Power band characteristics

I am try to get some low end grunt out of my 2010 YZ250, the engine seems very revvy compared to my 02 250. What have others found that works?

 

Here are the combinations I have tried.

 

stock everything

added 9 oz FWW

added 51 tooth sprocket

Machined off 0.015" the head

added V force 3 reeds

added procircuit shorty

added procircuit pipe

I had Derrick Harris port my jug and added his power valve spring I could not be any more happy with it. Pulls like a tractor with a nice and smooth from top to bottom.

any more info on the powrvalve spring?

It added more low end and smoothed out the hit. It was a easy install. Derrick Harris has them.

any more info on the powrvalve spring?

Power valve spring? Ive never heard of that. What is it? How much does it Cost? What are the pros and cons?

Is this Harrperf?

I don't know the price as I had my whole engine done at the same time. I installed the spring a week later to test, I don't see any cons unless you like having a huge hit to cause wheel spin. 

 

Yes it is Harrperf.

Hey man,

 

On my 250, i added a gnarly, vforce3 reeds, and a pc shorty. It's an 01 and the bottom end power is crazy. Though it has lost a lot of over-rev. You basically have to pick bottom or top end power with these things

Have derrick set up your engine and you can have top and bottom.. I let a buddy ride my bike and he said" this thing is cheating, like riding a 450"

stiffer spring maybe used to slow down the opening point.

Seriously, try a FMF Gnarly. It will give you GOBS of low end grunt. I tested mine out last weekend and was blown away. But like slagenthor said, you will lose top end. Not a problem if you're doing woods riding.

Porting + head mods are the best bang for the buck if you want to gain horsepower and move the powerband around.

 

For just moving the powerband, play with your gearing.

I'll weigh in, we all have different ways of achieving more bottom end this is just what worked on mine.  my 05 YZ is a goat set up for woods and rocky hill climbing,  I'm not a pin it kinda guy either more trials like..... read as I have to go to work tomorrow!  Any way heres what I did and the end result I had so much bottom that I had to go 3 teeth smaller on the rear. 

  1. Set timing according to spec, I've worked on 4 newer YZs all had advanced timing and funny the factory ping went away when set right.... not sure whats up with that
  2. V force reeds -  didn't really make a big difference
  3. Yamaha GYTR heavy flywheel - good addition but not a miracle worker, yes I would do it again
  4. stock pipe, tried several of the bottom end pipes and liked stock best
  5. R+B designs did the squish and bored carb, blade, and modded the slide - damn best money I ever spent on the engine,  I went one richer than his pilot recommendation to get the bottom a bit more blubbery so it wouldnt just rip the tire loose in the woods

you will lose some top end and over run but it depends on what youre after, I run mine on pump gas and 32/1 Honda HR2 oil, if I'm running hard no spooge but honestly have found that cleaning spooge is easier than doing a top end... and dyno results have proven over and over that higher oil concentrations give more power if jetted right.

the squish is really key if you look around the net theres info regarding it.  I build a lot of street 2 strokes and its one of the best mods you can do, more power less prone to ping, and pump gas. 

Seriously, try a FMF Gnarly. It will give you GOBS of low end grunt. I tested mine out last weekend and was blown away. But like slagenthor said, you will lose top end. Not a problem if you're doing woods riding.

I will say it once again. Gnarly.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now