any 2 stroke guru's on here

[EZMOTO]

going to be stripping engine soon and wondered what parts are best for my cr 250, crank, piston, reeds and squish setup etc

going to be used for supermoto racing

mines a 98 engine

anyone got any helpfull info?

cheers guys

[MXCat]

Boyeson reeds.

[alohar1]

OEM ALL THE WAY. TRUST ME ON THIS ONE. PISTON TOO!!!!!!!!!!! Always allow a 2 stroke to warm up and jet it properly

[LJW]

OEM ALL THE WAY.

+1

[apa]

Pick up a couple of Eric Gorrs books.......great info on how to mod them your self.

I just rebuilt with a Wiseco crank (very reasonable price) and am happy with it but I will only use an OEM piston. Look into a V Force intake......more mid & top where a Boyesen set up is more for bottom mid.

[EZMOTO]

i'm after more power, what about wiseco pistons? different heads which i've seen where you can change the dome, i'm really after aftermarket performance parts to give me the most from my engine

[alohar1]

Apa is correct on the reeds. Oem is in the middle. As far as pistons they font call them siezeco for nothing. The real problem is the piston and cylinder heat up at different rates so if the piston gap is set incorrectly the piston will be too tight on warm up. And. Sieze. If you need more power get a bigger engine. A properly tuned 2smoke is the key. There is alot involved with proper setup of the carb and piston and air filter and exhaust. So all the aftermarket is fine but you better make damm sure you know how to set it up and jet properly. A proper setup bike should start 1st or 2nk kick, idle properly and should barely smoke after warmed up. There is a ton of info out there. Read and get to know how the motor works and more importanly why. With that info you will be able to get it running to perfection and know all the small changes needed on the fly.

[alohar1]

As far as forged cranks and pistons they are not needed unless your motor is reasly built. Forged vrs cast is a long time debate. Pros and cons to each. I think cast on a semi stock motor has more pros than cons as long as you do the proper maintaince and do periodical checks on the piston skirt by pulling the intake and exhaust and peaking inside the cyl and checking for cracks in the skirt. Damm I could go on for days in this subject

[EZMOTO]

As far as forged cranks and pistons they are not needed unless your motor is reasly built. Forged vrs cast is a long time debate. Pros and cons to each. I think cast on a semi stock motor has more pros than cons as long as you do the proper maintaince and do periodical checks on the piston skirt by pulling the intake and exhaust and peaking inside the cyl and checking for cracks in the skirt. Damm I could go on for days in this subject

please do, i love the 2 stroke's , while i'm not that technical i understand what mods to do and how they affect the spread of power, what sort of power should a well setup 250 produce, my bottom end is is pretty shite, but once in the power pulls very well, still on the pj carb, i heard these carbs are not to good, what is a better replacemnt carb for the cr250

[alohar1]

Well if your still on a pj that is your biggest problem. Get a pwk airstriker. Great carb and will set ya back about 2 bills. Then after you have that tuned to perfection and you want more you can work on other stuff. Give sudco a call and they will set ya up. Tell them where ya live and altitude and they should be able to get ya close on jetting. I'm out of town right now and on my iPhone but when I get back tonight I have some killer tuning sites that break it down for us simple guys to understand. Btw what bike fo you have?

[SMOKESKULL]

When you step on an already highly tuned engine, your playing with dynamite. You have to realise if you want to play you got to pay. You got to think of possable sudden siezures [unexpected] and what they cost in time and money. If you rebuild with stock specs [a new carb is cool] and add a good pipe your better off in the long run. Who cares if you smoke the competition every lap, but wind up having them pass you when you DNF from a siezure or other mechanical problem. A stock powervalve 250 can be a real handfull. KISS keep it simple stupid

[alohar1]

He has a 99 cr250 which is pre powervalve. These motors are used by the kart guys and they can pump out 58 hp!! Yes 58. I will find the website. But I would keep it stock with a pwk carb stock reed cage. If you want bottom fmf and top end pro circuit. Stock pipe for a happy medium. I always say hp wount make ya go faster but a nice properly setup suspension will!

[alohar1]

http://www.duncanracing.com/TechCent...arbJetting.pdf

[alohar1]

http://www.superkarttrackdays.com/77412.html?

[surfaccing]

i love the 98 cr 250k... heres my advice, clean it up, take it back to oem and then sell it and get a cr500! theirs ur big performance oversized 2stroke. i steped up to the cr500 off of a 98 cr250 and a 93 rm250 and i promise u it's a hell of a lot of power difference. the 250 has a 67mm piston the 500 has a 89mm piston!

just opt for the bigger bike. it's not that much heavier if u get a AF, but the steel frame is pretty heavy, but im sure u won't even notice the difference in weight

[EZMOTO]

http://www.superkarttrackdays.com/77412.html?

linky not working, but other one is great cheers!

looks like a pwk is my first port of call, there's one on ebay off a kx250 is this the type of carb i need

http://cgi.ebay.co.uk/2003-KAWASAKI-...item48351eb9b6

[alohar1]

Buy a new one. I got a used on once and it was fucked. Looked brand new and wasn't worth a shit. Trust me save yourself a headache.

