Playin in the sand

[blastinfools]

So a buddy and I went to play in the sand for the first time, last weekend, and I was a little disappointed in my blasters performance. I have a new wiseco piston stock bore, boyesen super stock carbon reads, FMF gold fatty with turbine core 2 pipe, K&N filter uncovered, just put a 280 jet in on the 3rd notch, and I'm runnin ITP sandstar front and rears on ITP aluminum wheels with a 1½" spacer on the rear, the rears are 20X11-10R and fronts are 22X8-10R, banshee front shocks with a 400ex rear on the way. I know it was sand, and I may have expected too much of these tires, but I just didn't seem to have as much torque to start, 5th and 6th gear seemed to be super boggy. Any suggestions as to what I could do to make next time more exciting, I wanna be able to get the front end up and play it out with throttle and blast off the top of dunes, keep in mind that trails are the majority of my riding but when I make the trip to the dunes (3hr minimum ) I want the best experience possible, so maybe some things that would make the best of both worlds.

Y'all never let me down, so bring it on

 

[yamaha28]

what gearing are you running? Might want to drop one in the front when running those 20inch tires

 

[piezzi]

Port work and a bigger carb are needed if you're serious about sand.

 

[blastinfools]

That is kinda what I was thinkin, i'm runnin stock gearing, and I was hoping to not have to port until I'm due for another top end. Are there other power options that i've missed, what do y'all think about those reed cage spacers?

 

[Surfrjag]

reed spacers arent going to do much or anything really.. try a gearing change and advance the timing 3*. if you want some more power your going to need a port job. what exhaust are you running?

 

[blastinfools]

what gearing should I shoot for, 11/40 12/40 12/42...

 

[blastinfools]

FMF w/turbine 2

 

[blastinfools]

how do I go about advancing the timing? turning the stator? how do you judge 3*

 

[Surfrjag]

There is a walkthrough on the timing mod on here somewhere. I think its 3mm on the stator. Stock gearing is pretty low so you may just want more power overall, the porting would be your next step along with a larger carb..

 

[Larry's Shee]

Sand sucks the powwa out of everything X( Try dropping front 1 tooth. How many paddles? Check that all wheels roll smoothly. I:I

 

[Blaner]

you dont seem to have missed much performance wise APART from porting and a redesigned head. which coincidently is where all the power is. Anything other than porting is not real "POWWAAA" my advice? for the immediate/temp solution, lower your gearing, maybe pop in a 300 main..sand tends to be hard on motors and anything slightly lean will be enhanced and damage can occur. Perhaps richen your needle one clip by moving the clip DOWN one position.

Long term, Get that thing ported, add some Aux boost ports, get the head reshaped and pop on a 28-35mm PWK carb. Bang...your sorted.

 

[best]

Sand is where my son and I usually play with our Blasters.
Mine is overpowered to begin with the KTM engine, but his stock was a bit underpowered.
We modified the head and dropped the cylinder (left out the base gasket, sealer only) and it is much more torquey at the moment.
Hillclimbs in 3rd gear and pull 6th over the sand without bog on the stock 15/40 gearing.
His will now start away without throttle at idle and easily starts away in 3rd.
We tried just dropping the cylinder without the head mod and had problems with detonation.
Dropping the cylinder tends to move the powerband down into the mid range, raising the cylinder moves the powerband up into the upper rpm range.
Opening up the chamber in the head encourages turbulance and discourages detonation at all rpm.

 

[blasty 95]

Idk if the ktm blaster has 15 tooth up front..but i would never never run a 15 on a blaster...

 

[Blaner]

interesting Best, ive never heard of anyone dropping the cyl. I have mine raised. Do you have the port timing specs there? One thing to consider is that your transfers and exhaust will never be completely open when lowering. Reducing port time, and the step the piston creates surely damages scavenging efficiency

 

[best]

Idk if the ktm blaster has 15 tooth up front..but i would never never run a 15 on a blaster...

Sorry, just checked. He is running a 14 on his Blaster.
I am running 12/44 on my KTM Blaster because of the oversize tires and motor's internal gear ratio, quite tall.
Cannot be compared to the Yamaha motor sprocketing.
The 12 is kind of small too. Chews into the swingarm bushing. Oh well, it is a wear item...
I do not recommend the over sized tires by-the-way. Eat a lot of power and handle terrible.

 

[83jeepcj5]

getta +3 stroker lol solves lots of probms

 

[best]

interesting Best, ive never heard of anyone dropping the cyl. I have mine raised. Do you have the port timing specs there? One thing to consider is that your transfers and exhaust will never be completely open when lowering. Reducing port time, and the step the piston creates surely damages scavenging efficiency

This is a learning project for my son (and me too I guess, at least to re-affirm theory).
We put a DT200 head on an engine and made use of its high ports and RPM band earlier.
Present engine is to show what can be done with lowering the ports and torque band.
The DT200 cylinder had to be ridden on powerband, whereas this motor is fat and strong
in the lower revs. It excels on hillclimbs because as the rpm drop, it just gets stronger.
It is not a finished project. There is no "powerband" like we are used to on a 2 stroke.
It probably only makes 25ish hp, but makes it quick on the low end and holds it to max.
The goal now is to keep that low end torque, and yet still have 35+hp on top end.
In the end we will be shimming the basegasket back up, but with substantial head
and port work.

