Need help on new cassette install
 

I have been riding for about 18 months, the bike I have has a 11-23 cassette. I have just installed 11-28, I notice a "feeling" in my pedals. I have not changed any thing on my chain etc. any suggestions an what I need to do.

Maybe you need to add 4 half links or so to the chain (or get a new chain if you don't have the links) and break it so it's longer than before, and make a slight adjustment to the B-screw to have the correct distance below the cogs averaged over 11-28 cluster as opposed to the previous one.

How many miles were on the old cassette/chain.

Likely you need a longer chain (look up how to figure out chain length - it's very easy and only takes a couple seconds.) You may also need a new chain if your old one is significantly worn. I would take off the old chain and put it in a bag with the 11-23 cassette and get a new chain for your new cassette.

Thanks sounds like good advice, will do

Put a bit of tension on the chain and a 12" ruler against it. If 12 pairs of links are more than 1/16" over 12", the chain needs replacement. If it's more than 1/8" over, it chews cogs pretty hard.

But even if it's only a little worn it'll accelerate wear on the cassette. You can get more life out of a cassette by getting two or three chains at the same time as the cassette and rotating them every 1000km or so.