Turning a KX-60 (MX) into an Enduro bike

reepicheep

Member
Apr 3, 2009
670
2
I recently went from a KLR-250 to a KDX-200 (well, 225 now) and am sold on two strokes for trail bikes. The KLR was fun as a light little street bike, but moving to the KDX meant I lost 60 pounds and gained 20 HP. I also had to do a top end rebuild on the KLR... which I thought was a lot of work but straightforward until I rebuilt the KDX top end. I laughed out loud it was so easy.

Anyway, so my 9 year outgrew the neighbors XR50 he was riding, and it was time for a new bike. Found a 2000 KX-60 (which turned out to be a 1990 KX-60, gotta love Craigs List) that wasn't running but looked more or less intact.

The stated reason the bike wasn't running was because the stator was shot, and sure enough it was. Don't buy the Kawasaki part, Ricky Stator doesn't list the KX-60 part on their site, but they do carry and sell it, and know exactly what you need. Great folks to deal with, and fantastic prices relative to stock. And really cool stickers for the kids bike as well.

The bike "with a brand new piston" of course needed a new piston as well. I mentioned this was one of those craigslist deals, right? The piston in there was clean, and in backwards, and missing a chunk of the crown, and it has pressed some tiny bit of steal wire looking bit into the head and piston. Like 1mm of circlip or something. I went with the Namura which sells cheap on ebay. It obviously isn't as good as a Weisco, but it looked a lot better then the stock Kawasaki that it replaced. Not a brand to impress your buddies with, but people that use them in both bike shops and snowmobiles seem happy with them, and I am in that camp. I tore it back down after maybe 10 hours of use, and it looks to be wearing just fine, and compression is great.

The bike came with a "PSI" aftermarket header, with what looks like an FMF silencer. Never heard of PSI before now, but apparently they are big in the snowmobile world. Whatever, somebody put a heck of a lot of welding work into that silencer, it is built up from a bunch of individual 2" wide rings of metal of varying diameters, all welded together. Lots of welds on stainless, and it looks like TIG. Really nice work. No idea if it is a woods/torque or desert/rev header, but knowing the KX-60, everything seems to be geared for rev/desert/mx/race.

Which (finally) brings me to my topic... the bike was a lot of fun for my kid around the street. Took him no time at all to find the power band...

http://www.youtube.com/watch?v=wl9Y1tU-dkA

But the tradeoffs of an MX bike became apparent on our first "40 degree muddy greasy sticky woods riding" day. That poor thing was clogged to every gill with ohio mud everywhere, to the point where it simply wasn't possible to go anywhere in 2nd gear. I suppose if you pinned the throttle, kept it in that razor thin power band, and slipped the clutch constantly you could in theory move, but that's not second gear, that's just first gear but with a burnt clutch.

Jack isn't going to race MX, we are woods riders, and we are both really excited about doing some father son Enduros this summer.

So the transformation began... how to turn a KX-60 into a mythical KDX-60. :)

It turned out pretty simple. The front sprocket went down to a 13 tooth, which is about as small as I have ever been comfortable going without undue wear and tear on the sprocket and chain. Though now that I think about it as I type this, a KX-60 is a 420 instead of a 520 chain, and only 20 or so HP, so a 12 front would probably be fine. I'm not sure what stock was, but the previous owner had a 14 tooth sprocket on there. I'll have to put a 12 tooth front on the "next order list".

I switched the rear sprocket to a 48 tooth (I think stock is 44). A little pricey at $38 or something, but it did the job.

I put in Boyesen two stage reeds in place of stock (610's), and picked up a Moose "torque spacer". Just a machined aluminum spacer that sits between the reed block and the motor to move the powerband lower in the RPM range.

Jetting on the bike is a 210 main, not sure what the slow jet is, but whatever it is it is still too rich... it'll flood when you try and start it, even cold, with any throttle or any choke.

