I just changed my cassette from a 32 to a 34. All is good but on the big sprocket in the front it will not change properly on the big sprocket on the rear. On the small sprocket on the front it will shift good onto the big big sprocket on the rear. What am I missing? Adjustment or a longer chain?
If you can change to biggest sprocket on the small chainring, sounds like the chain is too short. If it's new you can add a link in (if you have the left over links), otherwise you'll need to replace and resize the chain.
You should probably also check that your rear derailleur can take a 34 tooth max cassette sprocket, and you have not exceeded the derailleur total capacity (difference in chainring tooth counts plus difference between largest and smallest sprocket tooth counts).