YZ300 kit gearing suggestions

[Hillzy]

I have a 13 YZ250 that I'm going to install an Athena 300 kit on when I need a piston change. The bike has 8 hours on it currently. I have the kit already and the head and cylinder are in the hands of Eric Gorr for porting and squish correction.

 

My question is on gearing for motocross. I currently run a GYTR 8.04 oz flywheel with 14/51 on a stock motor. What is the best gearing with the 300 kit?

 

I was thinking 14/48 or 14/49........thoughts anyone?

[chrispick]

Tall, it will pull hard so I dont waste it on wheelspin

[numroe]

I find a well tuned (broad ported) 295 will pull 14/48 no problems.  Much less gear shifting than a stock bore motor. But if you previously liked 14/51 with the stocker and/or if you are a heavy guy, then you might prefer 14/49.  2 teeth less on the rear is substantial.  Less chain guide wear is a nice bonus. Mine last for ages.

With tuning to jetting and spark timing, you should be able to move the 295 power around to your liking. I find a broad powered 295 with Fatty pipe still pulls a lot stronger+broader down low than a well tuned 249cc YZ motor with a gnarly pipe.  You rarely need to wait, wish or clutch with the 295. It pulls down low and before you know it you're moving pretty quick again. You can tune it to have a low RPM hit or not. What ever power floats your boat.  At present I'm using a 249cc top end with the base shaved for low RPM grunt and std comp, and no matter what jetting or pipe I try it's always more work than the 295.  On just about any dirt type too.

Beware that EG might not give you a normal (1.3 to 1.5mm) squish setup. Not sure if or why he does it his old way.  With correct squish+comp I think they respond better (more sane) to changes to jetting or spark timing. A fun engine to own and use. Sound awesome too.  I'm missing mine. In case you didn't notice.

[Hillzy]

Thanks numroe, just what I wanted to hear. I'm 195 and will be going with 14/49. I was going to wait until my bike needed a piston to install the kit, but after reading your response I am rethinking that thought. I am trying to make this a do it all bike so I don't get 450 fever again.

[Ron W]

Do the 300 kit and then ride a 450 back to back. You'll be done with the 450's.

[numroe]

17 hours ago, Hillzy said:

I am trying to make this a do it all bike so I don't get 450 fever again.

Good plan.

[scootersbikes]

Not to hijack anything but I just traded my 450 straight up for a yz250 and I think when its time it will be a 295. Which is the best one to go with?

I didn't realize how much I missed the 2T smell and hit. 

[Coop's OffRoad Performance]

On July 31, 2017 at 11:00 AM, chrispick said:

Tall, it will pull hard so I dont waste it on wheelspin

RMATV has a Wide ratio kit for the transmission?

[Hillzy]

Not to hijack anything but I just traded my 450 straight up for a yz250 and I think when its time it will be a 295. Which is the best one to go with?

I didn't realize how much I missed the 2T smell and hit. 

Scooter, I went with the Athena kit so I could have the stock cylinder, head, and power valve assembly available for a spare or to go back to 250 if I wanted.  The Athena quality was top notch.  I did have Eric Gorr port the Athena cylinder and set the squish.  I went big bore on another 250 smoker and I was displeased with the grinding that was done on the power valve for clearance.  I have about 3 hours of run time on the bike so far and I am very pleased.  I ended up settling on 14/48 gearing, which seems to be about perfect.