Tachometer gone mad

[Mike Wattam <101714.1343@domain.elided>]

A member of the TSR (not me) has a weird problem - can you sparkies out
there help with this?

He has had Lumenition on his otherwise standard Stag for many years, but
just as they all go, when the motor got hot this year the module stops
working until it cools down again.  He has spent a lot of time in lay-bys -
whatever turns you on.

So, on with a replacement ignition kit, this time Piranha (what Rimmer Bros
now supply).  The rev-counter is now erratic, being OK at low revs but over
3,000 starts falling back until at actual 5,000 it reads erratically less
than 2,000rpm!

So, change the distributor for a lovely old-fashioned points unit form a
donor car, rev-counter is now fine.  Fit the 'Piranha' distributor on the
'other' Stag, on which the rev-counter now works fine. Fit my friends'
rev-counter on the donor car, rev-counter STILL works fine.  Very funny,
very very funny.

Take the Piranha distributor and rev-counter off the donor car and refit
both to my friends' car, and the donor car rev-counter works fine.

Conclusion is the Piranha distributor will work with one rev-counter but
not the other, my firends car, although Piranha distributor works well with
either rev-counter on both cars.  Both the rev-counters are identical
models and ages.  Can anybody suggest any reasons?

I am going to visit my friend in the lunatic assylum on Sunday, and would
like to give him your views.  Assuming he hasn't escaped to Korea.

Mike Wattam
Triumph Stag Register