Powerband Hit

[KingJPW]

So I have a few rides under my belt with my Blaster now. After adjusting the pilot air screw, I was able to get nice response in the lower-to-mid throttle range. However, when moving to full throttle, the powerband hit is so explosive. Tires spin and my body flies backward. I have to release throttle to tame the beast.

What can I do to have a smoother transition from mid-throttle to WOT. Maybe retard the timing a bit? Timing is currently un-modified stock.

 

[Awk08]

What can I do to have a smoother transition from mid-throttle to WOT. .

buy a boring 4 stroke I:I

 

[Wifesblaster]

Advance the timing 4 degrees. This should add a little power down low, which will make it a smoother transition. Just use the search key there is a lot of info on this mod.

 

[Blaaster]

So I have a few rides under my belt with my Blaster now. After adjusting the pilot air screw, I was able to get nice response in the lower-to-mid throttle range. However, when moving to full throttle, the powerband hit is so explosive. Tires spin and my body flies backward. I have to release throttle to tame the beast.

What can I do to have a smoother transition from mid-throttle to WOT. Maybe retard the timing a bit? Timing is currently un-modified stock.

You have just experienced the joy of a 2 stroke I:II:I

Tuning is not just adjusting the air screw, that is mainly used to adjust the idle running.

Power can be controlled by not pressing the thumb lever in so fast and hard.

Although advancing the timing may help to tame the beast, and move the power band down some, the power is still going to come on strong if the jetting is correct.

With the power band being so explosive, you may well be straddling the fine line of a too lean mix.

A 2 stroke jetted on the lean edge will over produce at the expense of engine life.

Check that your jetting and needle setting suits your pipe needs, and then do a plug chop to confirm.

Have you leak tested the motor?

 

[KingJPW]

Advance the timing 4 degrees...

Advance the timing? Interesting. I know on my YZ250 the recommendation is to retard the timing to reduce the hit and making a better trail/woods bike. Can I get a consensus on this? Advance or Retard? I know how to make the mod, just not sure which direction to go.

 

[Blaaster]

From tuning guru Eric Gorr.

Ignition Timing

The ignition timing has a minimal affect on the powerband. Retarding the timing has the affect of reducing the hit of the powerband in the midrange and extending the top end overrev. Overrev is a slang term that describes the useable length of the powerband at high rpm.

The scientific reason for the shift of the powerband to extremely high rpm is because the temperature in the pipe increases with the retarded timing. That is because the burn cycle takes about 55 degrees of crankshaft rotation. When the timing is retarded the burn cycle starts later and continues into the pipe. Raising the exhaust gas temperature raises the velocity of the waves to be more synchronous with the piston speed and port timing of the cylinder.

Advancing the timing has the affect of increasing the midrange hit of the powerband, but makes the power flatten-out at high rpm. The reason is that the relatively long spark lead time enables for a greater pressure rise in the cylinder before the piston reaches TDC. This produces more torque in the midrange but the high pressure contributes to pumping losses at extremely high rpm.

Read the whole article.

http://www.apriliaforum.com/forums/...e-learn-something-about-the-two-stroke-tuning!

 

[KingJPW]

You have just experienced the joy of a 2 stroke I:II:I

Well I also have a two-stroke YZ250, which is like 20 more HP and the ‘hit’ is not as dramatic. I want the power. I NEED the power. Maybe I am complaining about how sudden and dramatic the ‘hit’ is. I wonder if I am rich on the needle clip position (mid throttle) and properly jetted for WOT? Could this cause the symptoms described?

 

[blasterdemon7]

You can also try a 14 tooth front sprocket.

 

[Muggzy]

Re: Re: Powerband Hit

...
Although advancing the timing may help to tame the beast, and move the power band down some, the power is still going to come on strong if the jetting is correct.

With the power band being so explosive, you may well be straddling the fine line of a too lean mix.

A 2 stroke jetted on the lean edge will over produce at the expense of engine life.

Check that your jetting and needle setting suits your pipe needs, and then do a plug chop to confirm.

Have you leak tested the motor?

X2. You may even be a little rich on the needle, making the mid to hi transition even more severe.

 

[KingJPW]

You may even be a little rich on the needle, making the mid to hi transition even more severe.

Here is a picture of a new spark plug after one day of riding. Obviously rich. Also I opened up my carb to clean and check jetting. Results are MJ 280, PJ 32.5, Needle Clip 4th position from top. So I plan to raise clip one position (maybe two positions?) to lean mid throttle. Also I was thinking to remove Airbox Lid to lean it out. I have K&N filter. Maybe I should do plug chop with and without the lid?

 

[Larry's Shee]

My suggestion would be to ONLY change one thing at a time.

What oil and ratio you using? What heat range plug? What is air screw set at? Is float level correct?

Seeing that most riding is done about half throttle, set the clip in the middle.

 

[KingJPW]

What oil and ratio you using?
What heat range plug?
What is air screw set at?
Is float level correct?

What oil and ratio you using? 32:1 Yamalube 2R
What heat range plug? B8ES
What is air screw set at? 2 1/4 turns out
Is float level correct? Yes 20mm measured

set the clip in the middle: Yes will move it from 4 to 3(middle).

 

[Longview]

Well I also have a two-stroke YZ250, which is like 20 more HP and the ‘hit’ is not as dramatic. I want the power. I NEED the power. Maybe I am complaining about how sudden and dramatic the ‘hit’ is. I wonder if I am rich on the needle clip position (mid throttle) and properly jetted for WOT? Could this cause the symptoms described?

If your blaster hits harder than your YZ you have a problem. I can't keep my buddy's CR250 on 2 wheels. Powerband is scary on that thing, Blasters don't even have Power Valves.

 

[Blaaster]

What oil and ratio you using? 32:1 Yamalube 2R
What heat range plug? B8ES
What is air screw set at? 2 1/4 turns out
Is float level correct? Yes 20mm measured

set the clip in the middle: Yes will move it from 4 to 3(middle).

You are approaching the borderline with the pilot jet and air screw setting.

Move the needle clip to the centre slot, re adjust the idle and do a 1/4 throttle plug chop, to confirm the idle/needle settings.