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yz250 Tom Morgan yz295 experience.

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I am the happy owner of a 2016 yz250. I love the bike, the stock motor was great but I wanted something a that was a little bit faster. I gave millennium technologies a call and they told me for my needs I would want the 295 kit ported for mid to top end, milled for pump gas.

I got it together 3 weeks later. No fitment or quality problems. Got my lectron carb tuned up for it, and I was in for a nasty surprise. The motor signs off after half throttle.

I road the bike for 4 months, I only put 15 hours on it. The kit was a disappointment. It made no top end power at all. My brother has a 2017 250sx and his bike pulled on mine like I was on a ttr 125.

I called millennium and they told me that my jetting was off, and I was running too nice of fuel. Didn't know 100 octane hurts motors. And lectrons don't have jets.

The bike ran great, it had a lot of bottom to mid power and was very smooth. It just wasn't what I was looking for. They did not advertise it at all for what it is. I bought another cylinder and it is on its way to Harris Performance right now. I'm not a woods rider, the 295 is perfect for slow technical riding, but it isn't perfect for me.

I'll be posting a review of the HP ported and milled mod 250 engine. I plan on making it a top end screamer cause that's what I've been missing over the past few months.

IMG_9571.JPG

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It had coffee colored spark plugs after running, it was tuned really well, the motor just can't feed the big piston the fuel it needs to rev out, so it runs flat up top.

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Sounds like you need to put the pwk back on there and start leaning it out gradually until you reach spot on jetting. The other issue you would obviously have is trying to use high octane fuel in an engine that is designed to use pump gas.

 

 

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Keep it a 250 port ,match cases, head ,race fuel then you'll have a serious screaming 250😀 big bores take the racey feel away that I like and sounds you do as well

Edited by Motox367
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Tried adjusting timing?  Might need more advance for the larger bore.  Depends on squish band area too though.  Try advancing/retarding, see what you get.

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I'd pull that 295 cylinder off and send it to Eric Gorr for a port job.....I have 2 cylinders from him...one was for motocross and the other Supercross. They aren't the standard porting for off road or the "mo Betta".  The mx porting revs to the moon while the Supercross hits hard and sign off earlier. Neither display the characteristics you describe.

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I already sold the cylinder to someone that was looking for that type of power, I traded for a 2012 stock cylinder

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On 1/5/2018 at 3:41 PM, orangyktmthing said:

The bigger the bore, the leaner you go. The engine actually will pull more fuel, compared to a standard bore engine.

Meaning: all other engine factors besides bore size being equal, a bigger bore mod will use smaller jets (just to keep the same AFR) Like you said, a bigger engine sucks harder though the same size carb and jet (making it richer).

That being said, well, what IS the right main jet?

It's the main jet that pulls the hardest at high rpm at full throttle.

Edited by Marc Salvisberg
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I was running a EG 295 with mid/top porting, it didn't sign off early.

Now I run a ported Athena 293, it doesn't sign of early.

Obviously you had porting and set up issues.

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I was running a EG 295 with mid/top porting, it didn't sign off early.
Now I run a ported Athena 293, it doesn't sign of early.
Obviously you had porting and set up issues.

That's exactly what I thought because I have tried absolutely everything, but they just told me it was me causing the problems. I think it wasn't ported properly.

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That's exactly what I thought because I have tried absolutely everything, but they just told me it was me causing the problems. I think it wasn't ported properly.

Did you ever get to personally talk to Tom? Sounds like the cylinder could have been ported for low-mid power. He might of been told to port it that way. Hard telling, but I will say this, I had Tom do work for me years back and never once had an issue. He knows engines every bit as well as Eric Gorr.

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Did you ever get to personally talk to Tom? Sounds like the cylinder could have been ported for low-mid power. He might of been told to port it that way. Hard telling, but I will say this, I had Tom do work for me years back and never once had an issue. He knows engines every bit as well as Eric Gorr.

I did, I was told I had the wrong jetting in it. Then I told him what jetting I had, and he was confused what could be wrong with it after that. He asked if wanted to send it back, but instead I sold the cylinder to someone that was seeking that type of power.

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I had Millennium do a 295 kit on my '99 RM250 last fall, needed to split the cases and grind down a small boss below the exhaust port to clear the piston otherwise it's a bolt on deal.  I also had to go one size down on the main and the pilot, runs great now!  Had it ported for more power throughout the entire range and they delivered!  Sort of wished that I had told them to try and mimic a KTM300XC powerband (not sure if they could), but still, it's faster than ever and I'm completely satisfied. 

These kits go a long ways towards breathing new life into old bikes.  I totally recommend trying a 295 kit if you own a 250 2t that you really like or can't afford 8 or 9 grand for a new one.

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Typical 2 stroke big bore that is why I ride a 250 .

The Power is there if all is set up perfect, the transfer ports lack the ability to flow enough on the top end.

Even if all is set up perfect they always feel a bit less free reving.

They are a great woods set ups though and make good power if you shift early enough.

 

 

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