Slightly twitchy rev counter...

[JimB]

Hi all,

When the PI's engine is nice and hot after a long run, the idle is slightly erratic... Whilst there are all sorts of possible causes, with ignition being a prime suspect, I've noticed that the rev counter occasionally 'dips' by about 100rpm. It's like a momentary twitch! I read somewhere ages ago that since the rev counter is triggered by the low voltage/tension ignition circuit, I wonder what the cause could be?

At all other times the rev counter behaves as it should.

What do you reckon folks?

Thanks

[Alan Chatterton]

Dodgy rev counter, ignition issues mean they either work or they don't!

Eric's needs a friendly little tap to make it work....... All part of the charm!

[Mike Stevens]

The tachos work by either a current or voltage pulse, depending on age (and I can't remember which is which, late - voltage I think). It is possible that a poor points setting could cause an erratic effect.

Many years ago, I had a fault in one stromberg that made its needle valve to stick shut. That gave a very erratic tacho reading, so it's not just limited to ignition problems!

Also, as Alan says, it could easily be caused by a faulty tacho!

Cheers,
Mike.

[Steve G]

I'm not sure if it's the same problem but when the one in my car played up I stripped it apart and re-tightened some of the internal screws. Some of the screws form electrical connections between the chassis of the instrument and the terminals where the wiring joins. Over the years I think the spring washers has compressed a bit and allowed a bit of corrosion to start.