I also repacked the exhaust... less is more for these little bikes. With insulation packed in there tight, it ran really bad (on throttle stumble). With loose insulation, it ran great. I just used fiberglass wall insulation as I had it around.

I also got a cheap Dennis Kirk IRC "kids motocross" tire, which was absolute and total junk. I ended up ruining it mounting it, which was probably for the better anyway, as the knobs on the thing were pathetic anyway, and judging by how easily the steel bead wire ripped right out of the rubber bead, I don't want it any bike my kid is on anyway. I replaced it with a Pirelli scorpion, which was a much nicer tire, and had maybe 14mm high knobs, instead of that IRC mess (maybe 7mm?).

The results were great! It pulls a lot harder, it'll wheelie in 2nd gear on pavement now, which bodes well for working through mud and woods. And I now don't have a 9 year old on a bike that will approach 60 mph wound out in 6th. Nor do I have a kid frustrated because he has a bike with a peaky little narrow powerband.

The gearing is a slam dunk, do it. I am not as sure about the torque spacer. It seems to do a pretty good job, but now the carb is back further, and the "air tube" between it and the carb is pretty tight, and slightly kinked. Also, the choke lever on the carb now interferes with the airbox, so I am going to have to do some melting / cutting to get clearance to be able to use the choke. It's the "outside the filter" part of the airbox, so not a huge deal, but it's going to take a little fabricating. A hot screwdriver to the airbox was enough to get clearance to get things to mount up if you don't use the choke (which I don't at the moment, because the bike is way too rich). I'll probably pull it apart tonight and figure out if I can just melt and bend to get enough room for the choke, or if I have to carve a hole and reseal it somehow. I could carve a hole and leave it open easily, but that would give him maybe 1-2" less "water crossing" depth before the motor has a drinking problem... on a bike as low to the ground as a KX-60 is already, I hate to give up that much.

The alternative of course would be to get him an XR 80 or something... but that is a pretty heavy bike. I think this KX-60 is lighter then the XR-50 he used to ride. And the suspension on the KX-60 is fantastic... maybe even better then my KDX. The two things that keep it from being a good enduro / woods bike is (1) narrow power band and (2) short fuel range. And two strokes are just SOOOO easy and cheap to maintain, and make such good power.

It's a shame they don't make a modern KDX-80. A KX-60 but with 80cc's, a power valve, a bigger tank with reserve, aluminum rims, and geared way low, but still about the same size as the KX-60. Not likely though, as they don't even make a modern KDX-200 now :(. I guess I'll have to wait for the direct injection two stroke servo controlled power valve barely street legal KDX-350. That'd be my dream bike.

So the KX-60 is now close, and didn't cost much to get there. $450 to buy (probably over paid, but it was before Christmas and there weren't many options). $150 or so to get running again and refresh the stickers and new rear fender, maybe another $150 to get "enduro ready" with the sprockets, reeds, and torque spacer... but the sprockets had to be replaced anyway.

It still has a small tank with shorter range, but Dad is riding right beside him with a KDX-200... I'll have to stash a siphon somewhere on my bike. I'm his reserve :). And where we ride in Ohio, running back to the truck a few times during the day is no big deal. And its still a little motor, so it does OK on fuel, just not as good as the XR-50 (which runs about a year and a half between fuel ups ;) ).

I'll post another update after our first serious woods ride.
 

reepicheep

Member
Apr 3, 2009
670
2
Oh! Almost forgot, I also did the Eric Gorr (forward motion) mod where you file some 3mm x 5mm transfer port grooves into the base of the jug. Easy job with a rat tail file and some patience. Thanks for the tip Eric! The big bore kit you did for my KDX-200 is working great!
 

