yes another kx250 with kx500 engine idea

[kayx250]

I've read thru a little bit of this forum and i kinda wished i found this before.

any ways I previously aquired a 2003 kx 250 when my best friend passed away and he always wanted to bore it out and make it a raped ape so when i got it I put all the stuff i could basically get for it....v-force, pc pipe, pc silencer, uni filter, max power 285cc bore and port, shaved head, high comp piston which according to the shop netted me 50+rwhp with just the internal work and a pipe. So it was no slouch(it would pull 5th gear wheelies with no clutch or without me pulling up just a simple twist of the wrist and up it came) and after about 8 months of beating on it(also beating everybody i knew ) the transmision locked up while riding back to camp after hearing a screacthing noise. didnt feel like tearing it completly apart i took the cylinder off thiinking i could find a donor 250 engine and just swap my bored cylinder and head and piston and come to find out the engine wasnt in that great of shape(had some scarring of sand on the walls )

SO..... this is my idea get a kx500 engine fab it all up work out the kinks then bore it and port it like I did the 250 "then see what it do"  As far as I know my bike(2003) has the rear head mount like the kx500 needs so thats good, I need a cr500 pipe (some fab work), what about the carborator?? Or the air boot?? how is this hooked up or do the carbarators swap out? (I.E same demensions?) If im correct the main problem is the pipe and the swingarm needing to be trimmed down  right?

any help will be apreciated.

[kayx250]

Nobody knows any of the questions I have???

[kaw rider]

do a search.you'll find what yu are looking for.

[don46]

I'm not sure if the head stay will work, it may, you'll have to bend the tank up a bit to clear the plug, maybe one of the newer shortie plugs will give enough clearance. The swingarm does need to be narrowed, the rear motor mount will need to be bored to 17mm. The carb would work as a 38mm, but I'd bore it to a 40mm. not sure how the 03 airboot will line up, if it doesn't use the 99-02 air boot, it will bolt right up to your 03 cage plate,it works good. Using the CR pipe, you'll have to change the end that goes into the cylinder, cr goes over, kx goes in, pipe mounts and modded around the water fitting for clearance. don't know about the 03 but you can make the 02 hybrid in a weekend pretty easily.

[kaw rider]

i think bdi had a nice head stay.

[kayx250]

I'm not sure if the head stay will work, it may, you'll have to bend the tank up a bit to clear the plug, maybe one of the newer shortie plugs will give enough clearance. The swingarm does need to be narrowed, the rear motor mount will need to be bored to 17mm. The carb would work as a 38mm, but I'd bore it to a 40mm. not sure how the 03 airboot will line up, if it doesn't use the 99-02 air boot, it will bolt right up to your 03 cage plate,it works good. Using the CR pipe, you'll have to change the end that goes into the cylinder, cr goes over, kx goes in, pipe mounts and modded around the water fitting for clearance. don't know about the 03 but you can make the 02 hybrid in a weekend pretty easily.

Thanks don...thats the stuff I was looking for that wasnt in the other post id searched.  About the carb...so the stock 03 carb will work, as in get me by by starting and idling or in stock trim it will ride fine?? and about the pipe do I need to source a donor kx500 pipe to chop the end off or will the end off my 250 pipe fit in the 500 head???

[don46]

The carb will work fine, you may lose some top end, but it's not going to be to noticeable. The 250 carb is actually a little better throttle response wise than the K5 carb. You may have to taper the lower left corner of the rubber boot to fit the carb, actually you could use your 250 reed cage and boot, 03 should still be the same, I think it was 05 they changed the 250 bolt pattern. As far as the pipe, you could use the flange but it needs to be bored, as I recall the OD is OK but the ID is to small, or as you said get a donor 500 pipe. I think I used a 250 flange, chucked it up in the lathe and bored to the right ID. good luck

[BDI]

i think bdi had a nice head stay.

My head stay is for a front head stay 250.You will probably have to cut the head stay mount off of the frame and shorten it up and weld it back.