kx 80/85

fishhead

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#1
Well I was just about to spring for a ttr 125 for my son and he bummed a ride on a friends kx80 and a rm80 and thats what he wants now. I've not followed the mini scene much but I've narrowed the selection down to a kx or rm with the kx being in the lead by virtue of my familiarity with the kayaba suspension and the kawi link.

I'm going to consider a preowned unit so I'm hoping someone/ anyone can give me a bit of a rundown on the model year changes and give me a heads up if there are any dogs in the pound. I'm going to look for a recent model with the inverted forks for sure. It will be for offroad use so I plan on a flywheel weight and springs and valving for his weight and conditions plus cleaning up the jetting.

Thanks in advance for the help.
 

Chili

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#2
My son has raced a 99 KX80 for the last 2 seasons and we have been happy with the purchase. We went changed the gearing from 14/50 to 13/49 and went to some low tension carbon fibre reeds from Carbon Tech.

The only problem we had was right near the end of this season we had the pin that holds the powervalve snap right after a fresh rebuild. This of course resulted in taking out the new piston and scoring the cylinder. I learned later from Eric and Rich that this is a fairly common failure on this setup and changing that pin during a rebuild would be a wise step.
 

Midhigh

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#3
My son ride the 2001 KX 85. It has been a very good bike. I changed to front sproket from 14T to 13T. The KX is a little more beginner friendly than the RM. My son really likes it.
 

KelvinKDX

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#4
Originally posted by fishhead
... It will be for offroad use so I plan on a flywheel weight and springs and valving for his weight and conditions plus cleaning up the jetting.

Thanks in advance for the help.
If he is using it for off-road use and not racing in any cc class - you may want to look into the kx100 too.
 

fishhead

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#5
the kx100 is a bit taller than the kx 80 since the wheels are larger. a few guys run kx 100 top ends on kx80/85 bottoms in the local super mini class and some run the 2mm overbore setup.
 
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#6
Now you can get a RM100 if you wait for a used one.

I got a '97 RM80 instead of a TTR125 and I'm glad I did. Weight was plentiful and power was lacking in my opinion. And now it has electric start????? The RM has good low-end power right after the KX. If you are riding lots of trails he might like the 100 ported for low end power(what I was going to get instead of my KDX). Whats he weigh and how tall is he? I'm 5'6", 140 and the KX100 fits me good.
 

fishhead

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#7
he's 90lbs and 4'8" not quite ready for 100cc power but growing fast. not at the age where the big growth spurt hits boys. its a couple years away
 
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#8
We've run a full season's MX on a KX85 (big wheels) and not had any problems until last week. It's 2001 bike and did two successful seasons before we bought it. The previous owner left it stock except for a 51t rear sprocket for more pull out of the corners and a Pro-Circuit pipe to strengthen the mid-range.
Last week it started making odd noises and we suspected the crank wanted rebuilding. It was just about at that point but the noise was a seized water pump bearing-so its had the full rebuild anyway.
While it was stripped we noticed the power valve wasn't opening fully. They can get carboned up - so need to keep an eye on that.
Also - power valve actuator can fall apart and create a lot of damage in the clutch casing. The answer, we are told, is to overfill the oil level. It should take 650ml but most people reccomend 700 or a bit more. For best performance change piston and rings around every 12 hours racing use.
The KX seems fairly robust to us and my son loves riding it. It handles well and has good brakes. We are pleased we bought it.
 
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#9
CR85r:
Goods:
improved power from extra displacement
excellent gear ratios, shifting
effective, highly-adjustable suspension
Bigbike front disc brake, super-powerful
good balance between cornering, stability
unequaled durability, ease of maintainance

Downs:
bar bend old, changes with crashes
chain wears out too quickly
suspension on soft side for experts
seat/tank junction snags right boot
clutch fades when abused, no AOF

KX85:
Good:
Excellent turning, handling
great clutch action, light pull
Easy to flick around
smooth power delivery
great beginner/ novice mount

bad:
suspension holds back fast ones
so does the midrange motor
heaviest bike in class
pocket in seat restricts movement
gastank inlet too small for quickfills

rm85:
good:
best clutch, slick shifting
smaller, lighter kids dig shocks
more low-end than yz, cr, kx
lightest weight in class
flat tank/seat junction

bad:
Lacks top end power
fork too stiff, shock too soft
cheesiest graphics in class
slowest turning, some shake
steel brake pedal

yz85:
good:
most top-end power, good bottom/ mid
excellent suspension balance, action
excellent turning, stability
good bar bend, skinny ergonomics
great package at lowest price

bad:
Cheesiest chain stretches quickly
clutch weak, need adjust on the fly
tall seat height for shorter riders
power delivery erratic for neophytes

