KX250F big bore reports?

[John407]

my '04 KX250F is ready for a rebuild (or at least a check up, no problems at all). There is one guy up here that has a 290 kit on his, he says it is the best bike he's ever had. I've raced (or tried to keep up to) him a couple of times on my YZ450. It does not pull as hard as the 450 but it's not that far off, and best of all it's still nimble.

Anyone have one, or rather anyone have a big bore kit and have run it for awhile? Hows the clutch hold up? Hows the cooling? Starting? Compression braking? Cost?

I'm tring to justify doing the big bore kit instead of rebuilding with stock parts. Thanks for your opinions

[KX250FER]

my '04 KX250F is ready for a rebuild (or at least a check up, no problems at all). There is one guy up here that has a 290 kit on his, he says it is the best bike he's ever had. I've raced (or tried to keep up to) him a couple of times on my YZ450. It does not pull as hard as the 450 but it's not that far off, and best of all it's still nimble.

Anyone have one, or rather anyone have a big bore kit and have run it for awhile? Hows the clutch hold up? Hows the cooling? Starting? Compression braking? Cost?

I'm tring to justify doing the big bore kit instead of rebuilding with stock parts. Thanks for your opinions

Ill let you know on my 290 ATHENA this week. They are $599 and you get a compelte bolt on kit. Well worth it so far!!! just have to ge time to test the freakin thing!

[hart]

With all the problems the 04 has I'd stay away from a big bore. Mains are weak, cases are weak clutch basket gear is weak, 3d and 4th gear are weak, etc. eric gorr says it's the most failure prone 250f of the lot. I wanted the 290 also but I'm too scared of problems.

[WIfarmer]

My buddy has the ice cube 276 (something like that) kit in his 04 and has had no problems. We ride once a week, race once a week, and he rides up north (U.P. of michigan trails) a few times a summer.

[John407]

With all the problems the 04 has I'd stay away from a big bore. Mains are weak, cases are weak clutch basket gear is weak, 3d and 4th gear are weak, etc. eric gorr says it's the most failure prone 250f of the lot. I wanted the 290 also but I'm too scared of problems.

Thanks for the responses. My '04 has been great but I do scare easily. When Eric Gore said this did he mean that compared to the '05 and '06 KXF it was weak? Or was he comparing it to the blue and red 250F's ?

What changes did Kawi make to the '05s? I did hear about the gears, but when i checked the part numbers they were the same. I thought that an updated part had a new number.

I used to race a Stroker 365 KLX (started out as a 250KLX) and the KXF, even my '04, is better starting point. At least from what I can tell.

Thanks again for the opinions.

[faster48]

I have the Athena 290 kit on one of my '04's. It's been on since last spring with no trouble what so ever. It has gobs of low and mid but doesn't rev as quick or far as the stock displacement bike. I went down one tooth on the rear sprocket but it still needs a little more. I'm sure that the top end could be better with new cams, but I'm pretty comfortable short shifting it. I will say that I can pull great starts on that bike in the vet classes even against 450's.

Hope this helps...

[John407]

Actually it does help. I have only seen one big bore KX250F (most of the time all I can see id the rear fender disappearing). He seems to love his, he is fast and he rides more than I do. So the bike has some hours on it. Thanks

[Rick_Peterson]

Re: KX250F big bore reports?

Posted By Hart

With all the problems the 04 has I'd stay away from a big bore. Mains are weak, cases are weak clutch basket gear is weak, 3d and 4th gear are weak, etc. eric gorr says it's the most failure prone 250f of the lot. I wanted the 290 also but I'm too scared of problems.

Hi Hart,

I'm Rick Peterson of MaxPower-RPMs. We build the KX276F ICE CUBE that WiFarmer's buddy has. For most riders a Big Bore kit will increase the longevity of the motor parts you listed. Because less shifting and less clutch fanning is needed, the clutch and tranny normally take less abuse with the Big bore. And, because you can shift earlier, often run a gear taller, and scream the motor less, the main bearings in theory should last longer, and the valves absolutely do last longer. The ICE CUBES, and, I believe, the Athena kits also hold more coolant than stock.

