KDXRIDER.NET

I was fixing up the KX100 yesterday because my wife hadn't ridden it in 6 months. Carb off, clean the tank, clean the carb and air filter. It had been a while since I've run it as well.

I rode it and was reminded how weak this motor is on the bottom and mid. It runs fine, it just needs to be on the pipe to make any power. I'd like to get a bit more bottom and mid out of the motor - I'll trade 30% of the peak horsepower for 15% more at the bottom! Looking to make it more KDX like

Have RBD do the head?
Smaller carb? it has a 28 mm, I think, which looked big for the cc's
Have RBD do a divider plate in the carb?
Reeds?
Restricter in the pipe?

I don't really want to get into porting and all that. It is obvious the bike doesn't get used much, so why spend a lot of money on it. My son ought to be moving from his KLX110 to this pretty soon.



(here's a side note to parents and spouses out there- just because someone says they'd like to ride and you would like them to love to ride, doesn't mean they will love to ride. Don't buy new, buy some ragged out POS and see what happens or tell that someone to get a JOB and buy thier own):)

I bet a 33mm with a divider plate would be a hoot. Have RB cut the head to the limit for pump gas and take any restricters out of the pipe if they are there. If they are stock reeds try some 607's if they are available. Work on the jetting and find something with a little more tug on the bottom. Flywheel weight might be good as well. Won't add power but it will give the illusion with a bit more "chug" to make up for the lack of low end grunt.

I'm into posting today.but anyways-----
I read somewhere,recently too, that a KX100 has about 25 hp stock.DOG GONE.That is quite abit compared to a stock KDX200.Ain't that what you say?
Anyway, RB should be able to do what you need and then some and you might not want to get back on the other bike for awhile. Imagine tossing that much bike around in such a compact package.WOW!!!

It may well deliver 25 hp, from about 6500 to 8000 rpm. I'm too big and heavy for it.
I'm looking for 15 hp from 2500 to 7000 rpm Kind of like a 2 stroke TTR motor with a decent frame. Ain't gonna happen, but I think I can improve on what I got

mOrie-
I always thought a smaller carb would be the way to go, and some restriction in the exhaust. I'll look into reeds.

OK so you missed my point.From what I read RB Designs does things to make it happen from idle to wide open. Why take away from one when hopefully both can be had? just asking big guy

Gotcha, yeah that would be nice.

Does it have the stock pipe? If not, put it back on. I went from the stock pipe to an FMF fatty on my CR80 and is lost ALL of the power below 3/4 throttle, and had a lightswitch powerband. The stock pipe actually had decent low end power.

Get a carb divider installed. The RB carb mod seems to get good results, if he can work with such a small carb.

Don't restrict your exhaust, you will lose power, put on a shorter muffler for more bottom end power. (IIRC, a longer silencer= more back pressure which helps high RPM power with two-strokes due to the exhaust pressure waves?)


Get a set of Vforce reeds and set them to the "low tension" setting for bottom end power. I did that to my CR125 and it added a lot of low end torque (atleast according to my butt dyno). I could run it around 1/3 throttle all day long, it felt like it had 2 powerbands (atleast 2 real power spikes I could say), a small surge off idle, and then the actual powerband at high RPM.

Go one tooth down on the front sprocket or a few up on the rear for a more torquey feel.


If all else fails, get a big bore kit (and porting?) when it needs to be rebuilt.

KarlP wrote: (here's a side note to parents and spouses out there- just because someone says they'd like to ride and you would like them to love to ride, doesn't mean they will love to ride. Don't buy new, buy some ragged out POS and see what happens or tell that someone to get a JOB and buy thier own):)

That is the truth!!! My daughter moved from a TTR-125 to a KX85 after much discussion, promising to ride, "yes, I'll like it better", etc. She's ridden it probably 4-5 times in the past year and it's totally the wrong bike for her. Unfortunately, the correct bike for her exists only in imagination. So, now I've got a very nice '06 KX85 sitting in the garage that I'm having a HARD time trying to sell (we're zillions of miles away from a metropolis). After that episode my new rule is "You pay 1/2". That's working pretty well.

I sent an email to a well known fella who does head and carb modifications
He suggests adding a divider plate and milling the head a bit for a very reasonable price.
I think I'll go that route and report back what happens.

I hear you NM KDX200.

When I was a young boy I really wanted a bike. My folks would have none of it. I cut lots of lawns and finally bought a Honda Z50 and hid it in the woods near the house.
Man, I got in trouble! I've had bikes ever since, though.
Had my folks bought me a brand new bike, would things be different? Probably.

I agree. My father bought me a brand new XR100 in 2002, and I rode it once every other month for a couple years. When I actually got interested it riding, I was 170 lbs and needed a different bike. I saved up moeny and used the cash I got from cleaning up the XR real nice and selling it to buy a KDX200. From then on I rode like nuts and bought nearly all of my own parts.

KarlP wrote:I sent an email to a well known fella who does head and carb modifications
He suggests adding a divider plate and milling the head a bit for a very reasonable price.
I think I'll go that route and report back what happens.

I e-mailed a guy matching that description about working on a KX65. He suggested the divider plate. I can't remember if he suggested the head or not. I would love to hear about how it turns out of you have it done.

I would like to smooth out the transition on the 65 where it hits the powerband and the power really kicks in abruptly. I think it would be more ridable in the woods if the power grew in a more linear and smoother fashion. I haven't ridden a KX100, but the 65 is all top end - nothing, nothing, nothing, nothing, then WHAM, hang on.

My 11 year old rode a KTM65 the other day and said it was very smooth. Oh great. Those things are pricey.

Does the bike have the stock exhaust on it??? That makes a world of difference since most stock exhausts have the most low end power out of any option.

On my kids 04 KX100 I put a flywheel weight and Pro circuit 296 spark arrestor. The thing will lug and chug like a diesel.

Here's the plan
Stock exhaust $0.00
12 oz FWW $90.00
Head and carb $135.00
'95 KX125 kickstarter $80.00

TOTAL $305.00

Money well spent for, hopefully, a little bark off the bottom.

I bet a 33mm with a divider

Why would he go bigger on the carb with his intentions on bottom end? If anything you'd go smaller, but the 28mm should be fine.

Motor has no powervalve, right? It's porting/head config is taylored for high RPM by maw kaw. That's probably where you'll see the most benefit, but only so much can be done. I wonder if you could epoxy the exhaust ports to make them smaller? A good worked over carb/head will be a great start.

Do they make a 'torque' pipe for it? Also, just FYI, MORE backpressure is better for low end. Run your bike with the silencer off if you don't believe me.

FWW will not give any change in power...Just slow the motors ability to rev....Which will help your 'transition' issue. It will also help the motor 'chug' as it will keep turning over when it would otherwise stall....Especially true of the smaller motors. A lot can be done w/ the carb needle profile here too.

I was thinking that a 28mm with a divider would be too small below the divider, choking off the motor until it opened up all the ways. Your probably correct about a 33mm being too though...

Maybe a bored 28?

Smarta$$

NM....The forks from that 85 are a direct bolt on to the TTR...Vince's brother has one w/ a mildly built motor and his kid who wasn't that much into riding now loves it.