Mayday: 4-stroke problems

[2fitty]

hey all being a bit of a noob to the dirtbike scence my skills with the motorbicycle are pretty limited. went for a ride today after fitting new stock exhaust system, and my bike ran like a sack of shite. its a 04 kx250f, bought it wth 54 hrs on the clock and was told had been rebuilt at 25hrs, now have done bout 93 hrs. Is that a lot of hours to have done on the piston and rings? mostly used for trail riding and the odd putt around kimmys and thunder.
It sounds really strange & doesnt seem to have as much power as it did, and when you wind it on it splutters and farts then dies if you dont keep the power on, its also backifirng quite a bit on deceleration.
Dont really know much bout the compression but doesnt seem to be alot there, but saying that i dont really know what im looking for.
Any idea what id be looking at for a new piston and what ever else you do?

Anyway if anyone knows of a good bike mechanic in auckland or someone doesnt mind having alook at it for me for either cash or beers that would be awesome.

much appreciated

[Rupe]

hey all being a bit of a noob to the dirtbike scence my skills with the motorbicycle are pretty limited. went for a ride today after fitting new stock exhaust system, and my bike ran like a sack of shite. its a 04 kx250f, bought it wth 54 hrs on the clock and was told had been rebuilt at 25hrs, now have done bout 93 hrs. Is that a lot of hours to have done on the piston and rings? mostly used for trail riding and the odd putt around kimmys and thunder.
It sounds really strange & doesnt seem to have as much power as it did, and when you wind it on it splutters and farts then dies if you dont keep the power on, its also backifirng quite a bit on deceleration.
Dont really know much bout the compression but doesnt seem to be alot there, but saying that i dont really know what im looking for.
Any idea what id be looking at for a new piston and what ever else you do?

Anyway if anyone knows of a good bike mechanic in auckland or someone doesnt mind having alook at it for me for either cash or beers that would be awesome.


much appreciated

what exhaust did you have on before and why did you change it?

[4stroke]

i think he had a thread earlier about the headerpipe cracked and shit its self. to me it sounds like it wants a new plug, i know my crf ran simular to the way you described when the plaug was dieing. or shit in the carb

[Rupe]

i think he had a thread earlier about the headerpipe cracked and shit its self. to me it sounds like it wants a new plug, i know my crf ran simular to the way you described when the plaug was dieing. or shit in the carb

oh ok, maybe he should clean the carb, and hot start plunger, and check the able to suck air in and blow it out cleanly as well as the new plug.

Have a look here for a carb cleaning guide http://www.thumpertalk.com/forum/sho...d.php?t=706330

[2fitty]

new spark plug sounds a bit cheaper than a piston, will try that and try and clean the carb out, and see how i get on

[Rupe]

new spark plug sounds a bit cheaper than a piston, will try that and try and clean the carb out, and see how i get on

topend should be done around 80hrs apparently

[2fitty]

topend should be done around 80hrs apparently

so should be due soon then

[4stroke]

i always worked on about 100 hrs for pistons on the the 4 strokes that are mainly trail riden, i was told to keep going till it starts using oil on the husky lol

[barty5]

hell mines done a 100 still going mint had rings at 80

[CRF119]

If you had a hi flow exhust sytem on it befor like a FMF or Pro Circuit it may need to be re jetted to suit the stock one you just put back on. Other possible thing is to much filter oil on your filter and its sucking it in to the engine.

Would still cheeck plug you are ment to replace them when you do a top end and take the bowl off the carb to inspect for any dirt.

Make sure you are running 98 or higher fuel, prefer BP(If your not i would change your fuel and try again beforeyou pull apart anything)

[scott411]

its due for a top end, its done 75 hours and that is near the end of a life of a 250 four stroke,
but as said above, FCR carbs are renowned for sucking little bits of shit in there, also check the hotstart plunger is not sticking,

[laserracer]

i had a stainless header pipe on mine when i brought it , it had a dent in the header and all my mates said i should change it as it probably was robbing my bike of power ..which it wasn't.but finally i relented and brought a brand new steel header pipe ..Well it was harder to start and lost all its bottom end ..but improved its mid range ...hated it so have put back on the old header..goes great again

[cheese]

Just freeze your pipe to get the dent out.

[barty5]

you didnt read other thread its got holes in it hard to hold the water in to freeze it like that.

[2fitty]

have got a mate who reckons he can weld it, but will still be majorly squashed, its more of a bed downwards as if ud stod on the pipe and bent it down right in the middle of the bend, if ya get what i mean. had to take it off everytime to get to the bolts for the oil filter cover.