I'm not saying that a 16 year old maniac that slams into the rev-limiter on every shift (because he knows Dad's buying) can't break a 276 just as fast as he'd break a KX250F, but for the average sensible thumpertalk rider, I would expect the MaxRPMs KX276F or the Athena KX290F to EXTEND, rather than REDUCE engine life.

When the rules permit it, there never has been a better way to increase overall power than a Big Bore kit. Both the 276 and 290 and our KX315F are much more durable than a KX250F with larger cams, stiffer springs and crazy compression. The KX315F uses a taller version of the 81mm ICE CUBE. It holds 3 times as much coolant as the OEM cylinder. The crank is stroked 8mm and we also use a longer rod that is the much stronger "I-Beam" type.

Factory Kawasaki Offroad Racer, Cole Calkins has told me several times that his KX315F is the best offroad bike he's ever ridden for East Coast events.

Factory Yamaha Offroad's Randy Hawkins said that his YZ315F works better than a 250F, 450F or 250 2-stroke for offroad events. Obviously, both of these guys put these bikes to harder use than most riders.

I just wanted to set the record straight. You CAN break a properly engineered Big Bore, but if you care for it properly, it will give you a better service life than you've come to expect from less-thouroughly engineered kits.

If you want to learn more about our ICE CUBE cylinders, please visit this link:

http://maxpower-engines.com/big-bore-kits/kx-rm315f.htm

Feel free to post on TT or e-mail me at rpmsbigbore@aol.com with any tech questions you have. I answer e-mails about 4 hours a night and I love doing it!

Hope this helps,

Rick Peterson

To avoid any confusion, here's the latest on the MaxPower-RPMs merger:

I'm the founder of Rick Peterson Motor Sports AKA (RPMs) or rpmsbigbore.com

We are best known for our cylinder re-plating and 2-stroke kits like the YZ-139, YZ167, KX105, YZ112, etc.

Because the OEM 4-stroke cylinders can only be reliably bored 2mm over,

I developed the ICE CUBE Billet Aluminum, nikasil plated, viton o-ringed cylinder 2 years ago. We have kits for the 250F's and 450F's, but not minibikes.

I was recently bought out by MaxPower-Engines.com from Madison, WI.

Now we're called MaxRPMs

I'm now the Product Designer and Tech Consultant. (So I finally have time to play on TT!)

I design, dyno and test the kits here in Ontario, CA. We also machine the CUBES and stroke the cranks here and ship them to MaxRPMs to assemble.

All of the cylinder plating, motorwork and parts are in Madison, Wisconsin.

[kantoniak]

Well Rick, thank you for that explanation. I have never considered the big bore kits due to infered reliability problems. I know this is you business, (both to explain and sell) but it is nice to see an experienced explanation. Who knows, maybe I will consider going back to a 250F with a big bore some day!!

[Pontificus Maximus]

As long as Rick is coming on here I want to plug his Ice Cube 276 kit. I've been running it about a month now and could not be happier. I thought about the Athena kit but was a little worried about their pistons longevity because I ride once or twice a week year round. The Ice Cube is top notch stuff. I am told the cylinder plating is thicker than what is used in cast cylinders and can be honed to one of several incremental oversizes rather than replating it. The head gasket uses o-rings. The outer one looks reusable and the inner round one appears to be a stock Yamaha part number.

Also, I was concerned that my motor wouldn't rev as high with it but that doesn't seem to be the case. Before I put the Ice Cube on I was barely clearing a third gear jump (at Perris) if I let it rev out. After, I could clear it easily. I let a guy that has a '05 CRF450 ride it and he thought it pulled about the same as his 450 from the mid and up.

Do I get some free stickers now?

[goodtogo]

Nice to here some one tell it like it is ....I get my 06 kxf 250 next week ....I have the site bookmarked....

