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Big bore kit for 05 YZ250F

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I know that there are a lot of threads on big bore kits for the yz250f. But you never get a straight answer. I need something cheap and that will last. I was thinking the forward motion 262 kit, the athena 290 kit, lukes racing 263 or 273 kit or a thumper racing kit. Which should I get?

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The athena kits are nice because you get a new cylinder with the kit, so you can sell your old one to offset the cost or keep it around for spares.

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lukes is the least expensive, foward motion- has great customer service and stands behind there products. thumper racing is another quaility outfit, and athena if you search for posts gets mixed reviews, some say there cylinder had chips in them when they were received, and you have to get in touch with an overseas company. i would personally keep my money in the good old usa and go with lukes, forward motion, or thumper racing. most of the 262 kits are pretty much the same 2mm overbore on the cylinder then replated with a weisco piston. the bigger thumper racing kits (i think the 280 kit) have pressed in sleeve. i have the foward motion kit and have had no problems at all, but i did just install if about 2 months ago and haven't done a ton of riding.

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Yes it does have the iron sleeve (the larger kits 280?), but i don't know about any long term problems.

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The athena kits are nice because you get a new cylinder with the kit, so you can sell your old one to offset the cost or keep it around for spares.

True. I really like the kits from Thumper Racing. All the one's I've ridden have been very nice, later down the road when I change my top-end I'll opt for either the TR 290 kit, or the RPM's 315 Stroker kit, depending on if I'm getting more serious in desert racing or not.

http://www.thumperracingusa.com

http://www.rpmsbigbore.com

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lukes also stands behind their cylinders, he actually called me on a friday night at 8 to make sure I got them. He also took back the one I gouged really bad from siezing the piston cause I forgot to put oil back in the bike and didnt charge me a core charge (dont ask, it was hangover induced :banghead: ). I have almost 2 years on the one on my bike.

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Does anyone have a link to Lukes page? I can't seem to find it

Thanks

Dan

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How much power does the lukes racing 263 get you and the 270. I need some low end because I ride woods but I also want something that revs just as much as stock.

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the 262 gives good power all the way thru the rpms. No clue on the others. You may want to consider a powernow and gearing if all your looking for is low end umph.

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Another Forward Motion and 262cc kit fan here. I've had it installed for almost a year now and it's lasted very well with 1/2 season of hard A senior class Enduro racing. It still runs very crisply and all running gear (valves, etc.) are still in spec. I check everything regularly.

My racing buddy has the 3mm over kit (280?) and the characteristics of the engine are different. It doesn't rev like mine but has more low end. Like YZ250F Rider says above, the 262 kit seems to add more power everywhere and keeps the stock characteristics of the powerband.

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the 262 and the 280 kit (i think i remember reading this) make the same power. the 262 uses a high compression piston, while the 280 kit uses stock compression. you will get more torque from the 280 kit, but the 262 will rev faster (the 2mm wiesco piston in my forward motion kit is lighter than stock).

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Keep in mind that if you intend on racing an ama sanctioned event, the 262 is the only one allowed. The 280 is too big in diameter. AMA only allows for 2mm overbore under repairs.

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On my old '01 I had the thumper racing 280 kit(really a 270). It was great. I race enduro's and it added a ton of low end. It never caused any problems. I definitly did loose some top with that bigbore kit but the trade off for lowend was worth it. If you want to know how much top did i loose? Hard to quantify but you could notice it like the bike didn't wind up as quickly and it just wanted to be shifted earlier. You could hold it open but it worked so much better shifting sooner. It was awesome.

BFS

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Keep in mind that if you intend on racing an ama sanctioned event, the 262 is the only one allowed. The 280 is too big in diameter. AMA only allows for 2mm overbore under repairs.

i think that has been changed. the rules indicate that the 125/lites class is from 100 to 125cc 2-strokes and 126 to 250cc 4-strokes and the 250 class is from 126cc 2-strokes and 251 to 450cc 4-strokes. i had somebody protest me just recently for riding my 262 yzf in the 250 class. some kids mom got pissed because a 35yr old guy kicked her sons ass in both motos.

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This is the words in FTR's rule book. You may want to check yours.

Classification will be made according to

manufacturer's piston displacement marked by

the manufacturer on the engine cylinder.

Displacement may be increased to the maximum

allowable for that class. Cylinders may be overbored

to .080 inches regardless of displacement

and still remain in the original class. See AMA

rule book -"Protests and Offenses."

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