KX250F BB Kit?

mxbigd17
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mxbigd17
Edited Date/Time 6/9/2017 8:47pm
Ok, anyone and everyone please chime in if you've had experience with building up a 250F please. I'm torn on what to do so I need some feedback about your experiences...good and bad.

I talked to Tom Morgan about modding my 2015 KX250F. You guys know.....port/polish some kind of head work, hot cams, HC piston.......OR everything mentioned above except running a 270cc kit.

I ride a lot of practice days and race occasionally, usually the age classes +25/30/40. I'm a decent rider, went from 250t to 450f bikes but this is my first 250f bike and I really like it because it handles a lot better than a 450 and I don't get wore out in 6 laps of riding it. I'm an average size guy 5'11, 185 lbs so the 250f isn't horrible by any means. But on a full gate in the age classes, guys usually have 450's which makes getting a start tough but not impossible. A little more power wouldn't hurt and I'm not interested in going back to a 2t.

What have you guys done to your bikes, was it worth it or not? Who was the engine builder, was the bike reliable or did it require way to much maintenance above and beyond normal maintenance. Was the HP gains really noticeable and worth the price tag? Just needing some feedback....
And by the way....why is Porting/Polishing so damn expensive!
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Paw Paw 271
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Paw Paw 271 5/11/2017 7:40am
5/11/2017 7:40am
I put a RPM 272cc ice cube kit in my 250f and loved every minute of it.

Paw Paw
Millennium Technologies 5/11/2017 7:55am
5/11/2017 7:55am
Obliviously, I am biased...but I love my YZ270F. Light like a 250, but makes 43hp. Low compression, runs pump gas, super reliable. Love it.

Tom is a good engine builder too.......lol.
mxbigd17
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mxbigd17 5/11/2017 8:24am
5/11/2017 8:24am
I put this in the wrong thread a few weeks ago and have already sent it out to Tom. I love hearing feed back that's about this kind of stuff. Bench racing about bike builds to me is fun. I'm really excited to ride my bike after TMR works his magic on it. I'm old and slow....but that doesn't mean the bike has to be. lol
Millennium Technologies 5/11/2017 8:37am
5/11/2017 8:37am
mxbigd17 wrote:
I put this in the wrong thread a few weeks ago and have already sent it out to Tom. I love hearing feed back that's about...
I put this in the wrong thread a few weeks ago and have already sent it out to Tom. I love hearing feed back that's about this kind of stuff. Bench racing about bike builds to me is fun. I'm really excited to ride my bike after TMR works his magic on it. I'm old and slow....but that doesn't mean the bike has to be. lol
Awesome. You will be happy. When I did the 270 kit on my bike, it was like a whole new bike....

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rmstrg
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rmstrg 5/11/2017 10:31am
5/11/2017 10:31am
I had a RMZ that I put a 270 in, stage 1 hot cams, no port or polish, yosh exhaust, and vortex ECU. I put over 100 hours on it with no problems. It had more torque than my Ktm 350, pulled very hard. I really loved the bike and actually was thinking about getting rid of my 350 and getting a 250 and doing that again.
Bruneval
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Bruneval 5/11/2017 1:10pm
5/11/2017 1:10pm
I turned a 2009 KXF into a 290cc with an Athena kit. The bike rips and will keep up with pretty much anything, and has a noticeable amount of extra torque over a standard 250F. It took a while to get the fueling right, but that was more to do with setting it up for the UK and the different fuel than anything else. Being a carb bike, I just bit the bullet and put it on a dyno to get set-up properly but a modern EFI shouldn't be a problem in the same way. Sure Tom Morgan will send yours back good to go though.

The KXF engine responds very well to the big-bore in my opinion, and it has been very reliable. I have bought other bikes since but kept the KXF as I like having it around. It's not your usual spec, so perhaps isn't a fair reflection - it is an ex PC race bike (see the plugs in the engine case and the mounts on the back of the right radiator for the oil cooler) with a ported PC head, titanium valve train and PC cam/exhaust. It has no problem revving out.



mxbigd17
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mxbigd17 5/11/2017 4:54pm
5/11/2017 4:54pm
So it seems you guys really liked the bike after the kits were installed and other adjustments were made to take advantage of the new big bore. I was going to buy a new bike but thought what the hell, lets try something different. I don't think you can go wrong with a TMR build, ohhh I can't wait to ride it.


