Author Topic: 2003 KX 250 SF Conversion  (Read 169928 times)

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Offline umberto

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Re: 2003 KX 250 SF Conversion
« Reply #60 on: June 28, 2015, 08:55:01 AM »
Good news part 1:  I got the tank molded today.  I boiled water in two of my wife's big soup pots and then poured the boiled water in the stainless steel sink in my utility room.  It works very well to heat the plastic to just the right temperature to mold it.  Once I got it where I wanted it, I just poured a little cold water on it. 

Good news part 2: I put the tank on it, and added oil, antifreeze/water, gas, and gave her a few kicks.  After about 4 kicks it lit right off. 

Bad news part 1: Unfortunately, I forgot to tighten my pipe mount up, so I had to kill it.  Once I got the pipe tightened back up, it wouldn't start again.  I pulled the spark plug and sure enough: no spark.  I tried a couple other new plugs I had, but no luck.  It still has compression and the fuel is flowing. 

Call for help part 1: Does anyone have any thoughts on where to start looking?  I checked all the connections and pulled the kill switch to make sure it wasn't stuck closed.  I just don't have much experience with checking the electrical systems.

Hope for the future part 1: While it was running, it sounded pretty stout.  I can't wait to ride it.
Perhaps I have a dirt bike addiction?

03 KX 250/88 KX 525/2017 KX250F - Goliath
17 KX250F/04 KX250
04 KX 250 - Lunchbox's Bike
05 KX 125/144

Offline KXDINO

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Re: 2003 KX 250 SF Conversion
« Reply #61 on: June 28, 2015, 11:21:33 AM »
earth connections

Offline sandblaster

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Re: 2003 KX 250 SF Conversion
« Reply #62 on: June 28, 2015, 11:46:14 AM »
I have all the electrical specs here as well as some helpful hints.

http://www.oem-cycle.com/forum/viewtopic.php?f=40&t=163
The four stroke engine: That's one stroke for producing power and three for wearing the engine out.

Offline umberto

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Re: 2003 KX 250 SF Conversion
« Reply #63 on: June 28, 2015, 12:29:02 PM »
I have all the electrical specs here as well as some helpful hints.

http://www.oem-cycle.com/forum/viewtopic.php?f=40&t=163
Thank you Sandblaster, that's a big help.  I'll bust out the ohm meter and get started.  If I have a bad part, can I use the CDI or coil from a 89 and up, or am I limited to 88 only?
Perhaps I have a dirt bike addiction?

03 KX 250/88 KX 525/2017 KX250F - Goliath
17 KX250F/04 KX250
04 KX 250 - Lunchbox's Bike
05 KX 125/144

Offline sandblaster

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Re: 2003 KX 250 SF Conversion
« Reply #64 on: June 28, 2015, 01:17:17 PM »
The coil is no problem.
You might be able to use the 88 CDI but I believe the timing is different.
I think the 89 and up max out at 19 degrees at 6K rpm
The 86-88 I think max out at 15 degrees
Someone hopefully can confirm
The four stroke engine: That's one stroke for producing power and three for wearing the engine out.

Offline mixn-gas

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Re: 2003 KX 250 SF Conversion
« Reply #65 on: June 28, 2015, 08:40:39 PM »
Hey umberto the conversion looks like its coming along great,
im close to stating another build similar, 03 kx250 and 94 kx500,
i may be pestering you with questions as it goes,
just for clarification you just bought the normal cr500 fmf pipe? gnarly one or what? and then cut off the engine flange and welded on the kx one?
also is the 03 bike a good one to go with? i have the motor but havn't bought the bike yet, going to look at it tommorow.
thanks from logan

Offline umberto

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Re: 2003 KX 250 SF Conversion
« Reply #66 on: June 29, 2015, 02:03:45 AM »
Hey umberto the conversion looks like its coming along great,
im close to stating another build similar, 03 kx250 and 94 kx500,
i may be pestering you with questions as it goes,
just for clarification you just bought the normal cr500 fmf pipe? gnarly one or what? and then cut off the engine flange and welded on the kx one?
also is the 03 bike a good one to go with? i have the motor but havn't bought the bike yet, going to look at it tommorow.
thanks from logan
The pipe I used was just a standard 89 and up FMF Gnarly.  I actually used a new CR pipe, a dented used CR pipe, and the KX 500 pipe. I used the flange section of the KX pipe, and two sections from the dented pipe to lengthen the pipe 1" out where it goes towards the ignition cover, and about an inch back the other way (it was a pie shape to lay the pipe over a bit more).  The CR pipe fits without the added sections, but you do have to dent it pretty severely to get around that dang coolant transfer pipe, the reed block (it kicks back in after going around the head) and to clear the ignition cover.  I solved this by adding the sections to the pipe.  I suppose you could use section out of the KX pipe instead of buying another CR pipe, but I already had the dented pipe. 

The 03/04 is a good choice from a handling standpoint, but the 05-07 should have more room for the motor (but not handle nearly as well).  You can get the newer chassis to handle if you swap out the triple clamps to change the head angle a bit.  I didn't have any issues with room, except in the front where the head gets really close to the frame and restricts access for the radiator cross over hose.  You will have to grind the weld on the frame and relocate the bottom radiator mount.  Other than that and the tank reshaping, it's been a pretty easy swap. 

I have to thank zz3gmc, he has been a lot of help.  He completed an 04 conversion that is super clean.  I'm pretty sure I wouldn't be this far without him. 

