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YZ 250 flywheel weight question

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Hey everyone,

I have a 2010 yz250 two-stroke and I would like to get a flywheel weight for it. I ride motocross only, and I want to make my bike a bit smoother and more tractable. I am having trouble deciding whether to go with a Steahly bolt-on weight or the GYTR complete weighted flywheel. I like the idea of the GYTR, but I can't figure out which Steahly weight it would be comperable to. The GYTR weight only adds 8.25oz, but it is all located on the outermost portion of the flywheel, whereas the Steahly weights the entire thing and should therefore have less inertia mass to it. Any help would be greatly appreciated, as I can't decide what to do, and I don't want to spend 100 bucks without knowing what's what. Thanks in advance.

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I have a GYTR that I don't use anymore. $60 shipped. It will smooth out the hit a little, nice for logs and gnarly hills too.

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I used the steahly on my old yz and bought the gytr for my current 06. The drawback of the steahly was it needed a spacer to fit under the ignition cover....really, no big deal at all, but still...

The gytr is an entire flywheel and fits within the space of the oem ignition cover but will not clear under a aftermarket boyesen cover. The gytr weight is the weight Tim Ferry used on his supercross yz 250 if thats any indication of how much inertia it has....in other words, not so much. I like it, and its close to right, but if it weighed 10 oz I would probably be happier. Again, liek you noted the placement of the weight is a big deal. I'm thinking I would like 2 extra oz on the outside edge.

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It does rev slower, but not much. I dont even know how to offer a comparison, really. Even though it revs a touch slower, the tire hooks up better, so acceleration is probably better with the weight. The flywheel let it hook up, but the piston reved much faster. Scary is my best description of the bike.

You may notice it reving slightly slower down low, but once you get to the midrange it hits very hard and feels stronger than when the bike uses a light flywheel.

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Retarding the timing will take quite a bit of the mid range hit out and make the power very smooth through the entire rpm range. It will add a little bottom end however it will take away some over rev.

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How many degree are you retarding it? Have to be careful because any more then about 2 degrees race fuel is probably necessary?

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How many degree are you retarding it? Have to be careful because any more then about 2 degrees race fuel is probably necessary?

Retarding the timing a bit should actually reduce the octane requirements a bit. Advancing the timing usually does require higher octane fuel.

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I think you might have the terms "advance" and "retard" mixed up. Retard means to spark earlier and advance means to spark later. If the spark is retarded the engine will have greater chance of detonating then if the timing is advanced.

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I think you might have the terms "advance" and "retard" mixed up. Retard means to spark earlier and advance means to spark later. If the spark is retarded the engine will have greater chance of detonating then if the timing is advanced.

I'm actually quite sure about what I said. Advancing the timing means to fire the spark plug further away (earlier)in the cycle from top dead center which contributes to a higher / quicker pressure rise in the cylinder which can also increase octane requirements.

On a 2-stroke advancing the timing also has a major effect on the "effective " pipe tuning length. Advancing puts more of the heat inside the combustion chamber less in the pipe which effectively lengthens the tuning length of the pipe lowering the peak RPM power range of the pipe. Advancing the timing also increases pumping losses at high RPM.

Retarding the timing has the opposite effect with more of the heat shifting to the pipe decreasing it's effective tuning length and reducing high RPM pumping losses.

This is a very basic explanation but it's almost 3 AM and I'm typing this from my phone so I apologize if I left something important out or said something wrong. :lol:

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I think you might have the terms "advance" and "retard" mixed up. Retard means to spark earlier and advance means to spark later. If the spark is retarded the engine will have greater chance of detonating then if the timing is advanced.

sorry dude but, respectfully, I think you're wrong.

According to THE YZ timing thread:

PS Someone who actually wants more hit and an explosive mid range could go

to 1 degree advanced and then try 2 degrees advanced and 3 degrees advanced

This should only be tried with at least a 50% race gas mixture.

The 3 degrees advanced position will most likely require 100% race gas.

Be very aware of detonation before long term use in this configuration

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i have tried both the 9oz and 13 oz weights. i find the 9oz to be perfect. the 13 oz was just a bit too much. the 9oz smoothes the bottom end out and helps a ton with traction. i would go with the steahly 9oz weight for mx. it is super easy to pull on and off too.

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