I'd like to add that I gave my car a good thrashing on the way to work, need to thicken the carby oil slightely. But it went well, I went to just over 6000 in first, no wheelspin (I took off slowly then gunned it). It was fun and the tacho kept up, oh and the dunlop grip nice. But when I shifted into 2nd then 3rd it went dodgy..again...

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1964 Morris 850, 1330 Supercharged - 81.8hp atws.
1975 Leyland Mini S 1100S powered - Nice and reliable.
1977 Leyland Mini LS - Project LS-T

What ignition are you running?
Sometimes the tacho will do silly things if the points are bouncing or shagged.

pulsar for both minis.

I reckon it's got a lot to do with my printed circuit board and my wiring might be shorting itself a bit somewhere.

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1964 Morris 850, 1330 Supercharged - 81.8hp atws.
1975 Leyland Mini S 1100S powered - Nice and reliable.
1977 Leyland Mini LS - Project LS-T

i have a simular problem, found a couple of dry joints which needed re soldereing.

I have another tach from an aussie 1275gt which i cannot get to work. The IC in it is stuffed no pulse signal. But i have never been able to figure out what the IC is to replace it.

Must instances is the Ic just gives up or the pulse signal starts to break down hence the needle swings over the place.

ICs have numbers on it small black rectangle with eight silver pins sticking out of it.

a circuit diagram would make to a hec of lot easier to fix them, any one got one

Cheers

kiwiinwgtn