Good luck with your conversion!
Perhaps I have a dirt bike addiction?

03 KX 250/88 KX 525/2017 KX250F - Goliath
17 KX250F/04 KX250
04 KX 250 - Lunchbox's Bike
05 KX 125/144

Offline dave916

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Re: 2003 KX 250 SF Conversion
« Reply #67 on: June 29, 2015, 03:20:41 AM »
The coil is no problem.
You might be able to use the 88 CDI but I believe the timing is different.
I think the 89 and up max out at 19 degrees at 6K rpm
The 86-88 I think max out at 15 degrees
Someone hopefully can confirm

88 is 17 degree 6k rpm/ cylmer manual, so very little differance, not sure if the wire colors vary on later kx  as the pick up coil seems to change,  internal pick up coil totally confuse me :roll:

Make sure u are kicking it over fast enough when trying for spark/   No plug in and kick it like u want to start it :-) 
I end up pulling my hair out years ago try to get spark on a cr5/  luckly i had spare cdi coils etc or i would still be there/ turned out i was not kicking it fast enought even with plug removed {no compression} :-D 

Offline umberto

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Re: 2003 KX 250 SF Conversion
« Reply #68 on: June 29, 2015, 03:38:32 AM »
Could I use the entire system (coil, cdi, ignition) from an 89 and up?  Would I need to replace the flywheel as well?  Would it fit?
Perhaps I have a dirt bike addiction?

03 KX 250/88 KX 525/2017 KX250F - Goliath
17 KX250F/04 KX250
04 KX 250 - Lunchbox's Bike
05 KX 125/144

Offline dave916

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Re: 2003 KX 250 SF Conversion
« Reply #69 on: June 29, 2015, 05:14:56 AM »
Could I use the entire system (coil, cdi, ignition) from an 89 and up?  Would I need to replace the flywheel as well?  Would it fit?

U Would  need flywheel  as well
pre 89 had the smaller ligher flywheel

88 on right



« Last Edit: January 05, 2018, 02:34:17 PM by umberto »

Offline umberto

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Re: 2003 KX 250 SF Conversion
« Reply #70 on: June 29, 2015, 06:32:28 AM »
Hopefully it doesn't come to that, but knowing I can swap up makes things a whole lot easier.  Instead of just finding 88, I can look for 89 and up K5 stuff.  Thank you dave916!
Perhaps I have a dirt bike addiction?

03 KX 250/88 KX 525/2017 KX250F - Goliath
17 KX250F/04 KX250
04 KX 250 - Lunchbox's Bike
05 KX 125/144

Offline umberto

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Re: 2003 KX 250 SF Conversion
« Reply #71 on: July 04, 2015, 07:24:10 AM »
I ran through Sandblaster's awesome trouble shooting guide, and was able to get readings on most of the stuff.  There are some differences in the 88 wiring as opposed to the wiring of the 89 and up bikes, but most of the reading came back in range.  Two things really stood out to me:

The coil read in the 1.70 to 1.80 range in OHMs from the lead wire and ground.  The guide said it was supposed to be 0.26 to 0.36 and as high as 0.50.

I could not get a reading out of the plug wire, even after removing the cap.  The wire inside the plug wire was in very bad shape.  I tested the OHM meter (a brand new Bosch unit) on the stock 03 KX 250 coil I had, and it read within the range for the plug wire on that coil.  

All the other components were in the OHM range listed.  I am pretty comfortable that the coil plug wire is frayed or broken.  I found an 88 coil on e-Bay that is $35.00 with free shipping:



Or I can go with this AMR Racing coil for $67 free shipping:



Does anyone have any experience with the AMR coil?  Should I go with a stock coil and not risk using a hotter coil?
« Last Edit: July 04, 2015, 10:28:37 AM by umberto »
Perhaps I have a dirt bike addiction?

03 KX 250/88 KX 525/2017 KX250F - Goliath
17 KX250F/04 KX250
04 KX 250 - Lunchbox's Bike
05 KX 125/144

Offline sandblaster

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Re: 2003 KX 250 SF Conversion
« Reply #72 on: July 04, 2015, 09:49:15 AM »

Does anyone have any experience with the AMR coil?  Should I go with a stock coil and not risk using a hotter coil?

Yes... The AMR kept smoking my plugs after about 2-3 minutes.
Go back to the stock coil.
I found the ad for the 88 coil.
http://www.ebay.com/itm/121641622374?item=121641622374&viewitem=&vxp=mtr

I told him his price was too high and suggested 29.99
Looks like he listened...  :-o
The four stroke engine: That's one stroke for producing power and three for wearing the engine out.

Offline umberto

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Re: 2003 KX 250 SF Conversion
« Reply #73 on: July 04, 2015, 10:26:50 AM »
Awesome, thank you for saving me a few bucks!  It's on its way to OKC.
Perhaps I have a dirt bike addiction?

03 KX 250/88 KX 525/2017 KX250F - Goliath
17 KX250F/04 KX250
04 KX 250 - Lunchbox's Bike
05 KX 125/144

Offline mixn-gas

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Re: 2003 KX 250 SF Conversion
« Reply #74 on: July 11, 2015, 08:10:19 PM »
Do you have to remould the tank for clearance?
also does the standard air boot and intake manifold fit?
-Logan
« Last Edit: July 11, 2015, 11:10:02 PM by mixn-gas »