Ergonomically Correct
1:Yz85..............Thinnest
2:cr85..........Wide, Catch Boot
3:rm85.......Tallest, swept bars
4:kx85........Seat pocket

Fork Facts
1:yz...........Tuned for speed
2:rm...........Stiff
3:cr..............stiffest
4:kx............Softest

Shock Jocks
1:yz...............perfection
2:cr..............stiff but good
3:kx..............soft but good
4:rm.............to soft for most

Suspension sensations
1:yz..........Best balance
2:cr..........best expert
3:rm...........imbalanced
4:kx...........beginner/novice

Peak Ponies
1:yz.............22.7
2:cr.........21.8
3:rm............21
4:kx..............20.7

power spread
1:yz...........widest spread
2:cr.............soft low
3:rm...........all mid
4:kx.............no top

Turning Tables
1:kx............mindreader
2:yz............wired into CNS
3:cr............stiff fork
4:rm.......... stiff, sedated

Stability at speed
1:yz.........no headshake
2:rm.........imbalanced
3:kx.........headshake
4:cr.......... headshake

Clutch
1:rm
2:kx
3:yz
4:cr

Brakes
1:cr
2:yz
3:kx
4:rm

Best beginner/ novice
1:kx
2:rm
3:yz
4:cr

Best expert
1:yz
2:cr
3:rm
4:kx

Overall
1:yz
2:cr
3:rm
4:kx
 
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#10
He's 4'8", oh, then you might get a XR100 if he is pretty "timid" or isn't real agressive and doesn't jump a lot.

But you might go ahead and get a 80 anyway. The 80 will prepare him better for his next bike(especially if it's a two stroke or he is going to race). What does he ride now? I rode a PW80 before my RM80.



I read that test pyrofreak posted in a magizine not to long ago. They put too much down on the bike if it isn't perfect. The KX and RM are last over all but you go to a race and that is all you see.

But, like it says the KX and RM are beginners and the CR and YZ are for experts.
 

Chili

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#11
Pyro all that data and most other magazine spewed tripe is of little use in the real world. I think that all the bikes nowadays are getting so good that there is so little difference especially in the 85cc class. For reference your data shows the YZ as the best Expert bike as well as the Best overall 85cc bike, our top 10 for points in our premier 85cc class here went as follows this season.

1. KX
2. CR
3. CR
4. RM
5. KX
6. KX
7. KX
8. CR
9. CR
10. KX

You had to get to 11th before you saw a YZ. And before you assume we have no Yamaha dealers here they outnumber all other brands of bikes for dealers in my city.

Bottom line is they are all good bikes, get the one that your most comfortable with and like the dealer the best!
 

fishhead

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#12
The xr100 was on the short list with the ttr125 till we went to the last Hare Scramble and I saw how much more aggressive he'd become in the last several months. The 80 class bikes are a lot lighter than the 4strokes and they all have much better suspension so he will have to learn some throttle control but I don't see that as big a problem since I'm commited to riding with him on the easier terrain till he gets his skills up. The rm and the kx seem to do much better in the woods from what I've seen since they have power valves and made a bit more low end power although the magazines don't see it that way. The yz and cr seem to fall off the pipe more readily from what I've seen on long grades up switchbacks and the like. A ttr125 powerplant in a yz80/85 chassis would be ideal but I'm not into 10,000.00 and serious shop time to concoct a frankenbike or go the bbr route. However if a good rolling chassis came along I might rethink the deal but I'd rather ride than build bikes.

A super mini chassis and a clean running 4 stroke covers a lot of bases
 
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#14
I don't know if I'd call the TTR a power plant! LOL

Does he want a 4 stroke? He'd really miss out on fun and expirence if you got a TTR. If I had got a TTR and hopped on my KDX I'd be lost.

I was scared of the power band on my RM80 when my dad told me about it like it would make my bike flip. Hey I didn't know when I rode a PW80.

It's not that hard to ride a 80 in the woods. In fact the power can come in handy once in a while.

We put a 12 tooth instead of the 13T that was on my RM and changed the gasgets to get more low end.