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08 KX250F - low compression, won't start

berno929 Posts: 15 Joined: 9/29/2009 Location: , CAN	10/14/2009 2:56 PM berno929 wrote: I have a 2008 KX250F. So I was trail riding on a beautiful day and came across innocent looking wet dirt... So I decided to make it through but there was water underneath the top soil and the rear end quickly sank. The rear wheel was pretty much completely in mud but everything else was out as the subframe was on a dryer part... So I called up friends and we dug it out... Kickstarted it and ran great all the way back home - I atually stopped at a friend's house and restarted the bike on my way home. Then I washed the bike. I got geared up for a ride on the following day; started kicking.. got it fired up - then it made a weird sound on a revolution, then was fine for 5 more seconds, then it made that weird sound again and stopped... Wouldn't start - making backfires... So I checked the carb and timing - everything looked fine. I thought the vavle clearance was too tight but the team manager at Motosport Kawi (got the bike from them) told me that they were fine at 0.005. So I had the camshafts taken off- put them back on but then after making the engine turn a few times 2 of the valves were a bit too tight. I was with my father and we decided to try and start it anyways... but then as I was kicking there was oil leaking from the hose that connects behind the clutch. It still backfired... The spark plug works fine- did a compression test and I only had 40 psi. So we took the cylinder head off..and the cylinder. Piston and rings are top notch as well as cylinder. Problem is there's a shitload of carbon deposit on top of the piston and where the valve heads are. The inside of the pipe is all black, too. So could a piece of carbon deposit be the problem? I put the head sideways and filled it with gas. There was the equivalent of 1 drop/5 minutes going through both exhaust valves so I take it that's OK. The deposit is quite thick and really compacted on some stuff so it couldn't have been 1 screw up deal..probably just me running the fuel screw a bit too open all summer long...? But why won't it start? Let me know if you have any ideas... berno929 wrote: I have a 2008 KX250F. So I was trail riding on a beautiful day and came across innocent looking wet dirt... So I decided to make it through but there was water underneath the top soil and the rear end quickly sank. The rear wheel was pretty much completely in mud but everything else was out as the subframe was on a dryer part... So I called up friends and we dug it out... Kickstarted it and ran great all the way back home - I atually stopped at a friend's house and restarted the bike on my way home. Then I washed the bike. I got geared up for a ride on the following day; started kicking.. got it fired up - then it made a weird sound on a revolution, then was fine for 5 more seconds, then it made that weird sound again and stopped... Wouldn't start - making backfires... So I checked the carb and timing - everything looked fine. I thought the vavle clearance was too tight but the team manager at Motosport Kawi (got the bike from them) told me that they were fine at 0.005. So I had the camshafts taken off- put them back on but then after making the engine turn a few times 2 of the valves were a bit too tight. I was with my father and we decided to try and start it anyways... but then as I was kicking there was oil leaking from the hose that connects behind the clutch. It still backfired... The spark plug works fine- did a compression test and I only had 40 psi. So we took the cylinder head off..and the cylinder. Piston and rings are top notch as well as cylinder. Problem is there's a shitload of carbon deposit on top of the piston and where the valve heads are. The inside of the pipe is all black, too. So could a piece of carbon deposit be the problem? I put the head sideways and filled it with gas. There was the equivalent of 1 drop/5 minutes going through both exhaust valves so I take it that's OK. The deposit is quite thick and really compacted on some stuff so it couldn't have been 1 screw up deal..probably just me running the fuel screw a bit too open all summer long...? But why won't it start? Let me know if you have any ideas... Quote Last Post Only I have a 2008 KX250F. So I was trail riding on a beautiful day and came across innocent looking wet dirt... So I decided to make it through but there was water underneath the top soil and the rear end quickly sank. The rear wheel was pretty much completely in mud but everything else was out as the subframe was on a dryer part... So I called up friends and we dug it out... Kickstarted it and ran great all the way back home - I atually stopped at a friend's house and restarted the bike on my way home. Then I washed the bike. I got geared up for a ride on the following day; started kicking.. got it fired up - then it made a weird sound on a revolution, then was fine for 5 more seconds, then it made that weird sound again and stopped... Wouldn't start - making backfires... So I checked the carb and timing - everything looked fine. I thought the vavle clearance was too tight but the team manager at Motosport Kawi (got the bike from them) told me that they were fine at 0.005. So I had the camshafts taken off- put them back on but then after making the engine turn a few times 2 of the valves were a bit too tight. I was with my father and we decided to try and start it anyways... but then as I was kicking there was oil leaking from the hose that connects behind the clutch. It still backfired... The spark plug works fine- did a compression test and I only had 40 psi. So we took the cylinder head off..and the cylinder. Piston and rings are top notch as well as cylinder. Problem is there's a shitload of carbon deposit on top of the piston and where the valve heads are. The inside of the pipe is all black, too. So could a piece of carbon deposit be the problem? I put the head sideways and filled it with gas. There was the equivalent of 1 drop/5 minutes going through both exhaust valves so I take it that's OK. The deposit is quite thick and really compacted on some stuff so it couldn't have been 1 screw up deal..probably just me running the fuel screw a bit too open all summer long...? But why won't it start? Let me know if you have any ideas...
