what is my next mod to be?

Porting and a head mod will make huge gains in power. If you remove your lid for the air box don't forget to jump up the main jet in your carb.

X2 on head mod, worth every penny.

It really comes down to what you want to spend.. Also remember with more power it is a good idea to upgrade the handling.

rob the mods you mention make a difference without porting or head work ,

i've done all the diy mods myself also adding +4 timing advance and using a bolt on uni air filter jetted to suit it rips running premix also

Head mod is the best bang for the buck in my opinion

you could also lighten the flywheel but x3 on porting and head mod

also lightened flywheel and carb boring

removing the airbox lid is said to make a little difference.
i always go for a CFM but the more air the more fuel it can pump in right?
remember to re-jet

benharcombe1985 said:

rob the mods you mention make a difference without porting or head work ,

i've done all the diy mods myself also adding +4 timing advance and using a bolt on uni air filter jetted to suit it rips running premix also

Click to expand...

using just a podfilter is not always the best option. i ran one until i could afford a CFM and was worried every time i had to go through water

if you are looking for top end power look for a right bend. you should have your carb bored or buy a new one that is around 30mm or below after getting a right bend, some people go bigger too. removing the airbox lid doesnt do much besides make it sound better, i did it because why not. i always have heard great things about the head mod. Tors removal is just a reliability mod, no power gains to be had... Reeds are cheap and increase throttle response.

Rob-daisy said:

Thanks. As ive just had the engine rebuilt iwillwait for the head bore. Just looking for bits that can be done whike still runnin the bike. What is the best exhaust. Left or right for more top end that is.

Click to expand...

a right bend for more top end. i run a trinity pipe and love it but a bigger carb is needed to match the pipe.

Power is fun and there exists no such thing as too much IMO, but I'm all for handling here. You'd be mind blown at the difference a good suspension setup will make. You can have it widened and stretched a bit with some good Works double rates and you'll have way more fun with however much power you have.

Of course, more power comes after that. Or before.

My suggestion for power:
Head mod
Porting
3mil stroker - if you go this route, have the porting and head mod done for a 3 mil build

You can do like I was attempting to do with my Banshee and buy another engine that's trashed and build what you want out of it. That way, you don't lose any ride time before the winter season kicks in AND you can have that time to build the engine how you want it AND you can have a backup engine. Drop the money on another carb and jet it to that engine and make life a breeze. That does take money, but you gotta pay to play.

My son and I tinkered with his stock Blaster, tried some typical 2 stroke tuning tricks to get power, (compression, carb, air, exhaust, porting, timing) but quickly found combustion shape was the bottleneck to power. I think this was done on purpose by Yamaha to limit the stress and power on what was designed to be a "beginner" quad. Get a $60-$80 modified head as the very first mod. Set the squish gap between piston and head at 1mm and then do a plug chop to get the jetting right. This mod alone will result in about a 30-50% power increase or about 23-27hp with everything else completely stock.

Without a modified head:
a pipe will gain you 2-5hp (magazine tests from the day)
a larger carb will gain nothing but trouble (tried it)
intake porting will gain 0-3hp at more revs (gesstimate based on experience)
Exhaust port raised increased rpm, decreased low rpm torque and gained 1-4hp at revs
3mm stroke is a 5% increase so will gain a 5% power increase, 17hp x 5% = 0.85hp
milling 0.5mm off the head (2.5mm squish) yielded more torque on bottom end
milling 1mm off the head (2mm squish) yielded detonation (tried it)
+4 timing = more torque on bottom end, perhaps a bit on top (tried it) 1-2hp?
Boost bottle - can you feel anything? I can't feel anything...
Reed spacer - I think I feel something...
Reeds - yup, I'm pretty sure I feel something...

Put all these mods together and you might get to 27hp.
Or much less and be buzzy and need to be rev'd just to get moving.
A head mod, pipe, and 1mm raised exhaust port will see you over 30hp still with great low end torque.
Shim the airbox cover open or drill a couple extra air holes may help too.
You won't need the +4 timing mod. The improved combustion shape speeds burn.

Some pictures below:

Stock Blaster (front right), modified (rear) and a modern motocross head (front left)


Even with modified heads there are different shapes possible for different powerbands:


Red represents what I FILL IN with epoxy on the intake side after opening the windows up slightly.
The exhaust port I would raise 1mm and make "D" shaped, with the flat to the top (still curved slightly)


There is more, but basically start with a modified cylinder head.

Steve