Here's a pictorial on how I did up my CRF250R seat for long trail rides in the mountains. The stock seats in recent years seem to be getting narrower and harder with each new model year of bike coming out... I have a 2007 model, and after only an hour sitting on the stock Honda seat I was hating life and would have sworn I was sitting on a 2x4.
This pictorial was my solution to the problem :-)
Step 1: Prepare the Old Seat
First remove the old seat cover. You'll need a pair of pliers and a small screw driver to pick and pull all the staples out.
Using a black sharpie marker and a ruler, draw out where you want to cut away the stiff foam to make way for some slightly softer stuff.
Step 2: Point of No Return!
Cut away the foam that was marked for removal. I used a sharp bread knife, which worked very well. Shhhhh, don't tell my wife! Hehe!
Step 3: Add Foam
Begin adding the new foam. I used high quality carpet underlay material. It will stand up to the abuse without breaking down and is a little softer than the original seat foam that was carved out. My objective was to make the top of the seat wider, 1/2" taller, and softer.
3M spray on adhesive glue was used to glue the new foam on. A standard 4" angle grinder equipped with a zip cut disc was used to carve and shape it.
Step 4: Add More Foam!
The last layer was a thin piece of open cell high density foam glued over the entire seat. It was used to smooth out the lumpy texture of the carpet underlay which otherwise shows through the vinyl seat cover.
Step 5: Sew Up a New Seat Cover
Using better than marine grade vinyl, I sewed up the new seat cover. Upholstery thread and a 'jeans' needle is needed for this job. The vinyl actually sews pretty easy, even on a basic household sewing machine.
The old original Honda seat cover was used as a general template, and I added material to compensate for the increased width and height of the seat.
Step 6: Stretch the New Seat Cover On
The last step is to stretch the new seat cover onto the new softer seat. I used an air stapler and size T50 stainless steel staples. A hand operated staple gun doesn't have the power to put staples into the seat pan, so you may find yourself at the local hardware store buying an air powered upholstery stapler as I did.
The final touch for me was to contact cement a modified rubber honda key fob onto the rear centre of the seat. I simply used an exacto knife to carefully remove the loop. A mask was made from masking tape (the same shape as the emblem) and was applied to the seat so that the contact cement could be applied precisely without being spread out too far making a mess.
Well there you have it, a new softer seat for fat old farts like me to go trail riding with :-)