aedwards07 Posts: 167 Joined: 5/17/2008 Location: KISSIMMEE, FL	10/14/2009 3:19 PM aedwards07 wrote: Unless the carbon is holding the valve open thats not the problem.Try to ride it alittle harder to clear the carbon out. But anyway double check your valve clearances.While you have the head off pour some wd40 or something else down the intake and exhaust port and check if the valves are sealing.After 30 seconds or so if you see ANY leaking past the valve then its time to replace them and recut the seats. I have $5 saying with no compression all of a sudden and it ran that its the valve clearance. aedwards07 wrote: Unless the carbon is holding the valve open thats not the problem.Try to ride it alittle harder to clear the carbon out. But anyway double check your valve clearances.While you have the head off pour some wd40 or something else down the intake and exhaust port and check if the valves are sealing.After 30 seconds or so if you see ANY leaking past the valve then its time to replace them and recut the seats. I have $5 saying with no compression all of a sudden and it ran that its the valve clearance. Quote Last Post Only Unless the carbon is holding the valve open thats not the problem.Try to ride it alittle harder to clear the carbon out. But anyway double check your valve clearances.While you have the head off pour some wd40 or something else down the intake and exhaust port and check if the valves are sealing.After 30 seconds or so if you see ANY leaking past the valve then its time to replace them and recut the seats. I have $5 saying with no compression all of a sudden and it ran that its the valve clearance.
Slow ~ Pro Posts: 3726 Joined: 3/27/2008 Location: CAPISTRANO BEACH, CA	10/15/2009 7:03 PM Slow ~ Pro wrote: Valve adjustment... Slow ~ Pro wrote: Valve adjustment... Quote Last Post Only Valve adjustment... Without the following support, my race program would not be worthy: SERVICE HONDA ~ MTA ~ IMS ~ GPR ~ SPIDER GRIPS ~ GLEN HELEN RACEWAY ~ NO TOIL ~ FLUIDYNE ~ MAXXIS ~ FREEK RACING ~ SCVET ~ SRA ~ ENGINE ICE ~ ACERBIS
williamsmotowerx Posts: 932 Joined: 4/01/2008 Location: SAUKVILLE, WI	10/15/2009 10:36 PM williamsmotowerx wrote: You can't do a compression test on a 4 stroke dirt bike. They have auto decompression valves that don't disengage at kicking speeds. williamsmotowerx wrote: You can't do a compression test on a 4 stroke dirt bike. They have auto decompression valves that don't disengage at kicking speeds. Quote Last Post Only You can't do a compression test on a 4 stroke dirt bike. They have auto decompression valves that don't disengage at kicking speeds.
berno929 Posts: 15 Joined: 9/29/2009 Location: , CAN	10/16/2009 4:42 AM berno929 wrote: Yea I realised that... Ill re-check the valves... Thanks. berno929 wrote: Yea I realised that... Ill re-check the valves... Thanks. Quote Last Post Only Yea I realised that... Ill re-check the valves... Thanks.
motofab36 Posts: 400 Joined: 4/01/2008 Location: COWDEN, IL	10/16/2009 6:25 AM Edited Date/Time: 10/16/2009 6:26 AM motofab36 wrote: Still sounds like the rings may be worn out, did you take them off and slide them into the cylinder and check the end gap? Are you 100% sure it didn't jump time? Check the cam chain tensioner, maybe go ahead and replace it while you have it apart and also look closely at the cam chain sliders for wear or damage. The funny noise and now backfireing sounds like tensioner / timing. How much time is on this bike? motofab36 wrote: Still sounds like the rings may be worn out, did you take them off and slide them into the cylinder and check the end gap? Are you 100% sure it didn't jump time? Check the cam chain tensioner, maybe go ahead and replace it while you have it apart and also look closely at the cam chain sliders for wear or damage. The funny noise and now backfireing sounds like tensioner / timing. How much time is on this bike? Quote Last Post Only Still sounds like the rings may be worn out, did you take them off and slide them into the cylinder and check the end gap? Are you 100% sure it didn't jump time? Check the cam chain tensioner, maybe go ahead and replace it while you have it apart and also look closely at the cam chain sliders for wear or damage. The funny noise and now backfireing sounds like tensioner / timing. How much time is on this bike?