[LBiggie]

Rick-

Do you recommend any carb, jetting, sprocket or rear tire changes to accompany your 276 kit? I have an '05 KX 250F with the full Pro Circuit exhaust and had to re-jet it substantially (per Pro Ciruit specs) to get it to run correctly, but now it goes great. I also have the JD race ignition on it.

I'm also thinking about this option instead of buying a new bike would like to know what other changes are needed to bolster performance. Thanks.

-Lance

[Nystrom]

Would the 276 kit fit on a 06? And how is this kit compared to a Athena 290kit? Is it 2 pistons included?

[hart]

He says the kxf is maybe the worst reliable bike ever! Not trying to start a battle but 2 pro builders I've delt with say the 04 kxf is a good play bike but run it competition mx and it will fail in many ways. I suppose your average enduro riders and casual mx guys like me may not have problems. eric gorr says the crank/rod is too weak to handle the big bore. He's probably talking long term. I'm sure 80% of the people will run just fine but I don't want to be in the 20%. check it out yourself..

http://www.ericgorr.com/services/fourstroke.html

[KevinMcGrath]

The cranks, among other things, have been strengthened and improved substantially since '04.

[stormwire]

He says the kxf is maybe the worst reliable bike ever! Not trying to start a battle but 2 pro builders I've delt with say the 04 kxf is a good play bike but run it competition mx and it will fail in many ways. I suppose your average enduro riders and casual mx guys like me may not have problems. eric gorr says the crank/rod is too weak to handle the big bore. He's probably talking long term. I'm sure 80% of the people will run just fine but I don't want to be in the 20%. check it out yourself..

http://www.ericgorr.com/services/fourstroke.html

That link is a very usefull read. The reason I say that is because I am about to get a 2004 KX250f for cheap b/c I did some work for a guy. I know these bikes have their issues in 2004, but I am going to be using it specifically for enduro and hare-scrambles. I think it will hold up just fine, but I might be interested in some of the "upgrades that eric gorr" mentioned !

Thanks for the information and just keep your fingers crossed for me ! LOL !

[hart]

If you know the weak points you can keep your eyes on them. Since I've had mine down to the last bolt because of the weak basket gear problem, I'm pretty familiar with it and like to work on it too. I plan to ride mine for years but I'm ready to have it apart when it needs it. and that will be more than most 250f's

[Rick_Peterson]

Re: KX250F big bore reports?

Rick-

Do you recommend any carb, jetting, sprocket or rear tire changes to accompany your 276 kit? I have an '05 KX 250F with the full Pro Circuit exhaust and had to re-jet it substantially (per Pro Ciruit specs) to get it to run correctly, but now it goes great. I also have the JD race ignition on it.

I'm also thinking about this option instead of buying a new bike would like to know what other changes are needed to bolster performance. Thanks.

-Lance

Hi LBiggie,

Here is our suggested jetting spec:

Suggested Setup at Sea Level, 75 degrees (change as needed to match conditions): 100 Octane, 168-175 main (stock is 178), 42 pilot (stock is 40), needle #4 position., 2 turns out, FMF pipe best peak and great for overall power, but some riders say it hits too hard on flat turns, Bill's or Leo-Vince pipe has good roll on. I only tested the pre-production PC pipe. In early 04 it was all bottom end. I'm not sure how it works in late 05?

I've played with #110 rear tires, and with #100 tires on a 250-2-stroke rim, but the stock rear tire and stock gearing works great with the KX276F.

I have not tested the JD ignition, but in general, I don't like the idea of extending the rev-limit.

I've only been posting on TT for a week, but I've got quite a bit of related information on these posts. Please check it out and then hit me with any unanswered questions. The Wife will be home after a week in Texas and I have some cleaning to do!

https://www.thumpertalk.com/forum/showthread.php?t=305583

https://www.thumpertalk.com/forum/showthread.php?t=306009

https://www.thumpertalk.com/forum/showthread.php?t=306009

https://www.thumpertalk.com/forum/showthread.php?t=306009

https://www.thumpertalk.com/forum/showthread.php?t=306009

Rick Peterson

MaxPower-RPMs

PS-Here are excerpts from 2 e-mails I got this weekend from 04-05 KX/RMZ 276 and 315 ICE CUBE owners. Maybe they can convince you to keep your trusty old sled and upgrade it!

