Yamaha YZ ESR 325 (2-T) Review

Derek Harris wrote:

I'll save you the dyno run time. I took a video of it with the customer prior to the run. I told him what a stock...

I'll save you the dyno run time.

I took a video of it with the customer prior to the run. I told him what a stock yz250 makes on our dyno (45-46), then asked him what he expected his ESR 325 to make. His comment was "It rips, must be 55 hp".
Bike has FMF pipe, PC silencer, and vforce and he had run the jetting around the ringer to get it to run right. ESR sent him some suggestions - and he was close, but he had constant bogging issues he couldn't quite resolve.

This first chart is as suggested by ESR as a base - then lots of track testing with both the Powervalve setting and the jetting.




Now is a mod 250cc combo vs this 325



And lastly is a low end woods style mod 250 vs the 325 combo




Sadly the customer made it to hour 30 and the piston shattered into a million pieces. I applaud ESR for his efforts and his vision. I hope the product takes off - with some development it can make some good HP. But I hate the steel liner - this is a huge step backwards in technology and requires a looser fit to prevent seizures - which isn't good for durability. Our customer was so fed up with various bog issues and constant "finicky" ness - he went back to a 250. Once back to the 250 - his comments were the "vibration is much less" and it's quicker to rev (as expected)


The actual power output of the 325 per cc sucks - but is much better than stock - and much better than the most common 300 cc "big bore" sold. I hope the kit can go towards plating rather than a steel liner - and some port work goes a long way.

Derek Harris wrote:

In those posts is a mod 250cc. Its 5-6hp up and flat out a blast to ride, ultra reliable and easy to jet. Our 265 tuned...

In those posts is a mod 250cc.

Its 5-6hp up and flat out a blast to ride, ultra reliable and easy to jet.

Our 265 tuned in vs our 250 mod is a tad better everywhere once the pv opens.


Past 265 cc the cylinder has major issues. Our 250 mod out dynos the most popular 300 kit sold everywhere in the curve. Its been our experience that most people do not have their 250 stock tuned in for best performance.... So when they go to some kits out there they inevitably start tuning that kit to get it best... And are much better than their untuned stocker... But not much better than a well tuned stocker.
With half and hald c12 and pump, a stock port and head yz250 with some added ignition timing and ur favorite pipe can gain huge hp when jetting is right. Few people make use of this resource..
Once your making this power the bike responds extremely well to a 48 rear sprocket to spread it out.

cwtoyota wrote:

Derek, I tend to agree. The same is true for the Athena YZ144 kit vs an un-ported OEM cylinder with good tuning. Yamaha put a LOT...

Derek, I tend to agree. The same is true for the Athena YZ144 kit vs an un-ported OEM cylinder with good tuning.

Yamaha put a LOT of refinement into these bikes over many years and it takes a whole lot of work to do much better in terms of power character. Most of the big bore kits out there have a ton of power in one place, but don't have the broad, linear power like a well tuned OEM cylinder.

Delivery is more important to me than maximum power.

I prefer a tuned up YZ250 over a KTM/Husky 250 because the YZ is so broad and linear. I really feel like the new model KTM engine with the Mikuni carb is a step backward (in stock trim) from what I felt on the older engines in the 2011 / 2012 models.

The exception is the TX300 Husky. That engine goes flat on top, just like the current TC250, but it has so much low/mid torque that you can pull a taller gear and ride it like a true open class machine.

Derek Harris wrote:

Still less power than a new ktm...

SDTony YZ ESR 325 wrote:

[img]https://p.vitalmx.com/photos/forums/2019/04/22/341111/s1200_IMG_20181208_120116538_HDR.jpg[/img] Updated with ESR Decals and Pipe

Updated with ESR Decals and Pipe

Derek Harris wrote:

Still less power than a new ktm...