My buddy has the exact same bike as me, 2015 KX250F. It's going to be pretty cool to ride the bikes back to back since his is all stock and mine will be built up.

I just don't want to ride a 450 anymore, I spend to much energy trying not to over do it and hurt myself annnd then I over do it and hurt myself. Lol
mxbigd17
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mxbigd17 5/12/2017 7:28am
5/12/2017 7:28am
Bruneval wrote:
I turned a 2009 KXF into a 290cc with an Athena kit. The bike rips and will keep up with pretty much anything, and has a...
I turned a 2009 KXF into a 290cc with an Athena kit. The bike rips and will keep up with pretty much anything, and has a noticeable amount of extra torque over a standard 250F. It took a while to get the fueling right, but that was more to do with setting it up for the UK and the different fuel than anything else. Being a carb bike, I just bit the bullet and put it on a dyno to get set-up properly but a modern EFI shouldn't be a problem in the same way. Sure Tom Morgan will send yours back good to go though.

The KXF engine responds very well to the big-bore in my opinion, and it has been very reliable. I have bought other bikes since but kept the KXF as I like having it around. It's not your usual spec, so perhaps isn't a fair reflection - it is an ex PC race bike (see the plugs in the engine case and the mounts on the back of the right radiator for the oil cooler) with a ported PC head, titanium valve train and PC cam/exhaust. It has no problem revving out.



It sounds like your bike rips! Has anyone had their transmission polished or had the R.E.M. treatment done? If so, what are the real world benefits of having the transmission serviced like that? My bike is not the best shifting compared to the other bikes I've owned. Any advice would be much appreciated.
mxbigd17
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mxbigd17 6/7/2017 7:33pm
6/7/2017 7:33pm
Well, TMR racing did my engine work and just got it back today. Looking forward to putting it back in the frame and testing this puppy out.
Millennium Technologies 6/8/2017 6:50am
6/8/2017 6:50am
mxbigd17 wrote:
Well, TMR racing did my engine work and just got it back today. Looking forward to putting it back in the frame and testing this puppy...
Well, TMR racing did my engine work and just got it back today. Looking forward to putting it back in the frame and testing this puppy out.
You are going to love it!
Moto520
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Moto520 6/8/2017 8:56am
6/8/2017 8:56am
I have a 270 kit, FMF exhaust, higher RPM rev limiter, and a few other mods done by Tom Zont Racing. I run race gas and the bike has been bulletproof as well as fast. Much different experience than a 450 and excellent for tighter tracks. I love it.
ktm-5
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ktm-5 6/9/2017 12:20am
6/9/2017 12:20am
If the kx still seems lacking it doesn't take much to get a ktm 250sxf to 50hp and still be super reliable
Charper732
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Charper732 6/9/2017 8:47pm
6/9/2017 8:47pm Edited Date/Time 6/9/2017 8:50pm
I can tell you to STAY AWAY from Athena BB kits. I know most guys just get the kit and slap it on without measuring anything. When I got my kit I measured everything. I CC'd my head which was only decked .005" and CC'd the piston at the top of the stroke. They claim the comp rating is 12.8:1. I measured everything 3 times and each time it came out to 10.6:1!!

I called them out on it and asked for what their deck height, squish, CC measurments and they wouldn't tell me anything. Their response "oh, we don't give out those kind of specifications". Complete horse shit. What really blew my mind, when I explained to their tech my findings he responded with "Oh, most guys don't measure the kit when they install it"...talk about shady business practices

I ended up having to get JE to make me a custom piston to get the compression up to where I wanted it.

So I ended up with the price of the Athena kit, plus another $300 piston to make up for their shitty engineering. I will never buy another Athena product as long as I live.

Edit: Speaking of which, I sold that bike, but I still have a higher comp piston kit that ill let go for a good price if anyone with a 290 kit is interested.

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