helio lucas

~SPONSOR~
Jun 20, 2007
1,020
0
reepicheep, he rides very well and both will have very good times :cool:

if you read the tips from eric gorr you note that he state the base of the cylinder has to be machined 0,25mm. this will retard the timing and possible make the engine less pipey and peaky.
if you really want a smooth power band it may be possible to go further than that, maybe 0,5mm. it´s a easy and cheap job and if later you want the peak power back just put a thick gasket. in order to this modification work sometimes head machining to get the proper clearance is needed.

a restricting washer in the exhaust header where connects to the cylinder do the job pretty well. it has to be a thick one or it will melt. usually it give more power in low rpm with less hit with a exchange of high rpm power. ;)

more dificult to do and not allways work is to lengthen the header. sometimes just cut the peak power, put dips on the powerband or even make the carb fine tune very sensitive... more 50mm on lenght will shift the whole curve some 1000 rpm down the scale.
it is very time consuming to experiment with various lenghts.

do remember, in order for any mod to work, jetting is essencial.

also, try the bike with and without the reed cage spacer. it might not work with you new boyesen reeds... :cool:
 

reepicheep

Member
Apr 3, 2009
670
2
Great suggestions Helio, thank you. From what I could gather from the article, adding the grooves can be done independently of moving the ports. My thinking was that when the already aging factory plating gets too bad, I'll get the whole cylinder done... get the ports moved, nickisil replate, ports moved, etc.

Good suggestion about trying it without the torque spacer. So far, it seems to be working well with the Boyesens, but it has been too cold to do much testing...
 

helio lucas

~SPONSOR~
Jun 20, 2007
1,020
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you really could move the ports without touching the plating. if the cylinder base is machined, actually you move all the cylinder :cool:

if you plan on give it a fresh bore just consider a bigger bore. a kx 65 piston is 1.5 mm bigger.
 

reepicheep

Member
Apr 3, 2009
670
2
Update...

We now have the following modifications to the stock 1990 KX-60...

1) PSI header and what looks like a straight through FMF exhaust can (came with the bike, and seems well made and seems to work well).

2) Minor jetting tweaks (again, done by whoever put the PSI expansion chamber on the bike, they seemed to have done a good job).

3) Carb cleaned, and float height adjusted properly (with no help from my Kawasaki (Suzuki) service manual, which showed a totally wrong diagram for the carb).

4) Moose torque spacer for KX-60.

5) 48 tooth rear sprocket.

6) Bark busters.

7) Pirelli Scorpion rear tire (don't get the IRC tire from Dennis Kirk, the picture is all wrong and the tire is junk).

8) Eric Gorr suggested groove in the base of the jug (I think he called it a transfer port).

9) New clutch cable

10) New seat cover (a purple-ectomy).

11) Boyesen reeds.

12) Renthal Aluminum bars (taller then stock).

I also got to hear a stock KX-60 about a week ago. My ears are *still* ringing. It is beyond obnoxious. So now I am less annoyed at the seller of this KX-60 about misrepresenting the age of the bike by almost a decade :whoa: . This PSI exhaust (and presumably the FMF exhaust, and I wouldn't be surprised if my unmarked can was actually an FMF can) is much quieter then stock.

Note, the exhaust will make the bike run badly if you repack it and stuff it tight with insulation. If you put in the insulation loosely, it runs great. Thanks for that tip... I think somebody posted it here.

Up close and at idle, the exhaust is louder then a stock XR-50. Quieter then a stock CRF-450x. As soon as the rev's climb, and still up close, the KX-60 is about the same loudness as the XR-50. Interestingly, from about 100 yards away, and with revs higher, I think this KX-60 is *quieter* then a high revving XR-50. Probably because it is a higher frequency noise, which don't carry as well. Anyway, from a noise perspective, I think this is now a solved problem for an enduro bike. It isn't loud enough to be an annoyance to everyone around, and won't be any louder then stock 4 strokes. :cool:

The gearing was a huge improvement as well. Stock gearing the bike is set up to crack 60 MPH. My first step was to change the rear sprocket from a 44 to a 48. That made starting from a stop for a new rider and little flywheel MUCH easier, and also made it to start from a stop in awkward positions (like half way up a hill).

