CR85 Low End Power

[motoyoyo]

My son has a new CR85 Expert.  It is overall a great bike and has strong power on top that really gets it moving quick on the track.  However, when we tried taking it on a fairly technical trail ride with lots of traction, it was a real hanfull keeping it moving.  If it ever got stopped on an uphill section there was almost no low end power caryy it up the hill.  We had to clutch it in 1st gear with no rider on board in order to get it to move at all.  Is there any way to get enough power down low on these bikes to be able to ride off road effectively, or is this just a track bike to be held wide open all the time?  Even with any mods, will it as good as a KX85 or KX100 at off road trails?

 

[flying W]

www.fmfracing.com has dyno charts for stock mini's. The CR80 dyno chart shows weak power at low RPM's compared to other minis. Based on those charts, I would say that the CR would be the worst mini for trail riding. I don't know how current the charts are, however.

The charts show the CR80 so far below other mini's at lower RPM's that it does not look like there will be any easy bolt on options that will make the bike any better than a stock KX or RM. If you stick with the CR then the first modification I would do is change the porting or get a big bore.

 

[Fark]

Oh yes. I know exactly what you are talking about. What we did for my girlfriend was go one down on the countersprocket. More low end, but a harder hit obviously. This thing will throttle wheelie in 3rd with all my weight over the front. She really rides the bike under the pipe; so I figured flywheel weights won't do her good.

I contemplated porting; but I figure if I break down the cylinder might as well go big bore. It's apart and waiting to be sent to Eric Gorr. I'll check back when the work is done, should be a few weeks to include break in.

 

[motoyoyo]

Thanks for the replies.  I figured about the same thing with the powerband on this bike.  We had the fortunate/unfortunate oportunaty to ride a 2003 KX100 on our second outing with the CR85.  Aside from being a big bore already, the KX had so much more power in the low to mid it wasn't even funny.  The top end was about even since the CR85 is really strong there.  I'm seriously considering taking a hit on my purchase and going for a new KX100.  Even with an extra $1000 in big bore, porting, pipe and other mods I don't think it would match up to the powervalve KX100 motor.  Somebody talk me out of this, or buy my bike...please.

 

[lwsmithjr]

The big bore from Eric Gorr is $300.00 with the piston kit and gaskets. And it includes porting of your choice. With that bike (we have one too) you could go for the low to mid and still have decent top. You will have to supply the labor but that's a long way from $1000.00!

 

[HiG4s]

I would start with an FMF Fatty pipe, Turbine Core II silence with spark arrestor, and FMF torque reeds. All this costs $360 MSRP, you can probably get it for less at bobscycle, chaparral, or MXsouth.

 

[motoyoyo]

I'm going to call Forward Motion today and get the scoop on the big bore and porting. With the big bore along with a Fatty pipe and torque reeds, there might be a potent little off road machine there. Thanks for the tips guys. After all I would probably be looking at another $800 or so to trade up to a new KX100 anyway. If anyone out there has actually done all this stuff to a CR80 or CR85, it would be great to here your results too.

 

[Fark]

Like someone else said above; just go with the big bore for now. With Eric's porting and the displacement boost it should exceed the power level of a KX100. Plus, it won't hurt your wallet as bad.

PS How cool will it be when the stock looking CR85 spanks those KX100's?

 

[lwsmithjr]

We did the 2mm overbore with the mid and up porting. we also have a Fatty Pipe, Power Core II, and Boyesen dual stage reeds. (We tried the Carbon Fiber reeds but that killed the low end.) My son does only MX on this bike. We didn't lose any bottom because of the overbore and it screams on top. On straights, it pulls the front wheel off the ground in 4th gear (as in, it will loop out if you aren't ready). We have not had this bike in the woods since Eric did the mods. I think it would be a hand full.

Based on this, it would be my GUESS that if you went with the big bore and low to mid porting, you would have plenty of bottom and probably not lose much on top. If you did lose some, you could get it back with the pipe. I realize my mods are not what you wanted info on, but thought it may give you some useful data in your search.

BTW: According to Eric's website, because of illness in his family, his shop is closed for a few days. (I think other threads referenced his mom having surgery)

 

[sampson]

try gearing it down an offen overlooked option!

 

[FMFHonda161]

Get an FMF Fatty and Shorty Silencer. Way mor low end!!!!!!! This would only cost $50 because it is very easy to make a homemade shorty and a really nice used Fatty is $50.

 

[Racer#213]

i just got a Fatty and TC2 in the mail. I got them from Rockymountainmc.com for under 300 with no shipping charges.

 

[flying W]

Eric Gorr can move the powerband to the lower RPM's, but I doubt he can make the powerband as wide as the other mini's that have exhaust valves.

 

[Fark]

Which have exhaust valves?

 

[motoyoyo]

The Suzuki RM 85 has a very effective power valved engine and both the KX100 and RM100 have a variation of a power valve in their engines.

 

[Francois61]

Does anyone make flywheel weights for the mini's? I installed a moose weight kit on and older RM250 and it worked great in the woods. I didn't know if they made them for the smaller machines. I've been considering the RM85 for some ocassional woods riding and didn't know if this was a good idea or not. Everyones information is very helpful. Thanks

 

[whyz]

I have a cr 100 and use to ride in the woods,when it was an 80. Excellent bike, It's a 97.Got it back from EG in May02 I believe. I got the big bore kit for 300 bucks and 35 for frieght. It's very fast,, I can lug this thing anywhere. I take turns in 3rd, I lug in 2nd, and really really lug, in first.
Wheelies in 5 gears. When you want it to go fast? Oh yeah, It will. :yeehaw:
It taught my kid to ride fast so now he has my 125 while I'm pondering on what new bike to get. I practice turns and figure 8's with cones at my house.
It's a blast to ride.Especially when I fly past other brand new 85's and they dont know. :confused: Bu ha ha ha ha..
I still have to change the topend. :think: Dang it!

 

[Francois61]

Thanks WhyZ, I'm gonna check out EG's kits and shop for a new-used mini for myself. Seems to be plenty of YZ's and RM's in my area to look at. I really like the KTM 85 but a little pricey for this project: maybe next year. One dealer I contacted regarding the KTM had already sold their known allotment for the season.

All my riding buddies have big 4 strokes with e-start which are pretty nice but I'm not quite ready for one just yet. I have some very tight woods out behind my home available to ride in and think the mini might work very well with some modifications mentioned on this forum.

I guess we can't have too many different bikes in the garage can we?

 

[tnyz80]

Try a simple sprocket change. A few more teeth on the rear sprocket makes a big difference on the 85. Much less expensive that a bore.

 

[Fark]

Steahly makes flywheel weights for mini's. How's got the website? I'd stay away from those though. A bike needs the power to rotate those in a first place. You can't store energy you don't have.

 

[Rcannon]

Originally posted by Fark
[ You can't store energy you don't have. [/B]

I never looked at it like that. This is exactly what the flywheel weights do. Thanks!!! I know it appears so obvious, but I missed the entire idea behind this.

 

[sampson]

I just got a 50 tooth sprocket for my 02cr80 ,now I just have to wait till te foot of snow melts so I can try it out!!