RMZ315F

11-20-05

Rick,

I just wanted to let you know how I feel about the bike now that I have had a chance to race it.

The bike exceeds my expectations. It flat out rips. It is like riding a mini 450 in terms of the way the motor works.

I got holeshots in both motos yesterday. The bike is a pleasure to ride. I think it is the perfect motorcycle.

Thanks again for designing the perfect motor.

Rick You ROCK!!!!

Steve Landsberg

Note-Steve traded in his RMZ276 ICE CUBE and stepped up to the RMZ315 last week so that he'd have the will-power to avoid buying a new bike.

The good news is that when he gets weak, anyway, in about 5 months, the 276 or the 315 kit will bolt right onto his 06 model.......~

Here's a recent RMZ276 owner:

RMZ276F

11-18-05

Hello,

I have just bought a 2005 Suzuki RM-Z250 that already had the Ice Cube on it.

First off, let me tell you that I LOVE the power that bike puts out!

Thanks for the help and a GREAT product! Almost hate to tell anyone else about it but they all want to know what I'm smiling about when I get off the track...hehehe!

Many blessing and a Happy Thanksgiving!

Vinny Vanturini

[Rick_Peterson]

Re: KX250F big bore reports?

Would the 276 kit fit on a 06? And how is this kit compared to a Athena 290kit? Is it 2 pistons included?

Hi Nystrom,

Yes, the KX/RMZ276F ICE CUBE fits the 04 to 06 model. So does the KX/RMZ315F ICE CUBE with Stroker Crank. For the record,

The YZ276F ICE CUBE fits the 01 to 06 models and the YZ315F ICE CUBE does, too. The 01 and 02 crank has a different flywheel, but if you run the crank and flywheel from an 01-02 YZ302F or YZ315F in the 03-06 model, it will run perfectly.

The 03 to 06 YZ315F cranks are 100% interchangeable.

The 04-06 CRF276 ICE CUBE and and CRF302 ICE CUBE with Stroker crank kits are identical.

Whew! Got that off my plate!

We no longer sell the ICE CUBE with 2 pistons for $1,200.00. It now comes with 1 piston and gasket kit for $999.99

Some of the pictures on maxpower-engines.com are out of date, but the descriptions below each kit list what comes with it.

Donn Maeda at TWMX just took a bunch of killer pictures of our new CUBES which are polished before anodizing, and then LAZER etched. They look KILLER and will be on the website soon. You can see a YFZ488 CUBE in several colors at http://maxpower-engines.com/atv-icecubekits.htm

The billet aluminum/nikasil plated ICE CUBE cylinder was designed from scratch to be very stout. I could easily go to an 83mm piston, but I like the performance of the 81mm better overall.

The Athena 290 feels like it has more bottom, but less top end than the KX276F. The 83mm KX290F vibrates a little too much for my personal taste, so I elected to go with the 81mm 276cc piston.

As Jodi Weisel at MXA has said more than once, "I want it to run like a Big, Small bike, not a Small Big Bike."

From my testing, going past 276cc on just the bore of the KX/RMZ and YZ250F makes them feel like Slow Open Bikes. The 276cc, though, revs freely like a 250F rider is accustomed to.

Once the bore reaches a certain size, about 81mm on the KXF and YZ250F, the stroke must be increased to get the bike to breath properly and rev freely.

Ah! I'm starting to get long winded again! I better wind down and start my Sunday Morning cleaning.... (at 2:46 PM, that is

I've posted a lot of Big Bore information on the threads I listed in my e-mail above. Please look them over and hit me with any unanswered questions!

Rick Peterson

MaxPower-RPMs

[tat2guy]

So does this affect the handling of the bike??? I currently have an 06 CRF450 butt would like something I could do a H/S on one weekend and go to an MX the next weekend. I am a mid pack Vet B rider in both.