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klx250 engineswap


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Hey guys ,

has anyone ever tried an engine swap on the klx 250 s ?

I was thinking of trying to shoe horn a kfx 450 r 4wheeler engine with @ 60 hp into my klx 250 s frame.

Ya I know that the stock engine can be improved but i already have a 300 top end and a jet kit and the engine is still a turd. cams , porting,and pumper carb cost almost as much as a new mill with a net of @ 30-35 hp

The real issue is that I also ride a yz 250 that has loads of power ,and the klx in similar situations will get me in over my head with its lack of response and wheel poping thump.

I would not even consider a loud exuast as the dualsporting that we get into can somtimes endus up on questionable property .stealth is a must .Not saying we go around gates or any obvious barier but when you end up in someones back yard off a trail you dont want to be poping 105 db.

we get into more exsporer riding than anything else.

so the goal would be a 450 carburated quite mill with @ 50to55 hp in the klx 250s frame.would want to retain e-start and battery charging .

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This comes up frequently, and I contend that most people don't know how much work and how many variables are involved to put an engine of a complete other series into a frame of a complete other series. Yes, it's possible to do with enough mechanical experience, plenty of fabrication knowledge, plenty of decently high tech tools and welding capability...at least to do it right. Where would the donor bike for the 450 engine come from? Wouldn't a KLX450 engine be a better choice?

The KLX250/300 series is a good, solid, basic bike and probably not worthy of such an effort, time, and money. These types of swaps were more popular back in the day when someone wanted a 4-stroke dirt bike in a really good chassis, but only the competition 2-strokes had good frames and suspension. That's not really the case anymore.

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So I get it an engine swap is not easy.

The main concerns are the rear of the engines similar.As for the front mount goes thats not a problem I have a complete machine shop with mill ,lathe , chopsaws etc. As for mechanical ability and fabrication ability goes 30 years of wrenching on bikes and karts has taught me to ask questions of why it shouldent be done and then make an educated decision on the cost benifit ratio. On the flip side as a gun smith with 7 world titles under my belt when breaking new ground i listen then do what I want.So somebody please talk me out of this before the wife finds out what I want to do.

It may not be worth the effort but can it be done??

The donner will come from e-bay found a 2008 kfx e-start r 4wheeler motor for 1400 has the starter in the right area also has the kawasaki stator and proper pigtail.the big question is the rear mount swing arm arangment. if the donner engine is narrower thats not a problem as I can spin up some proper spacers. if its larger thats an issue.I would have to machine the swig arm. thats not desirable or machine back the cases .Also not desirable but resonable.

The advantage to such a proposition would be a serious trail/ street bike that doesent have the ktm pricetag.

Maybee I should sell the klx and find a used ktm . may /or maynot cost a little more but will get me there quicker.

the obvious solution is for Kawaski to make the klx 450 street legal.

I would buy one tomorrow.But I dont think it would compare to the kx series engines.

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Frankly I would love to see a project like this and have you post an ongoing thread on the progress. I love stuff like that. But...I still think that it would be an act of love and not of logic.

On the KX ATV engine, is that engine basically identical to the KX motocross engine? I understand your issue on the availability of the ATV motor, but I disagree with your assessment of the comparison of the KX series engine to the KLX450 engine...at least if the KX engine is the same racing item in the motocross bike. The KLX motor will be better suited to a street legal application than a KX motocross engine. The KLX valvetrain and some other issues are more durable than the KX series, yet the KLX isn't some kind of wimp motor by any means. Many would say the KLX450 may be the ideal candidate for a serious dual sport. If you'd be unhappy with the power of a KLX450, you need to get a KTM530 street legal enduro model or such. Are you sure you're not thinking of the KLX400 dual sport model in your comment?

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From what I understand the atv engine is the same as the motocross engine with slightly different cam profiles producing more down low with less over rev.the nice thing is the starter and stator arangment.

As far as a klx 450 goes I havent seen any engines out there yet. Also consider that the dualsporting that I get into is either close to the house couple miles or the bike is trailerd into the ride zone. so I realy dont do much hwy or heavytrafic areas.My truck isnt very far away is the point,so reliability is an issue just not the most important in this endevore. My coments on the klx are based on my klx . my thinking is that the 450 is going to have maybe a 20% increse from where I am now. based on the platforms being similar ,cam profiles,valvetrain ,durability factor ,exuast restrictions etc.any one ever dyno a klx 450??

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No, I think you're off on the KLX450 horsepower. The KLX250 produces about 18hp...20% increase would only yield about 4hp. The KLX450 should have close to twice the hp of the KLX250, and I don't think I'm stretching that. I still think you have the wrong bike in your thoughts here. The KLX450 is based on the KX engine with some more durability built into the the valvetrain and a heavier flywheel. Regardless, the ATV KX450 engine would probably be just fine, as I'll bet it has a heavy flywheel too for ATV use. I would like to see a project like this and would enjoy seeing it progress. Let's get started.­čĹŹ

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is the reasoning to keep the frame/vin b/c of the street legalness?

I would think it would be easier to just get a klx400 or drz400 plated for street use rather than putting the biger engine in a sucky frame. Just my .02. I love my bike and all, but the frame is my least favorite part, all the way from the weak steering head to the non removable rear subframe.

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I would agree that the stock 250 motor is a dude. But rememder I already have a 300 topend on board with the proper jeting . the engine works as it should just doesent have any power compared to my yz.just dont want to spend any more on this engine.based on the dyno reports out there the kx plants are puting down @ 50 stock with 60 possible .Or am i misinformed??

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I would agree that the stock 250 motor is a dude. But rememder I already have a 300 topend on board with the proper jeting . the engine works as it should just doesent have any power compared to my yz.just dont want to spend any more on this engine.based on the dyno reports out there the kx plants are puting down @ 50 stock with 60 possible .Or am i misinformed??

There's a dyno report on this site that shows a KXF450 putting out 46.7hp with a slip-on and proper jetting. The KLX450 would only be slightly behind that. I'm not trying to slam your idea at all, but the KLX250 frame/chassis isn't the candidate for a near 50hp engine...guaranteed. I would honestly still enjoy seeing a project like this, but I think you'll be way ahead and a lot happier with an engine and chassis meant for each other.

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I would find a KTM 2 stroke for street use if you want performance with the ability to ride it down a road or two. A lot of KTM's come w/ a street ready title. "ktm cost' shouldn't be an issue nowadays, value of bikes are at a near bottom right now. I made my klx street legal in alabama, I would assume plating a dirtbike in georgia is fairly easy as well. It takes patience, but its doable. Took me about 6 months going back and forth with the DMV at our state capital.YOu'll never get your klx, even w/ a 450 motor, to act like your YZ. I had a KX 250 and sold it b/c I didn't like that sort of power. I prefer a tamer bike like the KLX.Some do, some don't. Sounds like the KLX is not your bogey mav.

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Sat on a KTM 530 street legal job. man thats a tall bike. 38 inch high seat .

I thought my nose was going to start bleeding.

The sales guy said it would settle down and they would put a low seat on

the unit and put black plastics on . they said they could lower the suspension about an inch also.

Man they wanted to sale that bike. But realy they where the nicest dealers I have ever been to. Kind of like a private sale from A guy who doesent need to sale the bike.

So you guys have talked me out of the project . probable will keep the bike for the boys to go with me.Now to talk the wife into the $ 8000+ KTM. wonder if she would even notice. I could paint it green i guess .

As far as the options for dual sporting bikes in Ga if it says off road on the MSO or tittle thats where they stay. i would get a KLX 450 r in a minute as they can be had new for 4500 these days.

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