Age old question

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#1
I've been riding my 2003 YZ 250 the since late April. Im mix 40-1 and lately I've fouled three plugs. The first plug I took out this spring had been in the bike for a long time. I do alot of woods riding and Im wondering if this is the cause for the fouling. I can ride all day hard and not have a problem, but next time I take the bike out I foul a plug . Im using klotz oil and a br8es plug. Im wondering if I accidently mixed it a little to rich with the last 5 gallons of gas. I love my two strokes, but this just gets old after awhile. :(
 
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#2
It's probably a jetting prob. Riding woods as you know you can't stay in the rpm's thus the engine relies on the lower end jet's, like the slow jet, it controls from idle to half throttle or a little more as well as the needle jet, lowering the needle jet with lean it on the bottom side of the throttle. At half throttle all have a roll, but if your not in the band, the slow jet is the main player. Dropping a size for example going from a 45 to a 43 will lean the bottom. I use a BR7es, it's hotter than the BR8es. On my KX250 I'm currently running a 45 slow jet, a 158 main and the needle is in the 2nd notch from the top, the bottom is still a little rich but just haven't gotten around to picking up a smaller slow jet. Oddly enough as it may sound mixing your gas with more oil will lean it and taking away will make it run rich.
 

_JOE_

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#3
GoT_GreeN said:
It's probably a jetting prob. Riding woods as you know you can't stay in the rpm's thus the engine relies on the lower end jet's, like the slow jet, it controls from idle to half throttle or a little more as well as the needle jet, lowering the needle jet with lean it on the bottom side of the throttle. At half throttle all have a roll, but if your not in the band, the slow jet is the main player. Dropping a size for example going from a 45 to a 43 will lean the bottom. I use a BR7es, it's hotter than the BR8es. On my KX250 I'm currently running a 45 slow jet, a 158 main and the needle is in the 2nd notch from the top, the bottom is still a little rich but just haven't gotten around to picking up a smaller slow jet. Oddly enough as it may sound mixing your gas with more oil will lean it and taking away will make it run rich.
SOME of this is correct.
 
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#5
YZ/250 said:
I've been riding my 2003 YZ 250 the since late April. Im mix 40-1 and lately I've fouled three plugs. The first plug I took out this spring had been in the bike for a long time. I do alot of woods riding and Im wondering if this is the cause for the fouling. I can ride all day hard and not have a problem, but next time I take the bike out I foul a plug . Im using klotz oil and a br8es plug. Im wondering if I accidently mixed it a little to rich with the last 5 gallons of gas. I love my two strokes, but this just gets old after awhile. :(
When I trail ride my YZ250, I run a BR7ES instead of a BR8ES or BR8EG. What you described was a cold foul. When trail riding the plug isn't getting up to normal "self cleaning" temp and gets a coating of carbon. Not enough to fould then but at the next start before the plug can get warm it loads up about 30 seconds or so after you start.

To jet it lean enough to prevent it would likely require going too lean.

Running a BR7ES when trail riding is perfectly fine and won't hurt anything.
 

_JOE_

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#6
Sorry, I didnt have time. The pilot/slow jet controls low throttle operation(closed to 1/8th)along with the air screw. These jets along with the slide type effect 1/8th to 1/4. The slide and needle control 1/4 to half throttle operation. The needle, main, spray bar and air jet control 1/2 to full throttle. The slow jet is not important at half throttle as needle and main have taken over. And since gotgreen doesnt know where he lives and rides a completely different machine his jetting is of no relevence to yz/250. How old is the top end? Are the reeds in good shape. Do a search for plug chop. This is the only way to accurately check the main circuit. There is a wealth of info from people who know what they are doing. Buy Eric's book, too. It is very informative. Sorry so short in the first post. Good luck yz/250. :cool:
 
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#7
YZ,your bike has a little more than a main,pilot and needle controlling your carb!It has a power jet or ap circuit,fuel shut off sensor and throttle position sensor!You should not go THROWING hotter,incorrect plugs like darts at your bike!If the STOCK temperature plug SAYS it needs to be hotter,then put a hotter plug!Dropping one or two heat ranges to compensate for jetting and or mechanical reasons is silly!And worse is it does work to a degree!Jetted properly you should have no issues,except for special applications,like desert racing,it would require a richer carb!The BR8EG is an inexpensive plug,racing applications I would put the BR8EIX in.
 
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#8
whenfoxforks-ruled said:
You should not go THROWING hotter,incorrect plugs like darts at your bike!If the STOCK temperature plug SAYS it needs to be hotter,then put a hotter plug!Dropping one or two heat ranges to compensate for jetting and or mechanical reasons is silly!And worse is it does work to a degree!Jetted properly you should have no issues,except for special applications,like desert racing,it would require a richer carb!The BR8EG is an inexpensive plug,racing applications I would put the BR8EIX in.
Not sure if you aimed that at me; but your bike can be jetted right and still need a hotter plug you know. The standard plug heat range as listed by the manufacturer is targeted for the intended use the manufacturer designed it for (MX in the YZ's case). Deviate from that one way or another enough and a different plug heat range can be called for.

Trail and woods riding generally involves a lot more low/closed throttle so there isn't as much heat being generated to keep the plug at its optimal "self clean" temp and it developes a carbon coating. One step hotter plug will help burn these deposits off preventing the cold fouling symptoms he describes which generally happen at the next start-up.

