Post by: travis.hudson.77 on July 21, 2012, 07:33:12 AM
Post by: motoman356 on July 21, 2012, 08:11:47 AM
Post by: Jeram on July 21, 2012, 02:01:53 PM
Thinking of building a 03-05 CR250, i know that they had a fairly smooth motor........do any of you guys know if [with porting you can make these motors hit like the kx's, rm yz? Any help would be appreciated, motor builders who specialized in these?
the snapping "comming on the pipe" has very little to do with porting (and definitely not polishing!).
its all in the pipe and the power vale.
but keep in mind that coming on the pipe hard is not necessarily a symbol of faster. it just means that it has a torque curve which has no gaping holes in it.
Although there are some gains to be had via porting, generally the 2000+ CR's are already fairly good so you will only gain a couple hp here and there throughout the range depending on what you do.
Post by: metal_miracle on July 21, 2012, 02:21:50 PM
Its that the crank case on 02+ had a too much crank volume, compare to the older models.
and that the power band that honda vent for whit the crank case motors. resulting in a no bottom, no top end power curve
If motor is broken i would get an older engine 2001 and downwards
Post by: tweetakt on July 21, 2012, 02:56:16 PM
The thing really rips. When it hits the power you better be holding on.
Not much bottom, good top end, tons of mid. I used to think it felt electric untill I rolled my KTM.
Post by: Stusmoke on July 22, 2012, 10:20:11 AM
Other than that basically what Jeram said. My 01 CR125 uses some fancy ass doo dad that controls how open the exhaust ports are at certain RPM I'd wager the 250s use the same thing. I can't speak for whether or not its tuneable. Other than that, slap on a pipe jet it to perfection grab some reeds and rev it too the moon. Do all that and it should hit you with enough force to sit you on your arse
Post by: Jeram on July 22, 2012, 11:44:24 AM
the PV controller is made by companies such as Zeeltronic.
but unless your modifying your motor theres not much point.
just keep the mods simple and enjoy your reliable, mid range powerhorse of a motor!
Post by: oppenheimer77us on July 23, 2012, 05:22:44 AM
I am in the process of a build on this 2006 CR250R for moto and have done a lot of research on what other folks have done with the engine setup (the common complaint with late model CR's was the lack of bottom end snap and inability to properly jet the stock Mikuni). I have come to the conclusion that the best mod is to replace the stock mikuni with a keihin PKW airstryker 38 and this will be my next purchase. I'm starting to regret the money I've already spent on the mikuni at this point. When I rebuild the engine I'm also going to have some cylinder/head work done and bump the compression a bit. This is probably all I'm going to get done and with the other mods should be all the engine I will need.
Post by: travis.hudson.77 on July 23, 2012, 08:21:58 PM
Post by: Stusmoke on July 24, 2012, 07:39:28 AM
I would choose a 2005-2007 model CR as a starting point, the last incarnation of the CR model. This bike has many strong points; light weight, it's an excellent neutral handler, has good suspension, and is just a blast to ride. My 2006 is bone stock engine wise with the exception of an FMF fatty and silencer, v-force reed and a JD jet kit and I like these mods.
I am in the process of a build on this 2006 CR250R for moto and have done a lot of research on what other folks have done with the engine setup (the common complaint with late model CR's was the lack of bottom end snap and inability to properly jet the stock Mikuni). I have come to the conclusion that the best mod is to replace the stock mikuni with a keihin PKW airstryker 38 and this will be my next purchase. I'm starting to regret the money I've already spent on the mikuni at this point. When I rebuild the engine I'm also going to have some cylinder/head work done and bump the compression a bit. This is probably all I'm going to get done and with the other mods should be all the engine I will need.
Thanks Guys! This is all very useful, the last two stroke i had was a 05" yz 250 and before that a 03' KX 250 that i raced in the A class......but i thought the Honda would be a fun one to build, im done with 450's.
Please post up a thread on your build with photos, we all love reading custom jobs
Post by: travis.hudson.77 on July 25, 2012, 07:24:45 PM
Travis.
Post by: captmoto on July 29, 2012, 01:26:03 AM
.025 to .030 milled from the base of the cylinder or have RB Designs or Eric Gore mill the head for pump gas. The squish is way to big for pump gas. Milling the cylinder will give more bottom endand correct the squish volume without messing with the head.
Keihin Air Striker carb. I got mine from CarbPartsWarehouse and it came with the correct 03 carb cable. You can use a carb from a late model YZ250. The difference is the back to front length and fitment but it's not a problem either way. Either carb you won't be running the TPS.
The stock pipe seems to be the way to go with a PV Shorty on it but I am running a full PC set-up because my CR had a crushed leaky pipe.
Race gas unless you can get non ethanol gas or 50-50 to handle the slight boost in compression. I run avgas 100LL with no problems. I was running 100 street racing pump gas but it was almost $10 a gallon. Avgas is $5.50
These mods will get the bike running way better, probably the way it was intended to run but this is plenty for most people.