Dirt Hammer Posts: 24 Joined: 10/09/2009 Location: CALHOUN, GA	10/16/2009 8:35 AM Dirt Hammer wrote: A leakdown tester is needed to determinding the four strokes internal components. Perform a leakdown on a warm bike. Dirt Hammer wrote: A leakdown tester is needed to determinding the four strokes internal components. Perform a leakdown on a warm bike. Quote Last Post Only A leakdown tester is needed to determinding the four strokes internal components. Perform a leakdown on a warm bike. Sites for Yamaha / Kawasaki enthusiast http://dirthammers.com/
berno929 Posts: 15 Joined: 9/29/2009 Location: , CAN	10/16/2009 3:06 PM berno929 wrote: Yea at first my dad thought it was the timing but that's all good. Rings looked top notch as well as cylinder. What could be wrong with the tensioner? It pulls out when I screw the thing in and stays out... About 40 hours on the bike since I got it from the Motosport race team. berno929 wrote: Yea at first my dad thought it was the timing but that's all good. Rings looked top notch as well as cylinder. What could be wrong with the tensioner? It pulls out when I screw the thing in and stays out... About 40 hours on the bike since I got it from the Motosport race team. Quote Last Post Only Yea at first my dad thought it was the timing but that's all good. Rings looked top notch as well as cylinder. What could be wrong with the tensioner? It pulls out when I screw the thing in and stays out... About 40 hours on the bike since I got it from the Motosport race team.
davis224 Posts: 1479 Joined: 8/15/2006 Location: Cornland, IL	10/16/2009 9:40 PM Dirt Hammer wrote: A leakdown tester is needed to determinding the four strokes internal components. Perform a leakdown on a warm bike. Dirt Hammer wrote: A leakdown tester is needed to determinding the four strokes internal components. Perform a leakdown on a warm bike. davis224 wrote: bingo Quote Last Post Only davis224 wrote: bingo Quote Last Post Only bingo m http://www.myspace.com/mxdavis224 m
Cygnus Posts: 7304 Joined: 8/15/2006 Location: Hanover, CO	10/17/2009 8:28 AM Cygnus wrote: As said above you can't do a compression check on the modern 4T engine. The auto decompression will almost always give a 40PSI reading. Cygnus wrote: As said above you can't do a compression check on the modern 4T engine. The auto decompression will almost always give a 40PSI reading. Quote Last Post Only As said above you can't do a compression check on the modern 4T engine. The auto decompression will almost always give a 40PSI reading. www.olympicmx.com Yamahater
onenastynotch Posts: 116 Joined: 3/03/2007 Location: West Babylon, NY	10/21/2009 7:59 PM onenastynotch wrote: hada friends 08 similar problem....pistion was broken all the way around right above the oil ring..... onenastynotch wrote: hada friends 08 similar problem....pistion was broken all the way around right above the oil ring..... Quote Last Post Only hada friends 08 similar problem....pistion was broken all the way around right above the oil ring.....
rallendude Posts: 805 Joined: 8/17/2006 Location: Adger, AL	10/22/2009 6:44 AM rallendude wrote: 90% of the 'symptoms' you've given aren't related. The carbon you speak of sounds normal for a modern 4t running on pump gas. Forget all that. If you've got the cylinder off, which you must to be able to comment on ring condition, you need to replace all the top end gaskets anyway. At the very least, put in a new set of rings. They never seat back like they were originally. Adjust the valves. Did the team manager at Motosport check them this time while you are in the bike or did he say they were fine when he sold it to you? The oil pumping from the bottom end sound like either the engine has too much oil in it or you've got a blown head gasket, which will correct itself with new gaskets on assembly. rallendude wrote: 90% of the 'symptoms' you've given aren't related. The carbon you speak of sounds normal for a modern 4t running on pump gas. Forget all that. If you've got the cylinder off, which you must to be able to comment on ring condition, you need to replace all the top end gaskets anyway. At the very least, put in a new set of rings. They never seat back like they were originally. Adjust the valves. Did the team manager at Motosport check them this time while you are in the bike or did he say they were fine when he sold it to you? The oil pumping from the bottom end sound like either the engine has too much oil in it or you've got a blown head gasket, which will correct itself with new gaskets on assembly. Quote Last Post Only 90% of the 'symptoms' you've given aren't related. The carbon you speak of sounds normal for a modern 4t running on pump gas. Forget all that. If you've got the cylinder off, which you must to be able to comment on ring condition, you need to replace all the top end gaskets anyway. At the very least, put in a new set of rings. They never seat back like they were originally. Adjust the valves. Did the team manager at Motosport check them this time while you are in the bike or did he say they were fine when he sold it to you? The oil pumping from the bottom end sound like either the engine has too much oil in it or you've got a blown head gasket, which will correct itself with new gaskets on assembly.