You are correct changing heat ranges to fix bad jetting is not a correct approach and also to never jump two ranges hotter; but just as well trying to get your bike to run lean enough (hot enough) to get a too cold a plug for the use the bike is seeing can be wrong as well.

If he was fouling while riding I would look to jetting as the main cause; but his description of it running fine all day and fouling at the next startup the next day points to too cold a plug for the type riding being done.
 

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#9
I agree with foxforks, I would try leaning the low speed circuits first. That is if the engine is fresh.
 
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#10
I know I have good compression. I checked that last winter. At least I had it then... I've had both plugs in the bike(br8es and eg). I was told the the br8eg was a hotter plug than the es. Im about ready to pull the carb off and check the jetting. I'll look at the reeds while i have the carb off. I had a 91 that would foul plugs and that ended up being crankshaft seals. That is NOT what i want to deal with on this bike.
I was doing a lot of slow riding the other day and Im sure thats what killed the plug. I probably had 2-3hrs on it before I fouled the plug. Maybe i just need to ride with the throttle wide open! :nod:
On my older 91 YZ I rebuilt the carb, dropped the needle, put in new reeds, new air filter, and I still didn't win :bang: Im sure that it was crankseals on the older bike. I sure hope thats not the problem with this bike. Funny thing is that i went riding for several sundays this spring before i even had a problem with the plugs. :think:
 
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#11
YZ/250 said:
I've had both plugs in the bike(br8es and eg). I was told the the br8eg was a hotter plug than the es.
No. Technically they are the same heat range. The ES is the standard (thicker) center electrode while the EG is the thinner fine wire electrode. According to NGK the EG should resist fouling better than the ES. While this may be true during running condintions, I feel the EG is more prone to the cold fouling than the ES.
 
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#12
I have an 04 yz250 and have the same exact problem as your describing when its not ridden to hard. Ive changed the crank seals, checked reeds, checked the top end, leaned out the jetting and mixed the gas 40:1 instead of 32:1 and I havent solved this problem yet. The only way ive managed to reuse an old plug after a day of woods riding is to hold it wide open on a straight where i can get threw all 5 gears just before putting it away. If i dont do that the plug fouls on start up within a few seconds. Ive used the br8eg and br8es and a br9eix (took the eix from my brothers bike after i run outta plugs) and they all do the same thing. Im also using amsoil dominator pre-mix oil and since i noticed this problem ive used klotz r-50 and a few other oils and nothing changed. Right now im out of ideas about what will fix this problem.
 
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#13
Just to add my 2 cents :)

My bike was bought from a former MX racer. It was completely setup for MX racing, including jetting.


This past weekend I took this exact bike to a 60 mile enduro. I spent 80% of the time in 1st gear crawling along. I didn't change the plug before the start of the race nor did I change it after.

Last night I took the same bike to the local track, same plug since I bought it. Ran fine.


The changing of plugs to fix jetting issues is somewhat of a bandaid fix. There are situations where I would temporarily move colder or hotter, but that would be a quick short term fix (aka new person learning on my bike, taking my bike out on a sandy track on a 100degree day, etc)


As foxforks said, unless you are using this engine for some type of extremely odd situations (dessert racing), the stock plug (and proper jetting) will work fine.


Now you might have something else wrong with your bike, such as a seal leaking oil into the cylinder. You best bet is to attempt to jet the bike.
 
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#14
mox69 said:
Just to add my 2 cents :)

My bike was bought from a former MX racer. It was completely setup for MX racing, including jetting.


This past weekend I took this exact bike to a 60 mile enduro. I spent 80% of the time in 1st gear crawling along. I didn't change the plug before the start of the race nor did I change it after.

Last night I took the same bike to the local track, same plug since I bought it. Ran fine.


The changing of plugs to fix jetting issues is somewhat of a bandaid fix. There are situations where I would temporarily move colder or hotter, but that would be a quick short term fix (aka new person learning on my bike, taking my bike out on a sandy track on a 100degree day, etc)


As foxforks said, unless you are using this engine for some type of extremely odd situations (dessert racing), the stock plug (and proper jetting) will work fine.


Now you might have something else wrong with your bike, such as a seal leaking oil into the cylinder. You best bet is to attempt to jet the bike.
What jets do you have in it vs stock? Each bike/brand is different so blanket statements don't always hold up.

I just find it almost funny that I see people screwing with jetting to the point their bikes run worse; but treat plug heat ranges like its some set in stone standard never to be touched.

Just like jetting, its another tool at the tuners disposal. And like indiscriminant changes in jetting shouldn't be made, indiscriminant changes in plug heat ranges shouldn't be made either.

Try it for a ride; pull the plug and have a look. If it helps great; if not go back to the standard.
 
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#15
This has been covered,many times before!There is at least 6 threads that should go to the frigging smithsonian institute!All you have to do is search,ooooooh wait a minute,allow me :http://dirtrider.net/forums3/showthread.php?t=48348 http://dirtrider.net/forums3/showthread.php?t=92818 That was not that hard.Myself and many others have gone threw EXACTLY your situations,special you may be but the real answer you are looking for is in your head(or about to be).Sad fact is I can not give you your jetting for your bike,it don't work like that as you may learn.I have read these posts and you would not believe some of the other information available!Good luck and get reading!