11 vs 13oz flywheel weight, pros and cons?

[Canadian Dave]

11 vs 13oz flywheel weight, what are the pros and cons of each? I've picked up a 99 YZ 250 and intend on using it for some light MX and open trail riding, I have a KDX for everything else. I'm in the market for a flywheel weight and would like to hear from others who have used them. I'm looking for nice tractable power and will likely have the cylinder and head done for more low to mid range. I'm looking to make this a fairly relaxing bike with a more woods oriented power delivery vs MX. Any reason to avoid the 13oz weight in favor of the 11? :think Any one have experience with both?

David

 

[troy2]

Dave,
I have a 2000 Kx250 and purchased a 13oz weight. Never could get the bike to respond the way I wanted until I took it off. If I had it to do over again I would try something around 8oz. or maybe the best thing would be to just ride and get used to the bike and save ~ $100. I also had Eric port it and I installed a V- Force reed valve. Love the power of this bike for off road.

Steve

 

[MN KDXer]

C-Dave,
Give Steahly a call and ask them for advice; they set the kid's and my bike up just fine last spring. The amount of weight for your particular model bike can't really be compared to other model/brand bikes.

I wouldn't send the cylinder away just yet; Regardless of FWW amount, your YZ is going to scuff the KDX in a big way everywhere in the powerband. Get ready to grin! :)

 

[dog]

I have tried flywheel weights on several of my 2 stroke Yamaha Wr250's and have the same comment as previously mentioned that I didn't like the power delivery. If you are going to try one I would go with the lightest available.

I have quite a bit of experience tuning yamaha's for off road use. The biggest improvement I have made is the FMF Gnarly pipe (at least on the older YZ's). This makes the power much more user friendly , in my experience, without making it sluggish. I ride trails, ISDE's, hare scrambles, and a lot of mud/tree roots. If it is slippery, the bike has the power with the Gnarly pipe to pull a higher gear and lug through the nastiness. If traction is good, you can still open it up an rip. With a flywheel weight, the bike seemed sluggish, and I couldn't loft the front end as easily when I needed to. I have also heard that a spacer on the reed block improves bottom end and a smooths the power delivery without making it slow revving.

Despite what the magazines will tell you, in my experince the flywheel weight is not a good way to correct the power band for your riding style. If you think you need one, even the 8 oz will make a big difference.

 

[MARK IT]

I have found that the metal clutch plates work best on my KX but I also
had Eric Gorr work the cyliender. You sould find out what the GNCC guy's
use on there Yamaha's and this may help you. My bike is a total woods
bike now and I race MX every once and a while.

 

[olddirtbaginmt]

Dave:

I have the 99 with the 11oz, my younger friend runs the 8 or 9oz (forget which it is) and his wife runs with the 13oz. I've ridden all, the lighter weight works well if you like a more snap but still keep it from stalls in the tight woods. I could live with the heavier one, but prefer the middle one(maybe thats just because it's my bike). We all have the wide ratio gear set from the WR400 series. We run three different spark arrestors, FMF, Pro Circuit and I have the Acerbis. I originally had the FMF but sold it to my friend in order to purchase the Acerbis thinking it would be quieter. I don't think it is any better and do think the FMF just works better with the bike. As far as a pipe, we have found the stock one hard to beat! You mentioned having it ported, but I personally have found the bike to work well, I run stock gearing and have not found the need to gear down(have run a 13 tooth primary, but it feels smoother with the 14)just for reference I have raced the Porcupine in S. Alberta a few times and there is nothing there that makes me want lower gearing.