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Old 09-06-2016, 08:43 PM
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coopernicus coopernicus is offline
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Default KX 250 2T in a KX250f Aluminum Frame

A lot of folks think about installing a 2 stroke motor into a modern 4 stroke aluminum frame and I have been wondering about this for many years. I recently had to chance to buy a 2007 KX250f frame with a mid nineties KX250 2T motor (bored out to 299cc) installed. I was also very lucky in early July to find a 2003 KX144 that is close enough to a 2007 KX250 to make a rough comparison in ergonomic "feel". Ideally, I would have preferred a '13 or newer KX chassis as that is the year when the KX frames were upgraded to more ergonomically narrow and forgiving ride characteristics.

My initial thoughts on the bike without having ridden it, yet, is that it feels more bulky across the pegs, midsection, and in the rear where the right side number plate bulges outward for the 4T exhaust cannister. It is bulkier than my '14 GG 300 and substantially more bulky than the steel framed '03 KX144. The steel framed 2007 KX 250 (2T) is listed as 214 pounds dry (97kg dry, 226 pounds wet with no gas) and the AF framed 2T weighs 238 pounds (108.2kg) with all fluids, 1 gallon of gas, FMF Turbine Core II, and Maxxis Desert IT tires). If someone is looking to drop some weight by doing this conversion, I don't think it will save you much. It is possible that it weighs more than the equivalent steel 2T frame from the same year KX. What is the advantage that I see at this time? It really looks good!! That's about all I can say before having a chance to ride it on some real trails (coming soon). If the ride quality is not there, then I won't bother to try and put a GG motor into it. For now, I will have to be content with just how good this bike looks!




Eric


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Last edited by coopernicus; 09-06-2016 at 09:08 PM. Reason: embedded a picture
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  #2  
Old 09-06-2016, 09:03 PM
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gasgasman gasgasman is offline
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Cool bike. Thanks for sharing.
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  #3  
Old 09-07-2016, 03:39 AM
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Wonder if it will feel less top heavy, not that the gasser particularly does. Lighter is always nice. Top lightness makes it feel lighter than it is
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Old 09-20-2016, 11:26 PM
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I had the chance to ride this bike extensively this past Saturday and have concluded that I would not bother to make the 4T AF conversion to a 2T motor. The bike had a slightly less top heavy feeling than me 2014 300 Racing E but the width from the pegs to the seat made it more cumbersome. The main drawback compared to a standard KX 250 2T and a GG 300 is the lack of steering precision. It feels a little vague in the turns and does not give the best feedback to the rider as to how far you can "push" the traction on the front tire (which, although new, is a CST brand tire...ewww!). Frankly, this did not surprise me too much given past test reports of the 07 KX250F and the less weight of the KX 2T motor. As for the suspension, this bike has a Race Tech components installed and the suspension is good. However, it is not as good as the bone stock Marzocchi/Reiger combo on my GG. What did I like about the bike besides the 299cc KX motor? The feel of the aluminum frame was far better than anticipated. It was not overly stiff and it did not feel harsh at all. It also had an excellent turning radius compared to my GG (big surprise). I must add, if anyone has a KX 250 that they want to keep, making it a 300 made the motor very nice. I've ridden extensively a big bore YZ and the KX big bore motor is much better for trail and race speeds. The big bore was done by Kustom Kraft but can be done by most other places (Powerseal did the YZ conversion). I don't know if I will keep this bike but I will test it some more after I make some mods to get more "bite" in the front end and I will replace the front tire, too. Feel free to ask my any questions if you are interested in an AF conversion!

Eric
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1974-86 Vintage Can Ams, SWMs, Puchs, etc.
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Old 09-21-2016, 02:06 PM
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Quote:
Originally Posted by coopernicus View Post
I had the chance to ride this bike extensively this past Saturday and have concluded that I would not bother to make the 4T AF conversion to a 2T motor. The bike had a slightly less top heavy feeling than me 2014 300 Racing E but the width from the pegs to the seat made it more cumbersome. The main drawback compared to a standard KX 250 2T and a GG 300 is the lack of steering precision. It feels a little vague in the turns and does not give the best feedback to the rider as to how far you can "push" the traction on the front tire (which, although new, is a CST brand tire...ewww!). Frankly, this did not surprise me too much given past test reports of the 07 KX250F and the less weight of the KX 2T motor. As for the suspension, this bike has a Race Tech components installed and the suspension is good. However, it is not as good as the bone stock Marzocchi/Reiger combo on my GG. What did I like about the bike besides the 299cc KX motor? The feel of the aluminum frame was far better than anticipated. It was not overly stiff and it did not feel harsh at all. It also had an excellent turning radius compared to my GG (big surprise). I must add, if anyone has a KX 250 that they want to keep, making it a 300 made the motor very nice. I've ridden extensively a big bore YZ and the KX big bore motor is much better for trail and race speeds. The big bore was done by Kustom Kraft but can be done by most other places (Powerseal did the YZ conversion). I don't know if I will keep this bike but I will test it some more after I make some mods to get more "bite" in the front end and I will replace the front tire, too. Feel free to ask my any questions if you are interested in an AF conversion!

Eric
Great looking conversion Eric! Ditch the front tire and maybe lower the front spring rate and report back ...
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  #6  
Old 09-22-2016, 12:49 AM
swazi_matt swazi_matt is offline
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Bike looks great, but I always thought the conversion to do for extreme riding was to fit a Kdx motor in the 250f frame
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  #7  
Old 09-22-2016, 11:46 PM
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Quote:
Originally Posted by swazi_matt View Post
Bike looks great, but I always thought the conversion to do for extreme riding was to fit a Kdx motor in the 250f frame
Matt,

You could read my mind from that far away? Used KDXs are very inexpensive here and I recently bought two KDX 220s and was looking for a KX250F rolling chassis to make the conversion. So "yes", an AF KDX was originally my goal. While looking for the KXF chassis, I spotted this bike for sale and, since it was already complete, riding it would let me know if I wanted to go through the effort myself. The answer is most likely "no", it's not worth it. I also found a website where someone put a KDX motor in a KX 125 steel frame and he says it works very well (https://haroldbawlzangya.com). I have a 2003 KX125 and sitting on the AF KX and the steel framed KX (one after the other) shows me how much better the feel is of the ergonomics on the steel framed bike. So now you know the whole story!!

On a side note, for all of you folks outside of the US, if you want to see what the used motorcycle market is like here in the city where I live, follow the link below. My family in the UK is always amazed at what we have here and the prices!

http://denver.craigslist.org/i/motorcycles

Eric
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2018 GG 300 GP
2014 GG 300 Racing E
2002 ATK 605 Dual Sport
2003 KX/KDX 220 hybrid
2021 Kawasaki KRX 1000 Trail Edition
1974-86 Vintage Can Ams, SWMs, Puchs, etc.
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  #8  
Old 09-23-2016, 08:14 AM
hadfield4wd hadfield4wd is offline
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The kdx motor in a 125 chassis is a very common hybrid. But for less money you could just buy a gg200. I looked into it and had the kdx motor and was going to put it in a CR250 AF, because that is what I had. Was just going to be more money than I wanted to spendZ
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