Good luck and keep us posted. It's cool to see whats up with other peoples CR250's.
Post by: riffraff on July 29, 2012, 01:59:05 AM
It's cool to see whats up with other peoples CR250's.
Someone stole mine last month
Post by: conbread on July 29, 2012, 03:10:30 AM
Post by: travis.hudson.77 on July 29, 2012, 07:01:58 AM
Post by: oppenheimer77us on August 01, 2012, 06:31:28 AM
Post by: dogger315 on August 01, 2012, 03:16:27 PM
to consider.
The case reed motors can be modified to make good power with a fairly decent powerband,
but it requires quite a few mods and a fair amount of money. Some of the problems have
already been identified here: Excess crankwell volume, heavy crankshaft, mild port timing,
recalcitrant power valve, Mikuni TMX, etc.
If you have your heart set on using the OE engine, I can recommend somebody that can turn
it into a match for anything out there today. Of course, the catch is the cost.
As an alternative, you could do the same thing that Mike LaRocco and others did when the RC
valved engines first showed up by switching to a 00/01 engine. Those engine drop right in to
the same engine mounts and swingarm pivot spacers. The only change required is a different
head stay. There is a company that markets a very inexpensive kit for this conversion. The
gen 3 roller with the gen 2 engine is the ultimate Honda all CR250 and is the bike Honda should
have built and marketed from 02 to 07.
Of the two, the 00 is a better choice. Eric Gorr comented in a book years ago that the 2001
engine was the best ever. That drove the price of those bikes and engines up dramatically.
What EG didn't say, is that the 2000 engine is identical except for the port timing and it comes
with the superior Keihin PWK carburetor. Additionally, both EG and Tom Morgan (probably the
two top Honda gurus still in the mix), prefer the 00 cylinder as the starting point for a race
motor - more potential. A complete used 00 engine can be bought on EBay, rebuilt, ported
and race prepped for less than the cost required to bring an 02-07 engine up to speed.
It all boils down to what your goals are. Do you want something that will match the latest SX
to the first turn, or do you just want a have some "fun" running mid pack.
Whatever you decide, good luck with it.
dogger
Post by: oppenheimer77us on August 02, 2012, 04:43:39 AM
I really have enjoyed this project, so much fun to get off a big thumper and back onto a 250 smoker. Haven't had this much fun in years.
Post by: twosmoke595 on August 02, 2012, 04:57:23 AM
I really have enjoyed this project, so much fun to get off a big thumper and back onto a 250 smoker. Haven't had this much fun in years.
[/quote]
and that my friend is what its all about
grinning from ear to ear as you ring the SOB out
Post by: travis.hudson.77 on August 02, 2012, 03:12:34 PM
Post by: travis.hudson.77 on August 04, 2012, 05:52:32 AM
Post by: luthier269 on August 04, 2012, 08:22:26 PM
Post by: Swimr2DaResQ on August 04, 2012, 11:21:46 PM
Post by: scotty dog on August 05, 2012, 11:01:41 PM
Best mod for that bike is to get a Keihin PWK carb from JD Jetting and get rid of the Mikuni TMX carb it came with! Just put a Keihin on my '02 and what a difference it made. JD setup the carb for my bike and area, it comes with an extra needle and two extra main jets! 245 bucks well spent!Thats not a bad price at all, i might have to look into that
Post by: kim wedding on August 12, 2012, 01:22:19 AM
Post by: _X_ on August 12, 2012, 01:34:25 AM
Post by: motoxr377 on August 12, 2012, 04:23:04 AM
Basically, it senses a abnormal spike in rpm and changes the timing slightly to compensate.
Post by: TMKIWI on August 12, 2012, 06:41:44 AM
Post by: gpnewhouse7 on August 13, 2012, 08:52:28 PM
I thought Hondas idea of traction control was to de-tune the engine after 2001 so it didn't have enough horsepower to lose traction.
Haha, an I don't think the traction control worked very well on my old 99 cr 250, if it wasn't wheelspinning it was wheelying lol it was fun at first but somewhat tiring in a 5 hour enduro.
Post by: oppenheimer77us on August 14, 2012, 02:34:44 AM
I thought Hondas idea of traction control was to de-tune the engine after 2001 so it didn't have enough horsepower to lose traction.
I think there is truth in this, this motor has so much power bottled up, the factory or other properly tuned CR's of the day had killer motors but were just screamers that were way hard to ride for the average joe. I really do think Honda did seriously de-tune this bike for public consumption.
Post by: metal_miracle on August 14, 2012, 03:03:04 AM
all case reed, and it was only the cr i could not get to terms whit
the pre 02 i liked better
Post by: TMKIWI on August 14, 2012, 06:45:53 AM
I have ridden ktm 250, CR 250, TM 250
all case reed, and it was only the cr i could not get to terms whit
the pre 02 i liked better
True. Nothing wrong with the power from the TM's.