Nov 8, 2010
142
0
hey guys got myself an 03 kx250 has aparently had a full rebuild top and bottom end its got an ankle snaping 170psi comp so i dare say its been built but its near a nightmare to kick, cold its a ******* of a thing warm not so bad, it will clutch straight away but,

imediatly i suspected reeds and as such replaced them with boyosen dual stage carbon reeds, no difference made if anything a touch worse,

its got an fmf gnarly pipe and shorty silencer runs on 32:1 which im thinking of droping to 30:1 runs b8es plugs or if they dont have the b8 i get the br8es,

the jettings not perfect im in the process of trying to tweak that but i havnt been out much to do so,

im thinking either

a) plug gap
b) magneto air gap or base timing wrong
c) maybe jetting wrong but why clutch and not cick?

where would you start looking
 

arnego2

Member
Mar 8, 2008
271
1
170psi on a newly rebuild top end isn't too good IMO. So far my numbers are around 220Psi freshly rebuild Cold and @ WOT.

Does it run? Something not very clear to me when reading through your thread.
Not running comes down to several points.
Spark, Carb, Reeds, worn crank seals also contribute to hard starting.
 

arnego2

Member
Mar 8, 2008
271
1
As I said your comp numbers are quite low for a new top-end. I think its a worn out Topend. Have a peak view into the cylinder by taking off the expansion chamber (pipe). If you see a lot of blow-by you know it old and you should measure the cylinder. Some people go as far to just throw in a new piston into a worn out jug to sell a running bike. Not saying that yours is one of those though :)

Normally the piston clearance is between 0.05mm to 0.1mm in Japanese 2 stroke engines. Everything larger than would cause a drop in the "normal" compression.
 
Nov 8, 2010
142
0
mate ive built plenty bike engines in the past im telling ya now the top end is not the reason i wouldnt have asked up on here if it was a dead top end, factory specs say a rebuild should have 170-190 odd and at around 130 odd its rebuild time, 220 psi in a 2 stroke is a really high comp ratio,

ohh and for what its worth ive had a look at this top end, its not worn at all..........


does anybody have any ideas on spark, ignition etc , other than my top ends worn ffs
 

arnego2

Member
Mar 8, 2008
271
1
Try a new spark if you haven't done that already. Manual should give you some OHM values to check you electrical components. When going through electrics clean all connection points, open them up and spray some electric cleaner into them and reconnect. '03> the bike is ten years old, dust could well be crawling into those.
 

arnego2

Member
Mar 8, 2008
271
1
Your manual should tell you the values, you need a multimeter to check those.
Not too difficult using one. I had a cdi problem once and my multimeter was easier to manage than I thought.

I found that cleaning all contact points already helps starting.
 
Nov 8, 2010
142
0
might look into the cleaning, atm im waiting for a carb kit so i can pull it down go over it top to bottom check all wiring ignition, timing rebuild the carb check reeds again etc etc and see where that gets me, i wa able to have a quick read through the manual i got and i know my plug gaps to big
 
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