rmz250 hybrid?

Discussion for swapping a KDX motor in a MX frame...
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bufftester
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Re: rmz250 hybrid?

Post by bufftester »

Thats what I was thinking too, would be sweet if the cradle just swapped over. Given that the swingarm requires no modification evidently it would make for an extremely fast build! I was going to just scrap my KDX frame when the hybrid is done, but now I may just hang on to it :hmm:
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Re: rmz250 hybrid?

Post by Julien D »

I had the same thought. With the ease of the swingarm mount, if the cradle will swap, dang. Talk about an easy 1-2-3 hybrid!
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Re: rmz250 hybrid?

Post by KDXGarage »

An NGK BR8ECM plug may have worked in it. My 2005 KX250 has the shorter plugs.
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Re: rmz250 hybrid?

Post by cole454 »

Yeah I didn't think about shorter plugs, but rotating it forward worked great. I thought about swapping the cradle over but I really did not want to hack up the kdx frame since its in great shape. Today I got the cradle tacked in. Next Iv got to make the engine mounts, once everything is tacked in place the engine will come out and ill fully weld in the craddle and mounts. Sorry no pics on today's progress but the bike is progressing right along. I was hoping to reuse the 4stroke radiators since they are larger but we ran into multiple problems with them, the kdx rads are a much easier choice. Got the general GNCC tomorrow so no time for this bike but I plan on a full days work on Sunday.
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rmz250 hybrid?

Post by cole454 »

I got allot done on the bike yesterday :grin: a few more hours in the shop it will be ready to ride. With the engine in and in the position that we wanted it I used cardboard to make temples then cut and bent the mounting brackets. I then proceeded to tack them in place, with the engine out I fully welded the brackets in place. Had to paint the welds with black spray paint :roll: but that is all we had time for, hopefully powder coat will come in the future. Image
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The stock RMZ air box mounted right up, we went ahead a put on a 200 carb we had laying around. Image
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I decided to only use the front headstay mount. Had to cut the rear mount off to get the engine in and out of the frame. Image
Only a few more things to do, looks like this bike will be done on time and raced on Sunday :grin: My dad is supposed to rebuild the front forks during the week and do any misc stuff that they can get done. Hopefully Ill have the bike together Thursday night so we will have Friday and Saturday to get any kinks worked out and do some suspension tuning. The only things left to make for the bike are the radiator mounts and brackets for the exhaust. It will be running a FMF gnarly pipe with a stock YZ250 silencer. Up to this point it looks like we are going to have just under $400 into the hole bike :supz: This time around we are just using whatever we can to get the bike together. The plastics are beat but once he gets more money saved up (or brakes it lol) he plans on replacing it with new plastics and hopefully some new custom hybrid graphics.
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Re: rmz250 hybrid?

Post by bufftester »

Looking good. How did you join the lower cradle tubes to the frame, just butt welds or did you use inserts? I have my old KDX frame that I bent the subframe on (prompting my hybrid build) and now am tempted to keep it around on the chance of reusing the cradle portion of it on a second hybrid using a kxf frame.
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Re: rmz250 hybrid?

Post by cole454 »

Inserts with rosette welds then butt welded the two.
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Re: rmz250 hybrid?

Post by bufftester »

Should have no worry of failure then. Looking forward to seeing it complete.
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Re: rmz250 hybrid?

Post by cole454 »

Yes i think it should be strong. The major downfall to this bike is the 1.98 gallon gas tank. Does anybody know an average miles per gallon of the kdx? We have never had to worry about it with the big tank on the kdx but now he will have to pit for fuel. The bike is running FMF with proper jetting and a 200 carb he also rides kinda aggressive.
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Re: rmz250 hybrid?

Post by CoronasAndChips »

I get between 18-20 MPG but I am a ham fisted new to dirt rider.
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Re: rmz250 hybrid?

Post by cole454 »

Yeah our MX 250's 2strokes could go around 35 miles on a MX sized tank so we will try to pit him somewhere around 35 miles.
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Re: rmz250 hybrid?

Post by bufftester »

I took my hybrid out for the first time this weekend (2001 KX125 frame/250 suspension 2001 220R motor). The tank starts at 2.25 gal, but after heat molding it to clear the head it's probably closer to 2 1/8 gal now. Rode a hard 33 miles of mostly loose sand/rocky singletrack and still had probably close to 1/3 of a tank left. Stock pipe/jetting, no RB mods, and a FMF Turbine Core II silencer, gearing 13/47 on an 18" rear which puts me at probably 45 miles on a full tank. On the old KDX the tank was 2.9 gals and I could get 60+, so it's in the same ballpark of around 20 mpg.
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Re: rmz250 hybrid?

Post by cole454 »

Good deal. My dads rebuilding the forks this week, I'm ready to ride this bike. We are not sure what has been dont to the suspension if they are stock or revalved. The forks have Moore tech suspension decals on them but no other info. We're guessing that if anything was done to them that it's for MX so we are rebuilding them with 5w oil to hopefully get them plush for woods. I'm ready for Friday to come around so we can do some testing on this bike. Let me know if anybody is interested in any parts off the KDX send me an email at yamahayz8570@aol.com let me know what your interested in.
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Re: rmz250 hybrid?

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Bike is done!!!!!! Just got done with it, everything was right the first time :supz: fired right up. The last bike I raced was a 07 ktm 250sx so thats what i'm used to and this bike felt very comparable, its sweet. I cant wait to get it on the trails tomorrow and so some suspension testing. I'm used to my dads stock KDX220 and i'm not sure which mod on this bike made if so crisp but its a totally different animal compared to the stock 220. Its got a FMF gnarly pipe with a stock YZ250 silencer, and a 200 tuned and jetted carb. Here are some pics of the radiator mounts and the bike as it came together. Ill post some better pics of the bike during the day tomorrow. Image

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Re: rmz250 hybrid?

Post by bufftester »

Bike looks sweet. May want to reroute the front brake line inside fork leg before heading out into the woods.
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Re: rmz250 hybrid?

Post by fuzzy »

Best 4-stroke Zook ever!
'91 KDX 200 Project $300 KDX
'95 KDX 200 Project $600 KDX
'94 WR 250 Always a project
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rmz250 hybrid?

Post by Tedh98 »

That looks great. You didn't waste any time getting that put together.

What was the size difference between the KDX carb inlet and the RMZ air boot opening?
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Re: rmz250 hybrid?

Post by cole454 »

Na didn't waste anytime lol had to get it done between races since race season has already started. Its sweet it feels like an overpowered 125!! It was so much fun getting back on a 2stroke after iv been on 450 quads lately. Ill switch the brake routing over tomorrow when I go over it and check all the fasteners after the first ride.

The carb fit right on the RMZ airbox :cool: a little tighter than normal but did not have to be modified at all.

He is still in school he will get to test ride it this afternoon once he gets here. I'm curious to see how he likes it. Here are some better pics of the bike. I have some gopro footage of me ridding it, if I can figure out how ill post a video of it on youtube then link it here.
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Re: rmz250 hybrid?

Post by cole454 »

Here is a quick video of the first ride on the bike.
http://youtu.be/KSZvPhEmMk8
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rmz250 hybrid?

Post by cole454 »

And after the race.... :cool: It rained about 2.5" the night before the race. He had only rode the bike about 10 miles Friday then raced it on Sunday. He got his best finish yet with a 5th place in 250C and 10 OA in the C class morning race. Hopefully he can put this bike on the top soon. Or I may have to lol. Only problems was that he lost his back brakes partly because of the mud but we are also going to rebuild the master cylinder

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