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Okay so a couple of months ago I was out riding on my old 2012 yz250f and my mate let me ride his 2002 yz250 2 stroke,  I was astounded by the power delivery and immediately fell in love, that afternoon I spent a few hours cleaning, servicing and checking out a few things on my 250f before I advertised it for sale on facebook that night. I sold my 250f and got a 2006 cr250 that has just been rebuilt but not jetted to suit or started yet until I looked at it before buying it,  I didn't wanna ride it too much incase it was running lean but it sounds crisp and pulls than a 15 year old with unlimited internet access.  I need advise on jetting it because this is my first 2 stroke what will I need to know and what will I need to do to get it jetted properly? And help will be appreciated I'll include a picture of the bike just because people like looking at bikes and so do I.

 

Screenshot_2017-07-11-14-50-10-61.png

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Fine tuning the jetting is the LAST thing you do after confirming that your 11 year old MX race engine is mechanically sound:

 

-fresh top end (piston/rings)

-fresh reeds

-silencer repacked

-crank seals not worn/leaking (crank case leakdown test)

-carb cleaned, float height adjusted, stock baseline jetting

-clean oil filter, fresh gas, premix type matched to your type of riding

-new spark plug

 

Pilot jet and needle are tuned by 'feel' for best acceleration and throttle response,

main jet can be done by reading the plug, link: http://www.braigasen.com/howtoread.htm

Edited by mlatour

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On 7/13/2017 at 9:27 AM, mlatour said:

Fine tuning the jetting is the LAST thing you do after confirming that your 11 year old MX race engine is mechanically sound:

 

-fresh top end (piston/rings)

-fresh reeds

-silencer repacked

-crank seals not worn/leaking (crank case leakdown test)

-carb cleaned, float height adjusted, stock baseline jetting

-clean oil filter, fresh gas, premix type matched to your type of riding

-new spark plug

 

Pilot jet and needle are tuned by 'feel' for best acceleration and throttle response,

main jet can be done by reading the plug, link: http://www.braigasen.com/howtoread.htm

Have confirmed that it's mechanically sound I know how it's been looked after as it was my uncles and he's anal about his maintenance and engine work.  It's just been serviced, had a spark plugs put it when it was rebuilt but the carb hasn't been cleaned. Thanks for giving me some info,  really appreciate it.  Not sure if you noticed but in that picture of the Cr it has no kick-start because it's on the 07 cr250

 

 

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Re-read my post, noticed a typo,

should read: clean and oiled air filter

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Pull the carb out and disassemble it and clean it. Note your main jet, pilot jet, slide, and needle numbers. Also, needle clip position and how many "turns out" your air screw is set at. Find out the stock #'s for your bike. Bikes are jetted stock for sea level, stock exhaust/ intake, and the stock premix ratio...etc...

Typically, you have to go leaner if you ride at altitude, changed your premix from 32:1 to 40:1 (or something like that)...or made significant exhaust/intake mods.

 

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Thanks guys! The bike isn't stock it's got a pro x piston v force 3 reeds a pro circuit platinum expansion chamber and a pro circuit shorty silencer. I'll pull the carb  off and have a play with the jetting before I take it out. It's jetted to run on 40:1 and has been in my area since it was new so I'd assume the jetting should be close to right. It's also an ex race bike so its probably not far off,  if at all.  One thing I noticed is my friends 02 yz250 can be ridden for an hour and you can still touch the expansion chamber and hold your hand on it,  this Cr after one lap on a track it'll sizzle your finger prints off,  would that mean the Cr is running a bit too lean or the yz or running rich?  This is my first 2 stroke apart from a 50 cc quad I had when I was 8 so I'll be posting on here a fair bit asking for advice. Thanks again to everyone that has replied or does in the future I really appreciate it. 

Edited by Angus Evans
I included in needed information

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