Cartridge / arm combination.How do you know?

Mistracking springs to mind. But to say that it incorrect has to be divided into two questions. The first being : is the arm and cartridge physically suited for each other. This involves matching the compliance of the cartridge to the mass of the arm. Also you probably would not want to put a $5000 cartridge in a cheap arm, the bearings in the arm would not do the cartridge justice. The second question would be "I don't think this arm and cartridge is giving me the sound I expected". Outside of audible mistracking this is a much harder question because most of it involves not what you hear but what you don't hear. There is a failure to resolve detail and to follow the pace and rhythm of the music. Like the Supreme Court Justice you may not be able to describe it but you will know it when you hear it. If you feel that yours is not working properly the best thing is to have it checked by a competent set up person IF you can find one.

I am suspecting my arm may be too light.My setup is a Pro-ject 2.9 wood with a carbonfiber arm and a AT-150mlx.I have played with and adjusted most everything numerous times.Sounds good but my Kyocera with an AT-14sa seem to better it.Would you think the original metal arm may be better suited or do you have some economical suggestions?

The carbon fiber arms were generally aimed at a generation of cartridges that are extinct, ones with compliance of 40 or 50. But yours may be of newer design. Try to find out the mass of the arm and compare it with the compliance of the cartridge. There are formulas, which I don't have off the top of my head, to determine compatibility. If the metal arm has more mass it would be worth trying. For a new arm Rega is the almost universal recommendation in the under $800 range.

It is also possible to add mass to a tonearm. Some cartridges use to come with a lead weight to add mass. You could try adding some Blutak or similar substance to the headshell in moderation, look at sites like vinyl engine for advice on this.