Consider that your transfers and exhaust are only ever completely open for a brief flash
in cycle time anyway, so it becomes immaterial. The ports on these engines are made
for a 58-59mm stroke and have that shrouding problem to begin with on a stock engine.
It is like this engine was MADE for a stroker. My son has a 3mm stroker but we are
still exploring just how we are going to set it up with port timing. This is part of the
experiment. If you want to play on the sand hill, this did work well.

 

[DirtDiggler]

Hey Blastin , I'm in Tacoma Too !!! Where abouts are you? Where did you go ride? I ride out in Sand Lake , Florence , Winchester and Coos Bay , hit me up , we can find that extra power in your blasty waiting to get out .

 

[Blaner]

Interesting stuff best, im glad to see you know what you are doing and its always good to experiment if you can afford to

I see the merits of your attemp in looking to get the bottom end pull. However i (politely) disagree on your point that not fully opening the ports is immaterial. If the ports opened fully, yes it would be for a brief millisecond, but put it into perspective, a minor change in port area makes a hug difference, think about how many times that piston opens and closes those ports per minute, second even. Think about it this way, what would be the point of porting and adjusting port sizes minimally to achieve amazing power results if what you said holds, porting then would simply not be effective.

Any little change in port height OR barrel height makes HUGE changes to the charactger of the motor, you have seen this yourself by lowering the barrel.

It is my opinion that Yamaha designed this engine to be underpowered.

This is an extract i typed out once in a email to our Aussie cousin Blaaster:

"Yamaha designed the Blaster as an entry level sport quad, they didn’t want it biting the heads of little kids! So they tamed it by skimming 1mm off the bottom of the barrel to retard the port timings! Also, by adding the spacer, it allows for the piston to fully uncover the exhaust and transfer ports at BDC, which it normally doesn’t do!

Also G.Bell says the ideal squish thickness of the head is between 1mm - 1.4mm depending on whether its a 175 or 250cc Stock blasters is 2.53mm and 1.8mm (different on different sides of the head to direct combustion away from spark hence detuning further, although some say it is to cater for expansion on the exhaust side.
Ideally you want a center spark motor, all things explode in a hemispherical nature, ever seen a cone shaped explosion on the A-Team? The blasters use a Cone shaped combustion design which then obviously is not conducive to good explosions! Editing the head is a major improvement that simply must be done."

You can see this port timing paradigm by measuring port specs, I will post them as soon as I can format them.

 

[best]

Blaner, it may sound ironic, but I completely agree with you.
As we work on these engines it becomes very obvious that they are well designed, but detuned.
I can see the missing mm you are talking about, the piston still covers the bottom port by 1mm stock.
We narrowed the quench down to 1.8mm, centered the spark and gave it room for toroidal swirl.
Some of these factors are more important than the lowered ports for the power increase.
The lowered ports (port timing) just affected where the power occurred.

Here is why I feel what happens at the bottom of the port is of less importance in our instance:
Most of the "activity" that takes place in both the intake and exhaust ports takes place at the very top.
Whether it is the initial pressure release or the final capture, it happens at the top.
The top of the port sets the timing, and it directs the flow, and is exposed for the entire duration.
The bottom of the port affects none of this, and is exposed for only a few degrees of rotation.
The top of the port is critical, the sides determine area and are important, the bottom least.
So while you are right, it is not immaterial (I know, I said it!), the bottom of the port is not hugely significant.

So what we did in this set-up was sacrifice bottom edge of the port for duration (port timing).
In this instance the increased low rpm torque offset the port area loss and piston edge flow
interruption at a few degrees of rotation at BDC. The port area loss was not critical
because we were looking for results at lower rpm anyway. Make sense?

The whole trick will be to find the best height for each of the ports to make broad power.
The DT200 shows us that 32hp can be had by just raising the intake and exhaust ports.
This works by increasing RPM, increased power strokes/minute. However the mid-range is lost
(and the powervalve does not fully fill it in).

You mentioned "always good to experiment if you can afford to".
We have gathered some spare parts but we are not rich. The largest cost is time.
2 strokes are kind this way. You don't need a lot of expensive parts for them.
And these Blasters are kinder yet, tons of hidden HP just waiting to be let out.

My son and I are working methodically at finding the right compression ratio, port height,
and chamber shape to make strong power throughout the range.
We are looking to beat that KTM!