1998 YZ250 frying plugs.

[diesel_dean1]

My YZ has been having an issue for quite awhile frying plugs, not fouling them just burning them so they don't conduct anymore. but what caused it to kick off is I pulled the head and cylinder off to check the cylinder, piston, rings, etc. and everything is practically brand new. running around high 180 cold, no play in the crank, no leaking crank seals, gaskets etc. But what stumps me is how it fries plugs. It has gotten better and ive achived more life out of my plugs since i sanded my engine mounts, the part of the head where it holds the bolt for the bottom part of the engine mount and on the frame. I replaced my cdi thinking it was over charging the plug, i tested all of my wires my stator, coil, and anything that really can be tested and it seemed to be in the correct ohm range. Although, a previous owner had a shop replace the stator so its practically brand new, i replaced the CDI, plug boot, obviously plugs but not my coil. Could a bad coil be causing it to over charge? Today i went riding with a buddy of mine and we rode for a solid 4 hours and lots of wide open riding as well as lots of through the woods putting around in the woods, so there was lots of different riding conditions involved, and then I was riding wide open and the bike died like I hit the kill switch. it does it the same way every time it ruins a plug, like i hit the kill switch. swapped the plug and fired up first kick. It aint a jetting problem because i have power everywhere and i had full power whem the plug quit out of no where. This has been going on for a year or so now, some last longer than others regardless on riding style or area, but what do you guys think, an over powering coil? or is it just cursed... With a fresh plug up until it dies will start first kick cold even after weeks of sitting but once that plug quits its done.

[Thermos O Flask]

My mate and I both have '98 wr250's same as YZ with the PWM carby. We both killed plugs when we changed the pilot jet from stock 48 to 45.
Even though we live at sea level and ride at 3,000ft . Bikes are lovely with 45pj but just kills plugs put the 48 back in and off she runs. I think also its the crappy yamaha needle I have a suzuki NEDW in it now with the 48 and its so smooth.

[diesel_dean1]

My mate and I both have '98 wr250's same as YZ with the PWM carby. We both killed plugs when we changed the pilot jet from stock 48 to 45.
Even though we live at sea level and ride at 3,000ft . Bikes are lovely with 45pj but just kills plugs put the 48 back in and off she runs. I think also its the crappy yamaha needle I have a suzuki NEDW in it now with the 48 and its so smooth.

It isn't a jetting problem, because it could either die wide open throttle or at a low rpm, it goes whenever it wants really

[Thermos O Flask]

Are you using resisted plugs?

[diesel_dean1]

Are you using resisted plugs?

BR8EG, stock plugs unless some &%$#@!ass put a high output stator on it

[scotearl]

I have what seems to be a very similar issue with my 2005 yz295. I've been chasing what seemed like carb issues for a while which culminated in no spark. The plugs looked almost like new, but wouldn't produce spark. I finally plugged a brand new one into the coil and kicked it through and it wouldn't show signs of life.

Feeling I had an issue with the stator/coil/cdi, I took it over to my buddies garage for an afternoon of wrenching. Before we started taking things apart, we ran through the "check for spark" drill one more and saw nothing.

Just for yucks and grins, Kenny grabbed an old plug off of his workbench and we tried it - and got a huge spark! We buttoned everything back up and she fired up right away. Yay!

Here's why I'm posting this: the plugs my bike was killing were all BR8EG's, while the old, tired plug that worked great was a BR8ES. Go figure.

So, I'm suggesting you try an S plug and see if that helps your situation as much as mine.

Also, I'd be interested to know if any of you out there have comments or thoughts as to whether or not going from a G to S switch would improve spark.

[diesel_dean1]

I have what seems to be a very similar issue with my 2005 yz295. I've been chasing what seemed like carb issues for a while which culminated in no spark. The plugs looked almost like new, but wouldn't produce spark. I finally plugged a brand new one into the coil and kicked it through and it wouldn't show signs of life.

Feeling I had an issue with the stator/coil/cdi, I took it over to my buddies garage for an afternoon of wrenching. Before we started taking things apart, we ran through the "check for spark" drill one more and saw nothing.

Just for yucks and grins, Kenny grabbed an old plug off of his workbench and we tried it - and got a huge spark! We buttoned everything back up and she fired up right away. Yay!

Here's why I'm posting this: the plugs my bike was killing were all BR8EG's, while the old, tired plug that worked great was a BR8ES. Go figure.

So, I'm suggesting you try an S plug and see if that helps your situation as much as mine.

Also, I'd be interested to know if any of you out there have comments or thoughts as to whether or not going from a G to S switch would improve spark.

The time that I did run a br8es was before i pulled the motor apart so that does make sense, the G plug is a "racing" plug which uses a fine nickel wire i'm nearly certain and the S is a standard 2.5mm electrode. And if the G is racing as it claims, it probably isnt designed to run for longevity and should be changed every race or so. But thank you I will definatley try that

[scotearl]

Well, after riding around for thirty minutes yesterday with no issues, it ate the BR8ES today. 

Started on third kick today with the S in it.  While it was idling and warming up, I cut the choke and it soon died.  Wouldn't restart.  Sounded like the plug fouled, so we put a new plug in.  This time is was a Iridium BR7IX.  She started right up and life seemed to be good again.  After an hour or so of hard riding, it sputtered and died.  I took the IX out to look at it and it really didn't look that bad.  Some carbon had built up on it, but not what you would expect to foul it.

I dug around and found a brand new BR8EG in my gear bag, so I plugged it into the cap to see if we had spark - no.  So, I suppose something in the stator/CDI/coil chain is failing when it gets hot.  I'd have to go further to postulate that this failure is also deadly to spark plugs.  We tried the failed S and the IX in my friend's KX250 and they were truly dead.  The new G did show spark on his KX (but it was very faint/weak).

My next step will be to try the new plug again when the bike has completely cooled off.  If it sparks, that should confirm that it's heat related. 

[diesel_dean1]

Well, after riding around for thirty minutes yesterday with no issues, it ate the BR8ES today. 
Started on third kick today with the S in it.  While it was idling and warming up, I cut the choke and it soon died.  Wouldn't restart.  Sounded like the plug fouled, so we put a new plug in.  This time is was a Iridium BR7IX.  She started right up and life seemed to be good again.  After an hour or so of hard riding, it sputtered and died.  I took the IX out to look at it and it really didn't look that bad.  Some carbon had built up on it, but not what you would expect to foul it.
I dug around and found a brand new BR8EG in my gear bag, so I plugged it into the cap to see if we had spark - no.  So, I suppose something in the stator/CDI/coil chain is failing when it gets hot.  I'd have to go further to postulate that this failure is also deadly to spark plugs.  We tried the failed S and the IX in my friend's KX250 and they were truly dead.  The new G did show spark on his KX (but it was very faint/weak).
My next step will be to try the new plug again when the bike has completely cooled off.  If it sparks, that should confirm that it's heat related. 

My thing is i can be riding wide opem for 2 hours and it will not die out, so it isnt heat related. I'm thinking im over charging with a bad coil. I have a new stator and cdi box. my plugs die whenever they feel like it. and right after it dies i can swap a brand new one in it amd it will start first kick