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?:confused:

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?:confused:

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/showthread.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.

[2fitty]

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)

nah just had standard exhaust and found a whole standard system for the same bike on trademe, bolted straight on, then sounded sick, always run bp 98, am guna and clean the carb this week and hope i can put it back together.i do get a bit of filter oil dribbling out the bottom of the air box, to much oil on the filter, maybe! what to do if i have some in the engine?

[2fitty]

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/showthread.php?t=706330
Cheers for the link Rupe,was real helpful, have just taken the carb out, everything looks real nasty hasnt been cleaned for a while id say.

[2fitty]

off to a great start, just cracked the bowl

[Rupe]

off to a great start, just cracked the bowl

http://cgi.ebay.com/ebaymotors/RMZ-250-KX-250f-Carburetor-Carb-carberator-FCR-37mm_W0QQcmdZViewItemQQhashZitem2a043593beQQitemZ1 80459246526QQptZMotorcyclesQ5fPartsQ5fAccessories

[2fitty]

cheers but just found 1 on trademe

[2fitty]

bikes all back together and no left over parts which is always a bonus, went for a skid in the weekend and its still backfiring, any ideas why?

[Rupe]

bikes all back together and no left over parts which is always a bonus, went for a skid in the weekend and its still backfiring, any ideas why?

Is it just when your de-accelerating?

[2fitty]

Is it just when your de-accelerating?

yep happens when i button off

[Rupe]

yep happens when i button off

Apparently according to the threads on thumpertalk it's that the pilot jet is too lean, mine did it a lot more when the hot start plunger was gunked up. I did change the pilot jet one richer but it still does it, so jus got used to it, it scares the 2stroke riders when you get up behind them!!

[2fitty]

Apparently according to the threads on thumpertalk it's that the pilot jet is too lean, mine did it a lot more when the hot start plunger was gunked up. I did change the pilot jet one richer but it still does it, so jus got used to it, it scares the 2stroke riders when you get up behind them!!

sweet as, il just deal with it then, just seems strange that its only started doing it lately.

[telliman]

to much gas in carb, valves! haha

[Rupe]

sweet as, il just deal with it then, just seems strange that its only started doing it lately.



http://www.thumpertalk.com/forum/showthread.php?t=818397&highlight=popping

[Armitage Shanks]

Apparently according to the threads on thumpertalk it's that the pilot jet is too lean, mine did it a lot more when the hot start plunger was gunked up. I did change the pilot jet one richer but it still does it, so jus got used to it, it scares the 2stroke riders when you get up behind them!!

Probably because you're $-stroke is so much louder ? Guess that does'nt quite answer the question why the 250 t-strokes are'nt alllowed to run with the 250 f-strokes , they have to go with the 450's , likewise the 125 t-strokes have to run with the 250 $-strokes ...am I the only one who get's annoyed by this ?? Where's the logic .......

[2fitty]

http://www.thumpertalk.com/forum/showthread.php?t=818397&highlight=popping

good explanations there, Know how a fart works now.cheers. Have a new header, new gaskets clean hot start plunger and carb, so it must be the jetting?
is it expensive to get fixed or even worth worirng about, would it be losing power?

[Rupe]

good explanations there, Know how a fart works now.cheers. Have a new header, new gaskets clean hot start plunger and carb, so it must be the jetting?
is it expensive to get fixed or even worth worirng about, would it be losing power?

I followed the jetting info on there, and to be honest It didn't make much differance. The parts are cheap and it's easy to change them, but I'm not really that good at jetting bikes so could work for some. To be honest I noticed most kxf seem to do it and mine didn't seem bad in comparison. done near 100hrs like it now.

[Rupe]

Probably because you're $-stroke is so much louder ? Guess that does'nt quite answer the question why the 250 t-strokes are'nt alllowed to run with the 250 f-strokes , they have to go with the 450's , likewise the 125 t-strokes have to run with the 250 $-strokes ...am I the only one who get's annoyed by this ?? Where's the logic .......

What are you getting annoyed about??? pretty sure there was a thread about 250 4t's and 2t's in the same mx class over here have a search. Not sure what the $-stroke is about either, do all my own work on bikes and so far the 4t is working out cheaper than my 2t by a small margin. Both 4t's and 2t's have there own advantages, don't get to hung up on it, ride what you want. And help the guy out who asked for it, not bitch and moan.

[laserracer]

Are you sure the exhaust header is seating properly ? could be an exhaust leak..might pay to take off the header again and compare it with your old one ..seems funny it only started doing it when you changed exhausts

[2fitty]

Are you sure the exhaust header is seating properly ? could be an exhaust leak..might pay to take off the header again and compare it with your old one ..seems funny it only started doing it when you changed exhausts

yeah pretty sure, but will double check. its exactly the same header but not all bent and cracked . no it was doing it before too , thats why i got the new header cos i found the crack in the old one and thought that mustve been the problem. but no, as long as its not losing any power and the misses isnt overtaking il tough it out.

