Ok, let me clear some of this up. A stock Blaster spark plug is indeed an NGK B8ES. You can run the "R" version (BR8ES) with no problems, but it is not needed. (The R is for Resistor. You don't need a resistor plug in a Blaster).
Here's the manual. See for yourself:
http://www.blasterforum.com/general-support-17/downloadable-yamaha-blaster-manual-17325/
That primer kit you're looking at works well for its intended use, but you don't want to use it on a Blaster. Why? Well, that primer squirts a LOT of fuel because most of the time it is designed to feed two or more carbs at the same time. Putting one on a Blaster will only flood the carburetor and engine, and you'll never get it started.
If your Blasty isn't starting properly and all the above has been checked (compression, presence of spark, etc), you've got another problem preventing easy starting. An aftermarket carburetor will NOT make the engine difficult to start. I run a giant 34mm Mikuni and I only need the "choke" when its 60 degrees or cooler outside. Most of the time it starts in one kick with no "choke" whatsoever.
SO, first thing to check are your reeds. Even a slight chip or crack will make starting difficult.
Reeds OK? Check your carb jetting. Let's see a pic of that carb. Most Keihins like between a 42 and a 45 pilot jet on an otherwise stock engine. If the pilot is way too big or too small, good luck getting it going when cold.