Our first exploratory trip on the bike right after Christmas with a badly running carb (float height wrong, and exhaust packing wrong) and too tall gearing showed the bike to be a mess in the woods... The tall gearing made the bike impossible to even get out of first gear when it started getting packed with mud or was on any kind of a hill. Very frustrating to the rider.

We haven't been back in the woods yet to fight the mud, but we spent a lot of time climbing snow mounds and riding around the house, and the bike is clearly much easier to control, and Jack says it is a LOT less frustrating.

I was happy enough with the changes that I got a 12t front sprocket to replace the 13t and take it even further. I didn't do that originally because I have heard that going from a 13 to a 12 on the front dramatically accelerates chain wear... but I thought about it, and thats a little chain on that bike (410? I forget), a low horsepower motor to begin with (15 HP tops?), and a reasonable quality non o-ring chain for it was only $25 or something in the first place. This isn't a street bike, I'll just keep a spare chain in the truck.

I'll post updates after Jack gets a chance to do some back to back testing with the 12t versus the 13t, but I think it will be a slam dunk. He's like Dad, he is more interested in going more places then just top speed.

The moose torque spacer went on fine, and appears well made, but does create some problems. It moves the carb back, at which point the choke post is blocked by the airbox. You could solve this with a cable choke conversion, or do like I did, and just get a hot knife and carve out a hole in the airbox for the choke post to operate. The hole is outside the filter element, and not that big, and almost as high on the bike as other already existing airbox holes... so I don't think it is any net lose of anything. The bike will still drown at about the same depth, and the intake volume has not changed much, and the hole is inboard of the airbox and under the tank so it's not likely to accumulate a lot of debris. If you are going down this road, I'd do the torque spacer last though... I'm sure it's helping, but I doubt it's enough to justify the fuss for mounting.

The Eric Gorr groove thingy is also an unknown. It's not like you can "un-groove" it practically, so I didn't bother to try and do a rigorous "before and after" test. I trust Eric's advice and expertise, so I just did it. It was a very easy thing to do with basic hand files, looked great, and was a lot of fun anyway. I always wanted to do hand porting anyway... it's fun to shape aluminum. So this is probably worth doing, particularly if you have the jug off anyway. The other mods Eric suggest are also no doubt valuable, but they require tools I don't have. If we need to replate the cylinder before Jack outgrows this bike, we will get it cut down and bored out. For now we just have those ports.

Bottom line is the bike is running really well and isn't fussy about temps and starts well and has great throttle response and pulls hard all the way up to the rev limit... so at worst this is a harmless mod, and I suspect it helped significantly.

The Boyesen reeds are the same... the stock parts are a wear item anyway, and the Boyesens are at least as good, likely much better, and aren't any more expensive. So drop them in and know that at worst they didn't hurt anything, and likely are helping.

The bark busters were cast off Acerbis plastic units from a friend... they survived on his XR-650 for years, and even survived a 30 mph low side on the street with only minimal scratches. So of course my 9 year old broke them on his first ride on them after we put them on the KX-60 :nener:

We have the Rocky Mountain $39 aluminum ones in a box ready to go on this weekend.

The previous owner had put on a nice set of Renthal aluminum bars as well, and they are taller then stock, which seems to help Jack quite a bit to stand up and be smooth. So that's another good mod I think.

So it's close to done now... I'll put on the 12t sprocket this weekend and post some "before and after" opinions. If I can get my KDX jetting *really* dialed in, I may get bored and see if I can dial in the KX jetting any better, but I think it's pretty good as is. Then we just need to get in some time on the trails and see how it works.

