Bike for the kid, RM85 vs KX100?

[Canadian Dave]

I'm looking for a trail worthy MX bike for my 12 year old. Currently he is riding a CR85 that's been bored out to a 100. The bottom end power is too flat and the power deliver too abrupt for the riding we do. I'd like to hear from parents with experience with a RM85 and KX100. My understanding is that the RM has good bottom end power and can be ridden effectively in the lower part of the power range. My understanding is that the same is true of the KX100. Can anyone shed some light on the subject?

Ideally I'd just test ride both and come to my own opinion but there are none available locally. I'll have to commit to a couple hour drive just to try one.

 

[Patman]

Did you try a flywheel weight CDave? One of those, a VForce3 and EG bore & port made some significant improvements in the amount of power, the spread and especially the delivery. The KX100 is a good option, seen plenty of trail kids on them and the RM as well. Next door kid has a 150R, much easier to ride than a CR85 but also a bit more spendy. What about a tricked out TTR125 or similar? I think Pred has one of them with YZ boingers.

 

[Canadian Dave]

Talked to a few people about the 150R. I've been warned that they can be hard to start after being stalled/dropped. I had a line on one with a Rekluse, which would all but cure the stalling problem, but it came and went before I could get my hands on it. I looked into a RMZ/KLX 125. Out of the CRF, TTR and RMZ/KLX 125s they appear to be the easiest to modify. The motor is out of a 200cc duel sport bike so increasing the displacement should be straightforward. RM and KX forks are a direct bolt on and a KX swing arm will bolt on after you enlarge the mounting holes and make a couple simple spacers. The KX shock is a direct bolt on as well. Problem is you end up with a fairly well suspended bike that is still heavy . . . . . top heavy at that. I can't help but think a light, well suspended 85 or 100 with a power-valved engine is the way to go. I'd love to hear someone tell me I'm mistaken though. I have little experience with kids play bikes so maybe a TTR or similar would be a better trail bike for a semi aggressive 12 year old?

I've added steal clutch plates to increase the flywheel affect, dialed the jetting, installed a Fatty pipe and added a couple teeth on the back but its still not where it needs to be.

I know the FFW and reeds would smoothen the power, and I am tempted to give them a try before going to a different bike, but watching my son ride he really needs more bottom end as he likes to lug the engine below the power band then open it up once the trail widens out. From my experience with bigger bikes, I don’t think the results would be dramatic enough for what I’m hoping for. Developing that riding style is my fault, that's the way I ride and he is trying to emulate what I do. Maybe a better idea would be for him to keep the CR and just buy myself a 125? :)

I have a CR rolling chassis as well so I've thrown around the idea of doing a CRF100/CR hybrid.

 

[XRpredator]

I did put YZ stuff on a TTR125. Unfortunately it only worked for a year for the kid, as he's become quite large. I'm not sure I'd recommend putting the YZ rear suspension on, but I made it work, but I'm still having brake issues. Ideally I'd like to put a later YZ125 master cylinder on the back brake so I don't have to worry about the remote resevoir. The front bolts up nice and easy, the back took some time.

we'll keep it around, though, as my daughter may someday decide again she'd like to ride. For now, it's our playbike.

 

[biglou]

Dave-I was amazed at what this little bike could do:

This thing hauled my fat ass up the hills at Wardy's with surprising ease.

The thread with the entire list of mods is here: http://www.dirtrider.net/forums3/showthread.php?t=129764&referrerid=19516

But you can probably pick out the important ones from the list rather than going all out like I did. Big bore kit, pipe, frame cradle, rear spring and YZ80/85 forks would really wake up a TTR125. And super easy to start.

That said, I've ridden RR's CRF150R, and it is an amazing little bike. And he starts his by hand when it's cold (seriously). I never had any experience with a hot restart, so I can't comment on that.

 

[Wolf]

Dave, we have a CR 85 and had similar problems. Eric Gorr took a millimeter of the top and ported it, the thing is absolutely perfect, with more low end than the RM (tried it).
We are running steel clutch plates, jetted it, and are still running the stock pipe.
Totally reversable too, as you you need to do is ad a thicker gasket if so desired.

 

[Matt Fisher]

The KX100 is a great little bike with a reasonably smooth powerband. Slap a flywheel weight on there and have a blast. You'll spend much less money and have virtually no time/headache delays than a totally modified or hybrid bike.