Elan S4 Rev Counter Over Reading

[RAJ2628]

Hi, I am near the end of my Elan S4 FHC rebuild but I have a Rev Counter issue which I am hoping the forum can help me with.
During the rebuild I sent my Rev Counter and Speedo for refurbishment.
I run mechanical points and, whilst I am not interested in electronic conversion at this stage, the rev counter is modified to accept that change in the future.
2 weeks ago my vastly Elan experienced auto electrican wired in the rev counter and it registered nothing. Returned it to the refurbishers and they said there was a fault, fixed it and checked it through the rev range. All OK. The Rev Counter was wired in for the 2nd time and it worked, but at tick over (800- 1000rpm) it read around 4000 rpm. With the refurbishers guidance, the speedo was adjusted so that it read 1000rpm but when we increased it up to about 4000rpm the gauge only moved another 500rpm. Bummer.
My set up.
New, alternator version, harness from Auto Sparks. New Dynalite Alternator from Holdens
Reconditioned mechanical distributor by Distributor Doctor. All new electrical parts supplied by him.
New bog standard non ballasted coil from SJS.
Eurocarb supplied new Facet fuel pump in boot.
Earth and power connections good.
Also tried it by wiring it separately from the harness. The pulse cable from the negative coil side to the rev counter is a separate cable within a flexible plastic conduit.
All components, especially condenser, coil, alternator snd wiring purchased from reputable sources.
No fleabay/dodgy suppliers.
What can be causing this 4/5 times over reading error at tick over.
All sensible thoughts welcome.
I have arranged in a couple of days time to try it on another Elan to see if the fault is the gauge or my wiring or faulty components (coil, condenser, signal tracking etc.)
Al

[mbell]

I run mechanical points and, whilst I am not interested in electronic conversion at this stage, the rev counter is modified to accept that change in the future.

Are you able to be a bit more specific on this?

I've converted mine and adjusted it but really even converted they aren't very accurate and the calibration is really picking the spot where you want it to be most accurate, with rest of range likely be off.

Basically sounds like you need to calibrate it on the vehicle to try find a suitable calibration point.

[Craven]

“I run mechanical points and, whilst I am not interested in electronic conversion at this stage, the rev counter is modified to accept that change in the future”
This sounds as if you have non-standard circuit now, the electronic pulses that drive the rev counter are very different when produce by a points system. So possible that your new circuit may be having trouble
dealing with an old ignition system

[Craven]

“I run mechanical points and, whilst I am not interested in electronic conversion at this stage, the rev counter is modified to accept that change in the future”
This sounds as if you have non-standard circuit now, the electronic pulses that drive the rev counter are very different when produce by a points system. So possible that your new circuit may be having trouble
dealing with an old ignition system

[gjz30075]

Could they have refurbished your tach for a 6 or 8 cylinder? I have a tachometer, used for diagnostic
purposes, that has a slider switch to go between 4.6 or 8 cylinders and if I don't check the switch and it happens to be on 8 cylinders, it'll read like yours.

[nmauduit]

Could they have refurbished your tach for a 6 or 8 cylinder? I have a tachometer, used for diagnostic
purposes, that has a slider switch to go between 4.6 or 8 cylinders and if I don't check the switch and it happens to be on 8 cylinders, it'll read like yours.

I suppose that if that was the case an underreading would be observed rather.

[RAJ2628]

I run mechanical points and, whilst I am not interested in electronic conversion at this stage, the rev counter is modified to accept that change in the future.

Are you able to be a bit more specific on this?

I've converted mine and adjusted it but really even converted they aren't very accurate and the calibration is really picking the spot where you want it to be most accurate, with rest of range likely be off.

Basically sounds like you need to calibrate it on the vehicle to try find a suitable calibration point.

The Tacho is set up for points through a dual connection, I was told. I'm not looking for it to read to with a few revs, but registering 4000rpm when it should be 1000rpm is a bit too much.
As I said we did recalibrate it on the car and managed to get the tacho to read 1000rpm at idle. However when we then increased the engine revs the gauge could only measure 500 of the increase (about 4000rpm)

[David1953]

I had a similar problem with my tacho, I think the electronic module the refurbisher used was not happy with points.
I ended up sending it to speedy cables who were not very complementary about the previous work and I have had no problems since.