A lingering problem that I may have will be range. Thats a little fuel tank, with no reserve, and I am guessing that 2s isn't very fuel efficient. So we will have to see how far it goes on the trail between fill ups. Maybe I just swap out the petcock to one with a reserve, maybe it's small enough that the small tank will go plenty far for the kind of riding we do (all closed trail systems with gas station or truck close by). I'm on a 2 stroke as well (KDX-200), so while we try it out I'll just make sure I bring a siphon in case he runs out before I do.

We are doing the MSF Dirt class this sunday, where Jack will probably be riding an XR-80 or even a 90... that'll be a good data point for him to decide if he is a 2s or a 4s guy.

Here is Jack doing the best technical stuff we can find within 100 yards of the house with the bike modded as described above...

http://www.youtube.com/watch?v=VEZZkcNQ5qk

I expect both Jack and the bike will do well on trails, and in a father / son funduro event. It'll be fun!
 

helio lucas

~SPONSOR~
Jun 20, 2007
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indeed, the eric gorr´s book is a stupidly good on basic info. he his a great guy to provide it for free... i am glad i bought it (two of them). actually, i know this website through is book.

boyesen dual stage seem to help low end and response. with my bike they clear the jetting since i had a spot i cannot deal without make another at other point.

you can advance the ignition timing a little to get even more response and torque. some 0,5 mm on the stator (clockwise) will do the trick.

the smaller the sprocket the faster it wears, but nothing dramatic. after all this is a dirt bike with small wheels and big sprockets, chain will wear fast be it 12 or 13 thoots. ;)

that said, glad everything work well. hope you both have a great riding experience. look foward to read how things went. :cool:

BTW, great reading.
 

_JOE_

~SPONSOR~
May 10, 2007
4,697
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Good stuff! :cool: I love playing around in the snow!

My buddies little sister had one of them when I was in high school. We used to try to ride it after a couple adult beverages, it ALWAYS won. It was hilarious to watch it throw one after another off it's back. They are some peaky little suckers stock. No power down low and a bit too much up top for anone weighing over 125 lbs who's sitting on the back fender. ;) I know where there's a nice one collecting dust in the back of a garage. Hopefully it's still there in 5 years or so......
 

reepicheep

Member
Apr 3, 2009
670
2
Thank Helio... coincidentally, just last night when putting on the smaller sprocket, I realized that the timing was a little retarded, so I advanced it a little. Then I see your post this morning... According to the manual, this costs some peak power, but gives a wider power band, at least on the over rev side of the curve.

He will be riding and giving the full report.

That 60 has just about put me on my butt a couple times as well... including once going into the garage when the throttle stuck. Whee! :)
 

helio lucas

~SPONSOR~
Jun 20, 2007
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this is the first ever imported cobra to portugal, yesterday, by my house. my buddy came to show me the bike. damn, those things are fast!!! talking about fliping the a$$... ahahahah, would like to beat one up in the sand, much in the way joe did... :laugh:

reepicheep, advance the timing might produce more over rev but the main gains are below the peak. on other side it might produce a harder hit in the midrange, not allways desirable for trail riding
 

reepicheep

Member
Apr 3, 2009
670
2
Update... we pulled the torque spacer, and couldn't really tell a difference... at least not in summer. So it may have helped bottom end a bit, but I don't think it is worth the headache for the problems it causes by blocking the choke lever and kinking the tube between the airbox and carb. This was with an aftermarket pipe, maybe on the stock pipe (which is so obnoxiously loud I hope nobody is running one) it would be different.

Now the bike is running badly again for some other reason... it pulls hard then cuts out then pulls hard then cuts out. Like run 3 to 5 seconds on, a couple seconds off, several seconds on, etc. Has good spark, seems to have fuel, hmmm.... Plugs come out soaking wet. I'll (re) adjust the float height and see if I screwed that up when I was playing with the jetting.
 

reepicheep

Member
Apr 3, 2009
670
2
Well, I was searching for some other information, and found my own thread, so I figured I might as well post an update.

The torque spacer sits in a box, un-needed, un-used, and un-loved. Good riddance.

