YZ250F fouls plugs!
- Thread starter Jon K.
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Jon K.
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- Mar 26, 2001
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Sarge; he doesn't run the choke any longer than I do. Upon cranking, we will let the bike idle on choke for 30 seconds, maybe a minute, until it starts to sound rich. Then push the choke off and let it idle for another minute. Then wack the throttle a few times before riding off.
Is wacking bad?
Sage; the air screw, accel pump, and air filter have never been touched. It cranks and runs great (when the plug is good) so we have never jacked with the fuel screw.
Actually Mike (my buddy) just traded his KDX220 in on this machine. But if he fails to crank it a few more times who knows?
Is wacking bad?
Sage; the air screw, accel pump, and air filter have never been touched. It cranks and runs great (when the plug is good) so we have never jacked with the fuel screw.
Actually Mike (my buddy) just traded his KDX220 in on this machine. But if he fails to crank it a few more times who knows?
It could also very well be a problem with the ignition system. Alot of people overlook the ignition system when chronic plug fouling problem exist. check all of the ground wires and conectors in the wiring harness. sators and cdi's can also cause these symptoms when they get warmed up(hot). Good luck hope ya get it fixed soon!
maicomotoman
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- Dec 16, 2001
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I think that they dip that air filter in a vat of 90wt at the Yamaha factory. They also ship the bike with rich jetting. I would start by cleaning that filter, and giving it a light oiling on the outside only with some good filter oil. Then, buy a fistfull of plugs and jets and a 12 pack of coolies, and go re-jet that sucker!
these things run way too rich from the box. it must run pretty bad by the sounds of it. try dropping the needle one or two positions and see the results. there is heaps of work needed in jetting mods to make these things scream, but once it is worked out the results are worth the trouble.
Fouled Plugs
Don't it suck? I have had my YZ426 for three weeks now. I bought it used from a guy in Michigan. He sent it home with me with a full tank of gas. I filled up my 5 gal gas holder with premium Conoco gasoline (thats 91 octane here in KS). After I put gas in it twice, it would foul plugs when it died. If I pulled the plug, and cleaned it, it would fire first try..but if it died.it was DONE! Pull out the sockets 'cause the plugs fouled...GUARANTEED. After pulling the plug and cleaning it three times, I went to my local Yamaha shop and asked them what was up. They asked if I was running premium gas..I said 'yeah'...I figured it would be good for the bike. The head mechanic said first thing...go to 87 octane regular fuel. He said that around here they put alcohol in the fuel or ethanol in it to bump up the octane rating. The YZF's can't handle the alcohol or ethanol (or whatever's in our premium gas) and it causes the plugs to foul. I drained the tank, put in 87 octane Amoco gas, and it hasn't happened since! Might wanna give that a try.
Grasshopper
Don't it suck? I have had my YZ426 for three weeks now. I bought it used from a guy in Michigan. He sent it home with me with a full tank of gas. I filled up my 5 gal gas holder with premium Conoco gasoline (thats 91 octane here in KS). After I put gas in it twice, it would foul plugs when it died. If I pulled the plug, and cleaned it, it would fire first try..but if it died.it was DONE! Pull out the sockets 'cause the plugs fouled...GUARANTEED. After pulling the plug and cleaning it three times, I went to my local Yamaha shop and asked them what was up. They asked if I was running premium gas..I said 'yeah'...I figured it would be good for the bike. The head mechanic said first thing...go to 87 octane regular fuel. He said that around here they put alcohol in the fuel or ethanol in it to bump up the octane rating. The YZF's can't handle the alcohol or ethanol (or whatever's in our premium gas) and it causes the plugs to foul. I drained the tank, put in 87 octane Amoco gas, and it hasn't happened since! Might wanna give that a try.
Grasshopper
Two things I found when I had a WR400 and fouled plugs like crazy when I first got it:
1. Never whack the throttle when the bike is still cold. This goes along with the plug thing - when you whack a carb with an accelerator pump it supplies an ultra rich mixture - when the plug is not up to temp it can't deal with this and fouls. Just use slow throttle applications until warmed up. I think this is a common misconception - if it starts to sputter I better blip the throttle a few times to clean it out - WRONG - with an accelerator pump carb you just made it worse.
2. Get a hotter plug (I think the stock was an "8" range, I went to "7"). This helped a bunch as it seemed like it would never self clean (at least not doing mixed trail riding). I figure Yamaha puts a plug in that will deal with full load on a hot day for a long time. I never came close to that while trail riding.
Another thing I did when it was cold was cover one radiator over - as there is no thermostat. Again - yamaha sizes the radiator for 110 degree day wide open forever. when it is 45 and you are trail riding there is waaay too much cooling - which keeps the plug cold and there you go.
I have a KTM now - has a thermostat - no plug issues.
Hope this helps - I was sooo much happier with the WR once it would reliably run.
As for jetting - I felt that you should be able to get a plug setup that will handle a pretty wide range of jetting without fouling. Tuning the jetting should be for power increases - not to just keep the bike running.
Mathew
1. Never whack the throttle when the bike is still cold. This goes along with the plug thing - when you whack a carb with an accelerator pump it supplies an ultra rich mixture - when the plug is not up to temp it can't deal with this and fouls. Just use slow throttle applications until warmed up. I think this is a common misconception - if it starts to sputter I better blip the throttle a few times to clean it out - WRONG - with an accelerator pump carb you just made it worse.
2. Get a hotter plug (I think the stock was an "8" range, I went to "7"). This helped a bunch as it seemed like it would never self clean (at least not doing mixed trail riding). I figure Yamaha puts a plug in that will deal with full load on a hot day for a long time. I never came close to that while trail riding.