[warewolf]

went for a skid in the weekend and its still backfiring, any ideas why?It's not necessarily a problem. It's quite common on new road-registered bikes that are set up quite lean to meet the emissions regulations. It's worse with the exhaust port air injection systems, which works as the TT thread says, adds fresh oxygen to the exhaust pipe to help complete the burn. They also have the side effect of simply diluting the nasties with lots of clean atmosphere... sneaky way to reduce the parts-per-million of bad vs good!

Many people suddenly notice it when they fit a louder exhaust, which not only amplifies the sound of the popping but can make the idle mixture leaner which makes the popping worse.

If there is no actual problem, I wouldn't bother richening the idle circuit only to get rid of the popping. But if all you did was fit another similar exhaust, I would be checking you have fitted it well and don't have any air leaks (per laserracer), not just at the headers but at all the joins. If the old one was badly beaten you could have bent mounting brackets, which are stopping the new one from mating correctly.

[2fitty]

still having dramas with me bike, backfire popping has gone to a loud crakling and when i twist the throttle sometimes bogs down and almost stalls, can anyone reccomend a good mechanic or someone who knows what they are doing, pref in the eastern auck area to sort it out, before i completley screw it up myself.
cheers guys

[4stroke]

take it down to puke to mr motorcycles, scott411 on here they'lll sort it out.

[Rupe]

still having dramas with me bike, backfire popping has gone to a loud crakling and when i twist the throttle sometimes bogs down and almost stalls, can anyone reccomend a good mechanic or someone who knows what they are doing, pref in the eastern auck area to sort it out, before i completley screw it up myself.
cheers guys

Sounds like you have an air leak at the carb, either hot start, or carb boot thing. Take it to Mr moto's or Spectrum on the Shore.

[2fitty]

cheers guys, was hoping for someone a bit closer to home, and to have it sorted by this weekend, ah well. mite try mr motorcycles then

[CookMySock]

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.Normally that means "really lean mixture". What colour is the tailpipe?

Steve

[2fitty]

Normally that means "really lean mixture". What colour is the tailpipe?

Steve

sorry steve, dont know what you mean by the colour of the tailpipe, its got the original silencer, a new header pipe 10hrs old, new gaskets and a new used carb off the same model/year bike. had to buy a new carb after i tried to fix the last one myself and stuffed it, so am keen to leave it up to someone who actually knows what they are doing.

[SS90]

sorry steve, dont know what you mean by the colour of the tailpipe, its got the original silencer, a new header pipe 10hrs old, new gaskets and a new used carb off the same model/year bike. had to buy a new carb after i tried to fix the last one myself and stuffed it, so am keen to leave it up to someone who actually knows what they are doing.

I suggest you check your valve clearances, Actually, when was the last time you did that?

If your exhaust valve is tight, it will actually remain open slightly and cause a lean mixture, as will the inlet (if it is too tight) and cause backfiring out the carb (in this case)

I can't understand why none of the contributors has suggested this.

[2fitty]

had a mate check them about 12 hrs ago, he said they were fine. thanks for the info mate

[SS90]

had a mate check them about 12 hrs ago, he said they were fine. thanks for the info mate

I am surprised, given the problems you are having, and since you have swapped carbs, and it is still the same.

What about the valves leaking (possibly damaged due to over rev at some stage), is it hard to start when hot?, the symptoms you describe sound very much like a leaking valve.

If you are able, try to get it somewhere where you can have a "leak down" test done, it is a simple test, and will let you know what the condition of your top end is like.

[Reckless]

I'm Howick same as you 2fitty if you had a 2 stroke I'd fix it for you, sounds like valves to me, but I know fuck all about 4 strokes??

But if you want someone closer to Howick John in the service dept down At Botany Honda is very good! You will be paying retail through them but he will probably tell you what he thinks is wrong if you trailer it down there and start it for him.

OH shit I just thought of Barty as well at NAR. Barty5 on here, is workshop is in Newmarket, Newmarket auto repairs I'm pretty sure! He's a four stroke man! PM him he posted on page 1 this thread!

[2fitty]

I'm Howick same as you 2fitty if you had a 2 stroke I'd fix it for you, sounds like valves to me, but I know fuck all about 4 strokes??

But if you want someone closer to Howick John in the service dept down At Botany Honda is very good! You will be paying retail through them but he will probably tell you what he thinks is wrong if you trailer it down there and start it for him.

OH shit I just thought of Barty as well at NAR. Barty5 on here, is workshop is in Newmarket, Newmarket auto repairs I'm pretty sure! He's a four stroke man! PM him he posted on page 1 this thread!

Cheers reckless, now i know who to call when my misses 125 starts playing up, have been down to botany honda and he thought it was an air leak or running to lean, but its well due for a rebuild so ive been told and am not really in the position to be paying retail for it at the mo, have been talking to barty on here also ,so am hoping we can sort something out. good to see another howicken on here, let me know if you want to go for a ride sometime. usually just ride with my misses now that my other riding mate has moved back to the mainland.