What's a real good arm for a Decca Cartridge?

+1 bdp24
There is nothing wrong with your arm. It is the cartridge, just one of the things you have to live with when you get a Decca. They can sound great but they do not track so hot. Just like any British sports car.  Most people I know with Deccas have other cartridges they can use on tougher disc. Instead of getting a new arm jest get another cartridge!

Mike

Poppycock! My Decca SG tracks perfectly in my 12" Jelco 850L at 1.65g. I have a Decca Grey Garrott Export in a 12" 750L and it too tracks perfectly at 1.7g.
I do use heavy mounting bolts (brass) on the headshell.

Touche', @noromance. What I should have said is that if you have a Decca (is the op's a Decca, or a London?) in an SME, and you have mistracking, I would suspect the cartridge before the arm. Not all Deccas mistrack, but they are well known to not be the best tracking pickups around. The best examples are fine, others not so much. I never managed to get a hold of a Garrotted-version; I tried to pry one out of Ken Kessler's hands, but he wouldn't budge ;-) .

The modern London cartridges made by John Wright have much better quality control than the original Decca Special Products output (which was indeed a bit of a lottery).
I have had Decca for 40 years now, and they will track most records. No they won't do the cannons on the Telarc 1812 Overture, but very few cartridges will track that.
Traditionally they were best mated to damped unipivots. The lack of vertical compliance meant that the vertical vector energy could be dissipated in the unipivot without affecting the cartridge performance. I've used my Maroon, Garrott Bros Gold and FFSS MkIV C4E (John Wright rebuilt with fine line tip) in my Hadcock 228 and Schroeder tonearms (Model 2 carbon and Reference) with great results.

Even the very best examples have trouble with the heaviest passages. Just get an Ortofon test disc and try out the vertical tracking band. I have done this with the London Reference and it could not do it. 
It is however a wonderful sounding cartridge and many people do not have that many albums that are that difficult. If you are a Metal fan and like Telarc's 1812 Overature you would be better off with a different cartridge. Decca cartridges are also notoriously unreliable. Perhaps there is a problem with dhcod's example but unless he hit the bearing assembly of the SME with a hammer it is unlikely to be the source of the problem. The SME can be set up for any mid to low compliance cartridge by adding enough mass hopefully using a test record to check the results. Oh, I happen to like Poppycock.