This is a neat Motocross action magazine video feature done on a beautiful yz250 built by Michael Shaw for Jared Leshar. We have been playing around on the engine combo some to chase the delivery needed for Pro Supercross, and a lot has been learned in a short time!
We have a GET CDI installed, and we have been playing around on maps to get the best combo of snap and over rev.
One thing we have learned is very little time is spent at peak HP! These guys are always looking to get the bike to lug down as low as possible, come out aggressively then continue to pull well past peak hp. Little tiny changes in ignition curve and powerjet function translate to big feel changes on track. If we pull 1 deg of timing Jared can notice.
On the cylinder head, luckily Luke at Phathead was able to pitch in and send a billet head that allowed us to rapidly test different head inserts for best feel and overall power character. Interestingly - we ended on a very low compression combo, but thanks to the rapid insert change ability we have been running a higher compression insert for the arenacross rounds Jared Has hit
Porting wise, I've made a few small tweaks from our std package with the goal to maximize power as the powervalve is opening - but at the same time minimize the hit. We found in our first combo that the powervalve would open it it would hit like a mule making it hard to control on jump faces. Jared said "it liked to be lugged" in early feedback, and after some questioning - what he meant was - if I don't lug it - it snaps on too hard. So we altered the relationship between main exhaust port and auxillary exhaust ports to make the powervalve opening transition smoother. If we chase this another season - we will chase wider and wider power vs more power. Of course more power would be great too. We have a request in with FMF on something a little special too - if we can get lucky on that.
The piston is a wiseco we run - it's not a yz250 piston, but it allows us to do some things in porting the OEM doesn't allow. It's a single ring piston, and we really like the overal durability and performance it allows us.
The carb is stock size, with a STIC metering block. We feel the improved throttle response and over rev are hard to match any other way with the carb. The jetting is relatively consistent week to week due to the stadiums being indoor - but Michael uses and iphone app that displays Relative Air density and as needed, we fine tune for the local conditions.
A flywheel weight was added early in the SX series - and that really helped. I think all YZ250 owners should run one - it just helps put the power down. Even in the quick snap demands of SX it has been better.
Starts have been an issue - with Jared struggling to keep the front end down! Not what we expected but it's a big issue! We have a prototype product in the works to hopefully assist with this for the last couple rounds, I strongly feel if we can get him in position off a start to qualify - his riding has been good and he can put it in the main, which would be the first two stroke in the big boy class since 2006!
Be sure to follow Jared's social media - and reach out to him if you'd like to support him. He is truly stringing this along out of a sprinter - with the help of just good people and companies.
We have a GET CDI installed, and we have been playing around on maps to get the best combo of snap and over rev.
One thing we have learned is very little time is spent at peak HP! These guys are always looking to get the bike to lug down as low as possible, come out aggressively then continue to pull well past peak hp. Little tiny changes in ignition curve and powerjet function translate to big feel changes on track. If we pull 1 deg of timing Jared can notice.
On the cylinder head, luckily Luke at Phathead was able to pitch in and send a billet head that allowed us to rapidly test different head inserts for best feel and overall power character. Interestingly - we ended on a very low compression combo, but thanks to the rapid insert change ability we have been running a higher compression insert for the arenacross rounds Jared Has hit
Porting wise, I've made a few small tweaks from our std package with the goal to maximize power as the powervalve is opening - but at the same time minimize the hit. We found in our first combo that the powervalve would open it it would hit like a mule making it hard to control on jump faces. Jared said "it liked to be lugged" in early feedback, and after some questioning - what he meant was - if I don't lug it - it snaps on too hard. So we altered the relationship between main exhaust port and auxillary exhaust ports to make the powervalve opening transition smoother. If we chase this another season - we will chase wider and wider power vs more power. Of course more power would be great too. We have a request in with FMF on something a little special too - if we can get lucky on that.
The piston is a wiseco we run - it's not a yz250 piston, but it allows us to do some things in porting the OEM doesn't allow. It's a single ring piston, and we really like the overal durability and performance it allows us.
The carb is stock size, with a STIC metering block. We feel the improved throttle response and over rev are hard to match any other way with the carb. The jetting is relatively consistent week to week due to the stadiums being indoor - but Michael uses and iphone app that displays Relative Air density and as needed, we fine tune for the local conditions.
A flywheel weight was added early in the SX series - and that really helped. I think all YZ250 owners should run one - it just helps put the power down. Even in the quick snap demands of SX it has been better.
Starts have been an issue - with Jared struggling to keep the front end down! Not what we expected but it's a big issue! We have a prototype product in the works to hopefully assist with this for the last couple rounds, I strongly feel if we can get him in position off a start to qualify - his riding has been good and he can put it in the main, which would be the first two stroke in the big boy class since 2006!
Be sure to follow Jared's social media - and reach out to him if you'd like to support him. He is truly stringing this along out of a sprinter - with the help of just good people and companies.
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