250-500cc Spark plug issues

Hello fellow husky riders/owners,
I am having trouble with my 2009 WR250. It is going through spark plugs at phenominal rate. The plugs appear to be burning out in the core as the tip is still in good condition. If I rev the bike hard they fail even faster. I am talking every 15 to 20k's and faster if I rev it hard. This is what i have done/checked so far before everybody tells me to do it all again. It runs fine for a while when a new plug is installed but then it too starts to break down and fail.
Rewind on Stator
New ignition coil fitted
have checked all earths....all good
Jetting is very good
Float level is good
I have had the bike since new and it ran for 4 years without a problem. Now my frustration level has come to an end. any help would be much appreciated.

Not sure why this went straight to 125-200cc heading.

This is a plug after about 35 minutes and failure. Yes it is black as it runs rich just before it splutters to a halt

I have tried the iridium spark plugs, but alas they fail just as fast as the cheap ones. Once they fail, they are as dead as a duck. No spark at all. I will try the core resistance test and see what that shows. Thanks for that. I am thinking maybe spark plug cap replacement after reading some other forums about plug cap failures and symptoms. They seem pretty similar. I guess I have to try something.

Have you changed oils by any chance? I have known certain types of 2T oils to kill plugs in a matter of a ride. Find some fully synthetic oil and see if it lasts longer maybe.

A B9 is a pretty cold plug. I cant tell from the picture since the part of the plug that tells you the most about what is happening is up inside on the porcelain. From what I can see it is fuel fouled. The most common causes of fuel fouling are, too rich, bad fuel, too cold of a heat range plug or a weak spark.

Ok, I have tried B9 down to B7 and yes the expensive iridiums as well. It looks rich as i have to short shift and not rev it to try and make the thing last for at least a little while. I have not changed the jetting from when it was running good. I have tried synthetic oil and mineral oil as well. Different types of oil don't seem to make much difference nor do different grades of petrol. 98 down to 91 octane. So it is not fuel related. I know it is electrical of some type but I am out of ideas. I am just wondering if anybody else has had this or heard of similar problem.

It can still be a fuel problem. For example, just because you set the float level doesn't mean that your needle and seat is sealing off. If the needle is not holding the float level will rise while the engine is vibrating and you're hitting bumps. This will drown out plugs about as fast as you can screw them in. The needle can get a ring worn on the sealing area and leak by. Some Mikuni carbs have an "O" ring around the brass seat that will go bad and leak by essentially bypass the needle causing a rich condition. Although it's rare I have heard of a couple carbs that got wallowed out where the needle goes through the main well of the carb causing a rich condition no matter the jetting.

This happened to a friend of a friend who had a GasGas, the subject came up when the guy was bragging about how reliable his GasGas was in that the carb wore out before he did his first top end. (this guy rode tons of hours and miles in the woods for about 6 years with no maintenance)

Some more info might help like;

When you rev the bike holding the throttle wide open does it cut out immediately like you're hitting the kill switch or does it run rich until the plug fouls?

Have you tried disconnecting the kill switch to eliminate the possibility that it's faulty?

What is your current jetting?

Have you cleaned the carb to make sure that all passages are not obstructed? For example the pilot circuit mixes air with the fuel but if the air passage is blocked it will run very rich.

I'm not sure what year the WR250 was but a couple of years ago someone posted on here that they had a voltage regulator go bad which caused some ignition problems. I was thinking it was a newer WR like 2010 or 2011 with the digital ignition. The 2009 has the older ignition which was stone reliable, in fact I can't remember anyone with the older ignition having any stator or ignition faults unless they were caused by another problem. (like a kill switch)

Before I bought a Lectron carb I had my 2009 WR250 mikuni working about as good as one can work and I'd be happy to sell it cheap ($100 with an extra needle and some jets) but I noticed you were from Aussie land so shipping would hinder that and it probably wouldn't suit you anyway since I understand that Aussie fuel is much different then what we get in the US.

when you ride it hard is the plug clean
try this, put a new plug in it and push it for about 10 minutes and pull the plug
take a good close up and see what the color is, while it still runs strong

If not electrical it could be a leaking crank seal on the clutch side sucking in small amounts of transmission fluid. Try BR8ES plugs once sorted out (even tho you've tried 7-9 range). They're cheap and work great.

How much smoke is there at high rpm or right before failure? Looks oil fouled to me.

was working great for long in hours with all the same settings and now its fouling, usually indicative of a crank seal (on the wet/trans oil side). can be other stuff as well and even low compression. But these bikes are tough, long in hours, I'd check the crank seal(seals)

As stated i was going to suggest crank seal, are you going through gear oil?
Does the gear oil smell of fuel? If so its crank seal, had this on my 360 after i rebuilt bottom end i buggered up installing the seal square, it lasted about 5hours before it fouled a plug then it was every time i reved it longer than three seconds.

Carbs do wear out and jetting requirements do change but i suspect seals behind this issue.

I suspect the main jet is too rich. I had similar problems a few years back when I went from a 2008 wr250 to a 2009 wr300 and put my Keihin from the 250 on the 300. After several months of fouling plugs just like you described (at higher revs) I went back to jetting basics and ended up going from a #175 main which always worked perfect in the 250 to a #162 in the 300. That's 5 sizes smaller, a huge difference.
Go down one main jet size at a time and take plug readings. The plug should not be black with black oil stains all the way up the threads of the plug. The proper plug is a B8ES.

As a point of interest, I have totally given up jetting carbs. I have now been running an APT SmartCarb all year and have been getting proper plug readings. And after a simple initial set up I have not touched it. I even swap it back and forth between my 2009 WR300 and my 1986 430AE auto with absolutely no jetting adjustments. Fuel economy was improved by at least 20%, I can now go over 3 hours at race pace in a hare scrambles with a 9.5 litre tank on the 300 or the 430. I have been tracking fuel economy at every race I have entered since 2007. I was using anywhere from 3.5 to 4.5 litres per hour with the Mikuni and Keihin and now with the SmartCarb I have never used more than 3.0 l/hr. This is in no way a sales pitch, just my documented results.

Best of luck finding a solution, I think jetting is where to start looking.

I had a similar issue on my 125, I changed every electrical item on the bike, changed pre-mix and the crank seals.

It ended up being low compression, changed the ring and stopped having issues. I think leaning out the jetting would have acomplished the same thing. I was fixated on electrical and was sure it couldn't be jetting.

This is what my plugs looked like...


Later,