Tach reading about 1200 rpm high across the board?

[angelo78]

Hi guys,

Just installed a msd tach adaptor to get my factory ralley tach to work with my msd 6a .  Only problem is that it reads about 1200 rpm high across the entire rev range.  Could a faulty resister cause this and could I ad an inline resister?  Anyone got any Other ideas?

Cheers

[HP_Cuda]

Are you attaching it to the grey wire?

[angelo78]

Yes Mate, Grey wire.

[dodj]

Did you install the 8290 adapter? Was the tach accurate before the MSD ign? Factory tachs are not noted for their accuracy

[angelo78]

Hi Dodj,

Yeah sure it is the 8290 adaptor.

Since I got the car the I have not had the Tacho working until now, so don't really have a baseline to go off. 

[dodj]

I plan on installing one of these eventually.
http://rt-eng.com/rte/index.php/RTE_67-74_Tach_kit

If you read the write-up under 'detailed information' it mentions a potentiometer on the original cct board. So it is probably adjustable.
In my mind though, if I have the tach that far apart, might as well put a new board in rather than adjusting the old. 

[angelo78]

Wish i saw that before i bought the tach adaptor.

[dodj]

You and me both. New board is not much more than the adapter. 

[angelo78]

Update,

Removed the Tacho,  the wave washers behind 2 of the springs had a bit of corrosion on them which effected the alighnment of the shaft to the needle and created a restriction at about the 1500 rpm indicating mark.  I cleaned them up and now have the 0 to 2000 rpm reading correct. It is now 1000 rpm out at the top scale reads 6k when its only 5k.  There seem to be the ability to adjust the return springs so i will have another go tonight.

Cheers

[angelo78]

Latest update is i adjusted the pot on the factory board and it is now spot on through the entire range.  Was a lot of trial and error but worth the effort👍

[dodj]