motofab36 Posts: 400 Joined: 4/01/2008 Location: COWDEN, IL	10/22/2009 7:55 AM motofab36 wrote: I am still more curious about the weird sound he claims it made a couple times then it died and wont restart, only backfires. motofab36 wrote: I am still more curious about the weird sound he claims it made a couple times then it died and wont restart, only backfires. Quote Last Post Only I am still more curious about the weird sound he claims it made a couple times then it died and wont restart, only backfires.
berno929 Posts: 15 Joined: 9/29/2009 Location: , CAN	10/22/2009 8:16 AM berno929 wrote: About the valves, they were all at .13mm... one of them was actually 0.125. That's pretty much 0.005 inch. I thought that was tight because in the manual I have it says the EX have to be between .17 and .22mm ... Someone handcarved 017 on the camshaft caps so I asked him to make sure and he said to have 0.005 clearance on all 4. A friend of mine who also had an '08 kx250f told me 0.005 is correct. I'm waiting on some parts to come in before I put it back togather and I'll be busy this nect week so I dunno if I'll ahve time but I'll keep you guys posted... just so you know who 'won' haha. Thanks for the help. berno929 wrote: About the valves, they were all at .13mm... one of them was actually 0.125. That's pretty much 0.005 inch. I thought that was tight because in the manual I have it says the EX have to be between .17 and .22mm ... Someone handcarved 017 on the camshaft caps so I asked him to make sure and he said to have 0.005 clearance on all 4. A friend of mine who also had an '08 kx250f told me 0.005 is correct. I'm waiting on some parts to come in before I put it back togather and I'll be busy this nect week so I dunno if I'll ahve time but I'll keep you guys posted... just so you know who 'won' haha. Thanks for the help. Quote Last Post Only About the valves, they were all at .13mm... one of them was actually 0.125. That's pretty much 0.005 inch. I thought that was tight because in the manual I have it says the EX have to be between .17 and .22mm ... Someone handcarved 017 on the camshaft caps so I asked him to make sure and he said to have 0.005 clearance on all 4. A friend of mine who also had an '08 kx250f told me 0.005 is correct. I'm waiting on some parts to come in before I put it back togather and I'll be busy this nect week so I dunno if I'll ahve time but I'll keep you guys posted... just so you know who 'won' haha. Thanks for the help.
chubb22 Posts: 1 Joined: 10/31/2009 Location: ,	10/31/2009 9:26 PM chubb22 wrote: Had similar problem with 08 yz250 f ,started OK ran fine for approx 10 -15 minutes then started coughing + backfiring until stalling and unable to re start noticed low compression....... mechanic pulled it down ....clearances were ok however lot of carbon build up on piston and a bit of this flaked off piston and held a valve open. Cleaned up piston used air compressor to clear out carburettor also, nothing found.This all happened at around 47 hrs. Went riding and sure enough 10 min. into moto started coughing backfiring again. Pulled down a 2nd time...checked shims all OK... ,putting plug cap back noticed frayed orange wire leading to cap..This was the problem. Electrical Repaired with tiny heat shrink sleeve ........ran perfect for about another 10hrs and same problem occured only different section of the wire..... This time bought new sub wiring lead ...........120hrs later still running sweet chubb22 wrote: Had similar problem with 08 yz250 f ,started OK ran fine for approx 10 -15 minutes then started coughing + backfiring until stalling and unable to re start noticed low compression....... mechanic pulled it down ....clearances were ok however lot of carbon build up on piston and a bit of this flaked off piston and held a valve open. Cleaned up piston used air compressor to clear out carburettor also, nothing found.This all happened at around 47 hrs. Went riding and sure enough 10 min. into moto started coughing backfiring again. Pulled down a 2nd time...checked shims all OK... ,putting plug cap back noticed frayed orange wire leading to cap..This was the problem. Electrical Repaired with tiny heat shrink sleeve ........ran perfect for about another 10hrs and same problem occured only different section of the wire..... This time bought new sub wiring lead ...........120hrs later still running sweet Quote Last Post Only Had similar problem with 08 yz250 f ,started OK ran fine for approx 10 -15 minutes then started coughing + backfiring until stalling and unable to re start noticed low compression....... mechanic pulled it down ....clearances were ok however lot of carbon build up on piston and a bit of this flaked off piston and held a valve open. Cleaned up piston used air compressor to clear out carburettor also, nothing found.This all happened at around 47 hrs. Went riding and sure enough 10 min. into moto started coughing backfiring again. Pulled down a 2nd time...checked shims all OK... ,putting plug cap back noticed frayed orange wire leading to cap..This was the problem. Electrical Repaired with tiny heat shrink sleeve ........ran perfect for about another 10hrs and same problem occured only different section of the wire..... This time bought new sub wiring lead ...........120hrs later still running sweet
