my 03 kx 250/500 build

[doorslammer]

hey guys
well as things go i bought a mates 2003 kx250. A little backstory, he bought it blown up, had the suspension serviced and resprung, and rebuilt it. it go 3 laps into a race and called it quits, they put it down to a crank they didnt replace, a new set of cases and crank and it was time for round two. the second tank in and i was following and it locked up hard, it got real sketchy watching it lock up through a whoop sectionwhile trying to find an exit
anyway he was fed up with it and wanted it gone, considering it had all the suspension serviced and set-up for my weight i took it looking for another project

anyways heres the carnage of the motor, not much worht keeping







and here is where it sits now after a quick clean, should be picking up a 95 500 motor late next week if im lucky



any input, tips or ideas, im open.

cheers Toby

[The Flyin Hawaiian]

Glad to see more 03/04 KX250 conversions.

[doorslammer]

thanks flyin, you post gave a heap of useful info.
anyways i picked this up tonight.
has a little weld on the clutch cover, bore measures 86mm.



still trying to work out what pipe to use. everyone seems to be happy using a cr5 pipe with the kx section welded onto it. why isnt anyone just modifying a kx pipe.
unfortunatly i couldnt get a pipe with the motor, so i havent got a front section to weld onto a cr pipe (unless a 250 pipe will work, i doubt it but i havent checked yet)
so has anyone used a kx500 pipe? did it take much to modify?

[Marco810]

Nice looking build you got going, that 250 sure went out with a bang

I believe the K5 pipe is too high, you wouldnt be able to fit it through the frame under the shock reservoir. Ive seen pipes with the lower section of a kx5 pipe and upper section of a cr5 however. And just so you know a 250 pipe wont work with a 500, different stinger size ect

[don46]

I used a KX pipe and modded it on my first two hybrids, then started using CR pipes, performance was about the same and ease of install was much easier. JFAB modded a stock desert pipe for an aluminum framed bike, there is a post here at KXriders about it, didn't look to bad

[doorslammer]

cheers guys, going to ring around and see if i can find a busted kx5 pipe someone is willing to cut the front section off.

anyway, about to order some parts (piston, gaskets etc) but i need a set of reeds as well. just wondering if someone could identify this reed block. it has a boysen sticker on it.

is it worth it? would it be better to just get a v force or standard cage with C/F reeds?

i like the angle on it, seems to match the 250 well, hopefully it will make carby/airbox alignment easier.


cheers Guys.

ill be getting into the serious stuff soon haha

[Marco810]

Have a look through Motorrad's engine build thread, im sure you'll find the answer in there

[don46]

That is in fact a Boysen RAD valve, I have not used the Rad valve, I ave V-force on mine, but Boysen makes good stuff so I'm sure its good.

[The Flyin Hawaiian]

A problem that I see with using the Rad Valve, Im assuming that it is from the 500 engine that was in a standard 500 frame, will be that the carb will go into the shock. I tried a 04 KX250 intake with a 250 V Force 2 cage. It was still close to the shock and a bit too short. I was always afraid that the carb would pull out of the airboot. I ended up sucking a reed with the V Force 2 also and it wouldnt run right anyway. I ended up going back to the 500 reed cage with a set of Boyesen reeds and a 91-94 KDX250 intake. The KDX250 shares the same reed cage and reeds with the 500 and the intake was angled better, more clearance for the shock, and is a little longer so the carb sits in the airboot much better.

[doorslammer]

Well hit a bit of a snag, ended up fracturing both my left and right Foot, and have now got a plate in the right. After spending a month in hospital I'm finally home but still not walking...

Anyway back to the bike, those who are using cr500 pipes what muffler do you use, can I use either a cr500 or kx500 muffler. Also can I cut the front section off the 250 pipe to adapt to a cr pipe or is it too small?

Cheers

[81cr450]

use the cr500 silencer, is has to bend up where the k5 silencer just goes straight out

Hope you get healed up quick

[Suva]

OD the 250 pipe is fine, much smaller inside dia. than the 500 though

[81cr450]

If you have a lathe you could probably chuck that 250 snout up & turn the inside out to the 500's inner pipe diameter. Save hunting up one from a k5

[Suva]

don't know about the rest of you, but I still had to put a nice bend in the CR500 silencer to get 'er bolted up.  Curious if the silencer offered by Service Honda doesn't fit better, as I'm sure I lost some flow due to the bend in mine...

[The Flyin Hawaiian]

I didnt bend anything on mine. I used a homemade bracket similar to the rear bracket on a KX500 to hang mine. I wanted to be able to swap out the exhaust w/o any modifications.