws.

The nylon fitting on the back of the Tacho that the white wires loop through will only fit one way due to the offset hole that locates this item so rotation as suggested is not possible,

Try taking one of the loops out of the white wire at the back of the tsch if all else fails.

Yeah i had to lose a loop to make mine work...it was still exponentially out a bit though...i did make the loop smaller and it helped a bit as the current sensing is very 'sensitive'. Lol.

I bought the new board from Spidya that converts the board to a modern style. Fixed the problem, allows electronic ignition, and still says, RVI on the tach face to keep the purists happy.

For my other car I just bought a RVC for cheap, it works much better and is much easier to install imo.

Cheers!