Another thing I did when it was cold was cover one radiator over - as there is no thermostat. Again - yamaha sizes the radiator for 110 degree day wide open forever. when it is 45 and you are trail riding there is waaay too much cooling - which keeps the plug cold and there you go.
I have a KTM now - has a thermostat - no plug issues.
Hope this helps - I was sooo much happier with the WR once it would reliably run.
As for jetting - I felt that you should be able to get a plug setup that will handle a pretty wide range of jetting without fouling. Tuning the jetting should be for power increases - not to just keep the bike running.
Mathew
i went through two plugs right off the bat on my wr 250f. i adjusted the pilot screw to factory spec (1 3/4 turns i believe). the pilot was too rich before. it has been nine months and i am still on the same plug as when i adjusted the screw, it cured any starting troubles too.
yz250-effer
Member
- Nov 4, 2000
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Agree w/ socalwr -
Check the pilot screw for 1 3/4 turns out. I just raised the needle and backed the pilot out on my 01' according to FMF's recommendations for a ti-4 exhaust and a little extra on the pilot goes a long way. I fouled / soaked a plug on the first start up. I backed the the pilot down to 2 out ( not 2 3/4) with my original plug back in it ( 15 month old plug ) and it started right up and no problems since. I don't think they are really rich out of the box, at least the YZF's anyhow. I guess it would depend on your altitude, of course. I am around 2000 feet and ran the original plug for 15 months, and I did not even really have to change it. Good luck and NEVER flood it when it is cold.:)
Check the pilot screw for 1 3/4 turns out. I just raised the needle and backed the pilot out on my 01' according to FMF's recommendations for a ti-4 exhaust and a little extra on the pilot goes a long way. I fouled / soaked a plug on the first start up. I backed the the pilot down to 2 out ( not 2 3/4) with my original plug back in it ( 15 month old plug ) and it started right up and no problems since. I don't think they are really rich out of the box, at least the YZF's anyhow. I guess it would depend on your altitude, of course. I am around 2000 feet and ran the original plug for 15 months, and I did not even really have to change it. Good luck and NEVER flood it when it is cold.:)
Mike Hubert
Member
- Apr 22, 2001
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wfo74 - KDX to YZ250F
You said your friend went from a KDX to a YZ, I am looking at the same move, does he feel he made the correct decision? I have a 2000 KDX will all the Fredette engine and carb work, Race Tech suspension and all the other recommended stuff, I ride mainly MX so I am very seriously considering the YZ.
You said your friend went from a KDX to a YZ, I am looking at the same move, does he feel he made the correct decision? I have a 2000 KDX will all the Fredette engine and carb work, Race Tech suspension and all the other recommended stuff, I ride mainly MX so I am very seriously considering the YZ.
Jon K.
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- Mar 26, 2001
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Mike, If you have done the complete MX transformation on the KDX it should be a fairly competent MX machine.
My buddy was trying to moto on a completely stock KDX and the stock KDX suspension was hopeless on the MX track. The YZ is in a whole 'nother league!! Power, suspension, brakes, noise; the YZ has it all!!
Apples and oranges!!
If you can crank it you will love it!! And the cranking is not that bad, but be aware that sometimes. . . . . ever' now and then. . . . .:( :(
My buddy was trying to moto on a completely stock KDX and the stock KDX suspension was hopeless on the MX track. The YZ is in a whole 'nother league!! Power, suspension, brakes, noise; the YZ has it all!!
Apples and oranges!!
If you can crank it you will love it!! And the cranking is not that bad, but be aware that sometimes. . . . . ever' now and then. . . . .:( :(
Big CR man
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- May 17, 2001
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Try it
Crusty took the words out of my mouth . I would try the blue wire mod . It gave me hope again . By the sound of it its starting to work for more and more people . My bike fouled plugs almost every time . Now it doesnt ( HMMM- must be something to this mod ) I would definately try it. It costs nothing and its extremely easy to do and If if it doesnt work . Put the wire back on . I live in the land of now storms and cold weather and my bike staarts perfectly every time . I ride year round ( In the winter I studd up and ride the river ) . This is my own opinion , but its something I'm glad I did .... TRY IT
Crusty took the words out of my mouth . I would try the blue wire mod . It gave me hope again . By the sound of it its starting to work for more and more people . My bike fouled plugs almost every time . Now it doesnt ( HMMM- must be something to this mod ) I would definately try it. It costs nothing and its extremely easy to do and If if it doesnt work . Put the wire back on . I live in the land of now storms and cold weather and my bike staarts perfectly every time . I ride year round ( In the winter I studd up and ride the river ) . This is my own opinion , but its something I'm glad I did .... TRY IT
PowerStroke
Member
- Dec 3, 1999
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Double check all connections.
Check the spark plug boot. I have had 3 out of 3 yamaha (wr250(2) yz80 all 2-strokes) go bad. This leads to a plugs always fouling. Even with jetting a little off the 4 strokers can usually keep the plugs alive.
Also a bad batch of fuel maybe from last season can kill plugs. Get some new fuel.
Also take off the plug boot and make sure it is screwed into the copper real good.
Good luck.JR
Check the spark plug boot. I have had 3 out of 3 yamaha (wr250(2) yz80 all 2-strokes) go bad. This leads to a plugs always fouling. Even with jetting a little off the 4 strokers can usually keep the plugs alive.
Also a bad batch of fuel maybe from last season can kill plugs. Get some new fuel.
Also take off the plug boot and make sure it is screwed into the copper real good.
Good luck.JR