The fussy running in the previous post was sorted by yet another carb cleaning and adjustment and new plugs and gas.

Jack does very well with the bike, but where we ride (Big Rock outside Maysville Kentucky) has... well... big rocks. So while he is doing great and the KX-60 geared way down does everything needed, it only has a 14 inch front wheel. So if he hits a 5" or 6" tall rock, he has a handful... and if he hits a 7" rock, he is done for. These rocks are the norm there, not an exception, so it's limiting him on a lot of otherwise very ridable trails.

So I found the perfect mod... Sell the KX-60 and buy him a KX-80. :) I'll start another thread for that one, it needs a lot of work and I have a lot of questions.

But in terms of the upgrade... he now has a KIPS valve, front and rear disk brakes, upside down front forks, 20 more cc's (at least, it needs a new top end so it may become a 100), and a 17" front wheel. Feels about the same weight, maybe even lighter.

So we get to start over! If anyone wants to buy the KX-60 I worked over here, drop me a note. I asked my daughter (next in line for it), and she said she preferred a 4 stroke. :blah:

So in summary, the obvious stuff was what made the big difference. Put on an exhaust that doesn't offend everyone in a 3 mile radius. Gear it waaaay down. Take the time to really dial in the carbs (meaning you will probably have to rejet between summer and winter). Do the easy Eric Gorr recommended porting with a rat tail file. Pay attention to fuel mixtures and to keeping the exhaust packing loose and clean. And avoid big rocks. :)
 

helio lucas

~SPONSOR~
Jun 20, 2007
1,020
0
very good to hear you sorted things out.
the 100 cylinder is the best mod you can do to that bike, it makes it really fun. :cool:
the only problem is that the kx 80 will not make rocks any smaller ;)


BTW, i have a torque spacer for the kx 80, if you are interested :laugh:
 

CarterKraft

Member
Apr 15, 2014
2
0
Best KX60 detune thread on the net!

Well, I was searching for some other information, and found my own thread, so I figured I might as well post an update.

The torque spacer sits in a box, un-needed, un-used, and un-loved. Good riddance.

The fussy running in the previous post was sorted by yet another carb cleaning and adjustment and new plugs and gas.

Jack does very well with the bike, but where we ride (Big Rock outside Maysville Kentucky) has... well... big rocks. So while he is doing great and the KX-60 geared way down does everything needed, it only has a 14 inch front wheel. So if he hits a 5" or 6" tall rock, he has a handful... and if he hits a 7" rock, he is done for. These rocks are the norm there, not an exception, so it's limiting him on a lot of otherwise very ridable trails.

So I found the perfect mod... Sell the KX-60 and buy him a KX-80. :) I'll start another thread for that one, it needs a lot of work and I have a lot of questions.

But in terms of the upgrade... he now has a KIPS valve, front and rear disk brakes, upside down front forks, 20 more cc's (at least, it needs a new top end so it may become a 100), and a 17" front wheel. Feels about the same weight, maybe even lighter.

So we get to start over! If anyone wants to buy the KX-60 I worked over here, drop me a note. I asked my daughter (next in line for it), and she said she preferred a 4 stroke. :blah:

So in summary, the obvious stuff was what made the big difference. Put on an exhaust that doesn't offend everyone in a 3 mile radius. Gear it waaaay down. Take the time to really dial in the carbs (meaning you will probably have to rejet between summer and winter). Do the easy Eric Gorr recommended porting with a rat tail file. Pay attention to fuel mixtures and to keeping the exhaust packing loose and clean. And avoid big rocks. :)


Thanks for contributing all you have. This is the best thread I have found on making a KX60 a woods bike.
I am starting the conversion now on a 03'. I have grafted a KLX110 rear subframe on it to make it accept KX 65/KLX 110 plastics tank and seat. I now have turned to engine/drive mods, thanks again.
 

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