[EZMOTO]

yeah i know, what u mean, i'm trying to find one in the uk, its not coming up with much :(

[EZMOTO]

what size do i need to order?

[alohar1]

I think stock on a cr250 is 36mm not positive though. Check eBay USA. Plenty new ones and just ask if they will ship to ya. And they will also install the jets and needle that ya need. You just need to find out what needle jet and jets work fir your altitude and average humidity.

[alohar1]

This is just a guess but my guess would be a DGN needle 42 pilot and 172 main.

[alohar1]

Go to www.thumpertalk.com it's a forum with and endless wealth of knowledge. They can get ya fixed up

[SMOKESKULL]

The 98 CR250 DOES have a powervalve and the motors had pvs for several years before that. I have seen 125s make 40ish HP so 58 from a 250 isnt impossable. I saw a drag race between a CR250 and CRF450R and it was pretty much a tie. Like I said before, a well tuned 250 is plenty enough power.

[SMOKESKULL]

Also the powerjet carb isnt a bad thing if its working properly. Basically its like having 2 different size carbs in one. You can tune the carb to run great at low speeds and yet still have the ability to have a good rich mixture at high speed with the powervavle open so you dont run the rick of lean sieze. Becasue people dont understand how it works it must not be good. It does have to be clean and working properly. If its old and has a lot of use, it might be better buying a newer carb. I know for a fact there lots of dirt bikes around that were bench raced and loaded with bling. Lots of show, but no one to make it go.

[alohar1]

The 98 CR250 DOES have a powervalve and the motors had pvs for several years before that. power.

you sir are correct. I stand corrected

[gixxerfrank]

OEM ALL THE WAY. TRUST ME ON THIS ONE. PISTON TOO!!!!!!!!!!! Always allow a 2 stroke to warm up and jet it properly

+10000000000 oem is the most reliable

[EZMOTO]

Also the powerjet carb isnt a bad thing if its working properly. Basically its like having 2 different size carbs in one. You can tune the carb to run great at low speeds and yet still have the ability to have a good rich mixture at high speed with the powervavle open so you dont run the rick of lean sieze. Becasue people dont understand how it works it must not be good. It does have to be clean and working properly. If its old and has a lot of use, it might be better buying a newer carb. I know for a fact there lots of dirt bikes around that were bench raced and loaded with bling. Lots of show, but no one to make it go.

mine is fine, idles good pulls clean but just before it hits the power there's a hesitation, i think it could be the pilot, as it seems to run best less than 1 turn in, ???

[SMOKESKULL]

Heres the bottom line, that carb may work perfect with a new top end! Even though it seems to run ok, the rings may worn out. Have you done a compression test?

[EZMOTO]

no really need one i know, will get one asap what is the ideal pressure my engine should be, ?

[SMOKESKULL]

Off the top of my head I think around 130.

[alohar1]

Anywhere from 200-220. If I had 180 or less I would think about new piston and rings.

[EZMOTO]

i'm going to make a pressure gauge, i heard pump 6psi and see if it holds for 10 mins is this correct

[stroke.n.smoke]

To leak test a two stroke you need to seal it up on the exhuast and intake and yes, no more than 6-8psi, but you should also do a vacuum test too, see how long it holds vacuum. These things create a vacuum in the crankcase also, check your crank seals. Anything over 185psi with throttle wide open is OK, 200+ seems a little high. You can set the motor up and more or less blue print the porting and clean it up, make sure everything is matched and set the squish up. You will have to talk to someone that knows the CR motors or is very experienced with two-strokes. There is alot going on in that motor that all works together. Wiseco pistons do expand at a greater rate than cast, therefore longer warm up time. I have never had any problems with Wiseco. Get on some stroker websites and find someone close to you and talk to them, see what they say about it. Here is a KX5 cylinder that I cleaned up and matched. I had it replated by max power. They did a good job with the chamfering of the ports after it was replated.





And the Wiseco piston with there crown coating and skirt coating, does it do anything, likely not but they never charged me for it.



Its been a couple years now and its still running great. Sometimes it is a bunch of little things that make all the difference. A programable ignition would be high on my list but then who do you get to tune it. Try Dyna ignitions, they might make a FS programable ignition for your bike or one that will fit, A complete rebuild usually gives a few more hp, get it running crisp and fresh and you will more than likely be happy with it.

[stroke.n.smoke]

Also you do have to run greater piston clearance with Wiseco than a stock cast piston. Wiseco states there clearance on the box. But with a plated cylinder that you can't make bigger, the pistons should come in the correct size, often there are A B C sized pistons for that reason. Take the cylinder to someone who can use a dial bore guage and measure it, then you can make the decision on which piston to use. Easiest possible way, go to Honda and buy a Honda piston/rings. There is alot that can go wrong with an inexperienced builder. Most of this is common knowledge for a good engine builder.

