Old School VDO Tach - RPM reading low?

[Deanodynosaurs]

I've got a 6'000 RPM VDO tach and when I wired it up to my van (t25 but I dont think that will make a difference, eventually going in my 12v bug) I found that although it works, the actuall reading is really low, about half the rpm it should be?  It does go up and down with the engine RPM though.

It deffo a 12v unit, and on the back it has the following codes etc

230/13/10

    12v

24000

I wired it up with a 12v feed to the '12v' post, the negative side of the coil to the '1' post, and earthed the '-' post.

Any ideas whats up with it? Do i need some sort of intermediate unit?

For refrence it will be used with a MSD system with a reading taken off the blaster coil, although tested on stock t25 coil.

Cheers in advance.

Dude 

[TexasTom]

Probably a good chance the original application was for a 6 or 8 cylinder engine.
You'd likely have to send it to an experienced VDO Tech, perhaps they could modify it for four cyl. use?
Good luck with it ...
TxT

[Deanodynosaurs]

Probably a good chance the original application was for a 6 or 8 cylinder engine.
You'd likely have to send it to an experienced VDO Tech, perhaps they could modify it for four cyl. use?
Good luck with it ...
TxT

  Great, when i brought it i was told it was a 4 cylinder tacho, and thought it was as face design is same as a early beetle speedo.

I'll have to try and see if somebody can modify it...........

Cheers for the info anyway.

Dude 

[Flow]

It's the problem I have with my tach too... (not a VDO) and somebody told me it was used with a 6 cylinder engine