berno929 Posts: 15 Joined: 9/29/2009 Location: , CAN	11/1/2009 9:28 AM berno929 wrote: Well, well, well... we'll never know what was the problem... So I put everything back together as everything looked fine and it wouldnt start yesterday... didn't have time to try a lot of carb adjustments tho... tried again this morning and it fired up after a few kicks...Fired it up a few times- no problems... I'll check the wires to make sure there are no apparent problems with them and go for a ride in a bit... Thanks for the help everyone... I'm happy the bike is running again but I'm a bit disappointed not to know what was wrong... berno929 wrote: Well, well, well... we'll never know what was the problem... So I put everything back together as everything looked fine and it wouldnt start yesterday... didn't have time to try a lot of carb adjustments tho... tried again this morning and it fired up after a few kicks...Fired it up a few times- no problems... I'll check the wires to make sure there are no apparent problems with them and go for a ride in a bit... Thanks for the help everyone... I'm happy the bike is running again but I'm a bit disappointed not to know what was wrong... Quote Last Post Only Well, well, well... we'll never know what was the problem... So I put everything back together as everything looked fine and it wouldnt start yesterday... didn't have time to try a lot of carb adjustments tho... tried again this morning and it fired up after a few kicks...Fired it up a few times- no problems... I'll check the wires to make sure there are no apparent problems with them and go for a ride in a bit... Thanks for the help everyone... I'm happy the bike is running again but I'm a bit disappointed not to know what was wrong...
typhoon67 Posts: 5 Joined: 12/04/2007 Location: Spring Valley, CA	11/1/2009 10:53 PM Edited Date/Time: 11/1/2009 10:54 PM typhoon67 wrote: You can do a cranking pressure test (compression) on modern 4 stroke, you first have to remove the valve cover and wire the decompressor disengaged, then do your test, but a leakdown is much more accurate. As for valves leaking a drop or so....they should leak nothing in 5 minutes, not even a weep in one hour....this must be a 100% seal at all times or drastic performance/driveability issues will result, no leakage at valve seats is the acceptable limit on any 4 stroke engine. typhoon67 wrote: You can do a cranking pressure test (compression) on modern 4 stroke, you first have to remove the valve cover and wire the decompressor disengaged, then do your test, but a leakdown is much more accurate. As for valves leaking a drop or so....they should leak nothing in 5 minutes, not even a weep in one hour....this must be a 100% seal at all times or drastic performance/driveability issues will result, no leakage at valve seats is the acceptable limit on any 4 stroke engine. Quote Last Post Only You can do a cranking pressure test (compression) on modern 4 stroke, you first have to remove the valve cover and wire the decompressor disengaged, then do your test, but a leakdown is much more accurate. As for valves leaking a drop or so....they should leak nothing in 5 minutes, not even a weep in one hour....this must be a 100% seal at all times or drastic performance/driveability issues will result, no leakage at valve seats is the acceptable limit on any 4 stroke engine.
AMA714 Posts: 639 Joined: 12/27/2007 Location: San Antonio, TX	11/3/2009 11:34 AM AMA714 wrote: So when you put it back together did you use new gaskets, or re use the old ones? AMA714 wrote: So when you put it back together did you use new gaskets, or re use the old ones? Quote Last Post Only So when you put it back together did you use new gaskets, or re use the old ones?
berno929 Posts: 15 Joined: 9/29/2009 Location: , CAN	11/3/2009 2:02 PM berno929 wrote: New gaskets... It could have been a blown gasket I guess... I'm not really an expert so I can't tell if the old one is blown. berno929 wrote: New gaskets... It could have been a blown gasket I guess... I'm not really an expert so I can't tell if the old one is blown. Quote Last Post Only New gaskets... It could have been a blown gasket I guess... I'm not really an expert so I can't tell if the old one is blown.

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