[2bitsamile]

if this is your 1st rebuild, Good idea to have an experience person help
For sure, get a shop manual and follow every step carefully. There are some possible exceptions as noted below:

wiseco specs 0.0015" min piston-cylinder clearance. Honda spec is 0.0024" to 0.0029" for that engine. Check clearance with a feeler gauge. I've installed about 5 Wiseco piston in '92- '01 cr250 and clearance was 0.002" everytime in "A" cylinders (which is the smallest). Check clearance with a feeler gauge, if not enough, lightly sand the piston until it's good (very unlikely you need to do that). So, probably no need to measure cylinder with bore guage. I'd guess the bigger clearace Honda uses means less chance of somebody cold-sieze an engine and trying to claim repair under warranty.

my '01 Honda manual says to replace piston and rings "every 7.5hrs under racing conditions". ummm no thank you, Wiseco for me.

with tighter piston-cylinder clearance, the wiseco piston lasts longer. Wiseco piston is also lighter (~190g vs 220g). Under hard use like karting or sumo, the lighter piston could melt sooner than the thicker-heavier OEM piston (ie if your main jet too lean, so be carefull).

I always use wiseco, never had any cold sieze or other problems. I feel safer not having to worry about a shattered OEM cast piston (commonly reported) and the resulting debris/damage. Wiseco will never shatter. I took a big hammer to an OEM piston and it broke into pieces. I hammered on the Wiseco and all it did was deform.

I go with ring end gap minimum of 0.011”. Honda spec is 0.016" minimum (Honda being safe, again), file ring end if needed. Wiseco recommends the ring end gap of the second ring to be larger than the first to reduce ring flutter.


I like squish on the tight side 0.035" to 0.040", stock is probably 0.060", way too much, which increases chance of detonation. Measure squish on engine before disassembly so you know how thinner to go on the base gasket/head milling to get the squish you want. Crush solder in left and right side of piston simultaneously and besure that solder is touching cylinder wall, as that's where squish is smallest. Measure distance from piston pin hole to top of old and new piston and include any difference in your calculation.

be carefull with power valve crows foot actuator arm when installing cylinder. I loosen the allen head cap screw/pinch bolt, remove the the cotter pin, and push the crow’s foot shaft down slightly below the base of the cylinder to make sure it aligns with the pin on the case. If not aligned, you will jam/smash the crow’s foot which causes the exhaust valve to bind and possibly damage the crow's foot.

[EZMOTO]

if this is your 1st rebuild, Good idea to have an experience person help
For sure, get a shop manual and follow every step carefully. There are some possible exceptions as noted below:

wiseco specs 0.0015" min piston-cylinder clearance. Honda spec is 0.0024" to 0.0029" for that engine. Check clearance with a feeler gauge. I've installed about 5 Wiseco piston in '92- '01 cr250 and clearance was 0.002" everytime in "A" cylinders (which is the smallest). Check clearance with a feeler gauge, if not enough, lightly sand the piston until it's good (very unlikely you need to do that). So, probably no need to measure cylinder with bore guage. I'd guess the bigger clearace Honda uses means less chance of somebody cold-sieze an engine and trying to claim repair under warranty.

my '01 Honda manual says to replace piston and rings "every 7.5hrs under racing conditions". ummm no thank you, Wiseco for me.

with tighter piston-cylinder clearance, the wiseco piston lasts longer. Wiseco piston is also lighter (~190g vs 220g). Under hard use like karting or sumo, the lighter piston could melt sooner than the thicker-heavier OEM piston (ie if your main jet too lean, so be carefull).

I always use wiseco, never had any cold sieze or other problems. I feel safer not having to worry about a shattered OEM cast piston (commonly reported) and the resulting debris/damage. Wiseco will never shatter. I took a big hammer to an OEM piston and it broke into pieces. I hammered on the Wiseco and all it did was deform.

I go with ring end gap minimum of 0.011”. Honda spec is 0.016" minimum (Honda being safe, again), file ring end if needed. Wiseco recommends the ring end gap of the second ring to be larger than the first to reduce ring flutter.


I like squish on the tight side 0.035" to 0.040", stock is probably 0.060", way too much, which increases chance of detonation. Measure squish on engine before disassembly so you know how thinner to go on the base gasket/head milling to get the squish you want. Crush solder in left and right side of piston simultaneously and besure that solder is touching cylinder wall, as that's where squish is smallest. Measure distance from piston pin hole to top of old and new piston and include any difference in your calculation.

be carefull with power valve crows foot actuator arm when installing cylinder. I loosen the allen head cap screw/pinch bolt, remove the the cotter pin, and push the crow’s foot shaft down slightly below the base of the cylinder to make sure it aligns with the pin on the case. If not aligned, you will jam/smash the crow’s foot which causes the exhaust valve to bind and possibly damage the crow's foot.

awesome write up, has helped me loads many thanks for sharing