YZ250 big bore kit
- Thread starter rwild
- Start date
A 265 would be ok but I would only do it if my cylinder got scored somehow. It would probably slightly increase bottom with a slight reduction in max rpms due to more moving mass.
I rode one and it didnt seem any faster. It was an 05. It did seem to lug up a technical hill better.
I rode one and it didnt seem any faster. It was an 05. It did seem to lug up a technical hill better.
2 strokes for life
Member
- Jan 3, 2007
- 1,860
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I have heard lots about the YZ330 kit. http://www.madmanengineering.com/bigborekits.htm
MikeT
~SPONSOR~
- Jan 17, 2001
- 4,112
- 11
A small overbore that only ups your cc's a little won't be noticeable. I rode back to back my old 125 with another identical bike same year and everything bored out to a 133 and it made no difference at all to me. For the cost I think putting money into tires or some Boyesen reeds would have been a better bang for the buck. JMO
A 330 on the stock jug would be problems, imo. If that kit is a different cylinder made specifically for a 330, that would be different. Supposedly, there is a custom 330 cylinder out there. There would be powervalve issues either way.
I would love to hear from someone who has either setup as that would be killer for me. You would definitely lose some max rpm with a 330.
I would love to hear from someone who has either setup as that would be killer for me. You would definitely lose some max rpm with a 330.
I have a 2001 YZ 250 I bought used from a wanna be racer kid. Its only slighly bored (my doing) but is worlds better and lighter than my friends highly modified KX 500.
I sent my cylinder and head to Eric Gorr and asked him to turn up the torque (Mo Better i think is what he called it). He took material off the base of the cylinder, bored it to a 265, ported it (including casting epoxy), changed the head chamber, set the squish band height and sent it back to me very quickly. There is an incredible change engines HP and torque. Torque is much higher at slower speeds, yet it still punches up and wants to wheelie out of 3nd. Its aggressive but very controllable on tight trails and throttle response is very quick. I just got back from northern Baja where I spent 3 days on a CRF450X and my bike is better at the rocky tight stuff. Much better. The CRF has the torque but it is slow to come up. Bummer. I bought my bike for 1800 bucks and now have under 3 grand it altogether into it counting Erics work. I have 8 grand saved up for a new bike and now I am going to put that back in the bank and ride mine until the frame breaks, if ever. Dont neglect proper porting and tuning ion your current machines when considering these pricey big bore kits. Mine is bored up but I can buy stock wisco 68.5mm pistons.
FMF Gnarly
Turbine Core 2
Boysen two stage reeds
Magura Clutch
G2 throttle cam
9 OZ flywheel weight
Stock sprocket tooth count and a 19 inch tire.
Dave
I sent my cylinder and head to Eric Gorr and asked him to turn up the torque (Mo Better i think is what he called it). He took material off the base of the cylinder, bored it to a 265, ported it (including casting epoxy), changed the head chamber, set the squish band height and sent it back to me very quickly. There is an incredible change engines HP and torque. Torque is much higher at slower speeds, yet it still punches up and wants to wheelie out of 3nd. Its aggressive but very controllable on tight trails and throttle response is very quick. I just got back from northern Baja where I spent 3 days on a CRF450X and my bike is better at the rocky tight stuff. Much better. The CRF has the torque but it is slow to come up. Bummer. I bought my bike for 1800 bucks and now have under 3 grand it altogether into it counting Erics work. I have 8 grand saved up for a new bike and now I am going to put that back in the bank and ride mine until the frame breaks, if ever. Dont neglect proper porting and tuning ion your current machines when considering these pricey big bore kits. Mine is bored up but I can buy stock wisco 68.5mm pistons.
FMF Gnarly
Turbine Core 2
Boysen two stage reeds
Magura Clutch
G2 throttle cam
9 OZ flywheel weight
Stock sprocket tooth count and a 19 inch tire.
Dave
Solid State
Member
- Mar 9, 2001
- 493
- 0
Why the juice clutch? The stock one is pretty sweet. Just curious.
2 strokes for life
Member
- Jan 3, 2007
- 1,860
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The 330 is a hole new cyclender made by niki. It has a special power valve machined for the big bore. But i know i cant ride a YZ250 to its full hype, it would add insult to injurie to put on the 330 kit.
Yeah but you cant bore the cylinder without modifying the power valve, so send the cylinder including the powervalve, and head.
Turn around was very quick. He was done and ready to send in a week or so.
"Juice clutch" I only put on a ride ago or so. It is a little easier but probably not worth the money if your biking on a budget. Stock clutch worked well after I shortened the lever a bit but routing was in the way of Moose hand guards. I got it from a friend new but cheap so I did it.
Eric Gores work is worth the money, and after parts and machining and tax etc etc I am still not even to half of the cost of a new 4 stroke that feels less powerfull. Leaves enough money to buy the very best protective gear and all the good stuff for your garage and truck. HA!
Dave
Turn around was very quick. He was done and ready to send in a week or so.
"Juice clutch" I only put on a ride ago or so. It is a little easier but probably not worth the money if your biking on a budget. Stock clutch worked well after I shortened the lever a bit but routing was in the way of Moose hand guards. I got it from a friend new but cheap so I did it.
Eric Gores work is worth the money, and after parts and machining and tax etc etc I am still not even to half of the cost of a new 4 stroke that feels less powerfull. Leaves enough money to buy the very best protective gear and all the good stuff for your garage and truck. HA!
Dave
rockers109
Member
- Oct 13, 2002
- 38
- 0
If the work is done correctly on the cylinder and of course it's installed and tuned correctly you can definetly benefit from overboring the cylinder. Every bike I ever had I always eventually added more power by overboring it and some porting it. I just got a 265 cylinder for my rm 250 from Eric. I rode it for the first time today and boy what a difference, pulls much harder out of turns and pulls longer on straights without the hard hit that the stocker had.
