#1) $60 5hp+ Modified cylinder head
Set that head on the left rear to 1mm piston clearance and jet the carb, you go from 17hp to 22, easily.
#2) $10 3hp+ Grind 1mm off the top of the exhaust port. This is a stock one, upside-down.
Flatten the top edge 1mm higher, widen and square its top edge while you are at it.
This will pick up your rpm. Done right and jetted, you should be up to 25hp.
#3) $150 3hp Aftermarket pipe.
Depending on which pipe and how well you did the first 2 mods, you could be at 27-29hp by now.
This pipe won't fit your Blaster, I cheated, but you get the picture.
#4) $0-$40 2hp Air lid mod. Pretty much gotta do the previous mods before you need this.
No exact picture cuz I went crazy with mine, but shim the lid up, drill holes in it, or replace it with a waterskin.
You can make 30-35hp with this set-up on the stock carb and without altering the timing.
Do these mods right and you will be running with the big boys, begging for better shocks and brakes.
The biggest key on a Blaster is that modified head, very first thing to do. Buy one.
Steve