Smiths impulse tach reading high

[65Austin]

I have an RVI impulse tach that reads about 2000 too high, do I adjust this by moving the pulse lead "loop" at the head? or would making the leads longer before they attach to the coil work? or is it knackered?

just bought this used, and the pulse leads are about 24" long. how long should they be from new? the part where the lead loops through the tach appears to be untouched and perhaps in the original place?

thanks...

[ivor badger]

They always do, probably because they set them off the mains cycles. Look on the back and you will see a small flat rubber plug, remove it and you will see a white plastic screw head underneath with a screw driver slot in the top. This is the calibration adjuster. Iirc, the revs are correct at 3000rpm

You need to find a suitably calibrated tach to read the revs near full speed. Run the engine up to near max revs and turn the screw until the revs read correctly at the chosen speed. It's probably wrong at low revs, but that doesn't really matter.

[mini129]

Are you using electronic ignition?

[mk1]

As Ivor says, these tachos are notoriously badly calibrated and are more of a fashion statement than serious instrument to monitor your engine.

If you do want an accurate measure of your engine revs. my suggestion would be to buy a decent one.

[65Austin]

thanks for the info...

ivor - will give the adjustment a try

mini129 - regular ignition, MK1 998 cooper

mk1 - fashion statement, just need to find a good used pod for it

[mk1]

I probably came over a bit grumpy in my previous post. This wasn't deliberate, I use these old tachos. in a few of my Minis & am very happy with them. But when I need a tacho to be accurate I buy a new one.

Pods are available from the shop;

http://mk1-performance-conversions.co.uk/shop/

PS. I have about 10 left & this will be the last batch I do.