Keep fouling plugs

[Brett]

Please help.
I went for  a ride few weeks ago and bike decided to foul plug while riding along track in fifth half throttle.  Managed to get it home (very scary as went road way and had to give it full throttle which would make it die and then randomly go full noise lifting front wheel)  I at first thought i had a blocked low speed jet but when i checked it was fine.  I checked reed petals they fine. 
What happens now i put a clean plug in start it ride 200m and it doesn't like any throttle and then it floods up.  I push it back (cursing) remove plug, wack another in and same thing.
I have chunks missing from shin due to slipping off kicker on numerous occasions and am right p***ed off.
What could it be cr**py ignition?  I did the old put the finger on plug while kicking and yes it really hurts.
I dropped the needle with no effect.
Thinking bout trying a ngk 7 plug and also leaning all jets back (although has been running great up untill now)
Its moments like these i wish i bought a 250.
Could someone give me a few ideas of what it could be and also what are the specs to check the coil and do rotor's demagnatise after a while?   Its a 91 model

[Paul]

What plug are you using?

[Brett]

I have been using a B8EGV but just then i tried a B7ES (cheapest cr*piest) and it did last longer but i cannot give it more than half throttle without spluttering.
I've checked the carby and nothing stuck in it and i refuse to believe the weather could just suddenly run piss poor.
Therefore im leaning to ignition so i need to know specs to check it.

[hughes]

Float height? Have you checked it? Did bike run great until now?

[alan]

Hughes is right, you have some other problems! The fowling plug is a just a symptom of the real problem. When did the problem start?
When I first got my KX5 I use to fowl plugs all the time and I think it was mostly my riding technique. I was bogging it down to much and also I was running to rich of oil mixture. What fixed my fowling problem was, I put a reed spacer on and an FMF Gnarly pipe, which vastly improved the mid range power. I found I could run one gear taller without fowling plugs. Also I think a 7 plug is to hot and you will end up wit some other problems. I run 8 & 9's mostly Iridium and Platinum's and I find they are much better for my style of riding.

If this isn't a new problem you really need to look at jetting and oil mixture. I am sure you will got lots more hints from the other members!

Alan

[5dracing]

One other thing to think about is the quality of the gas.  How old is it? I have a mechanic that just got back from a small engine repair training and they stated that gasoline is only maintaining its octane rating for about 2-3 weeks.

[Brett]

Previously the bike hauled arse, so something has definately happened and is not just jetting.  I will rip the carby off and double check for something obvious like float split and full of fuel and i'll rip the magneto off to see if it has slipped a bit.
Other than that i do not know how or what the specs are for resistance in coil to see if that isn't weak.

[Spider]

Before I went to all that trouble I'd go with a fresh batch of fuel paying attention to the mix ratio. I put oil in the can then went to the station and put oil in with the gas. What a smoking mess. I couldn't figure out what was wrong until my buddy asked what happened to all the oil we had.

[Brett]

Na its not the fuel cos i checked fuel flow from tank and drained that and mixed up a fresh batch.
Today i figured out that if i didn't give it throttle i could ride it happily (1/3 throttle) but if any more it would misfire.  Then i stopped riding and in neutral if i slowly increased rpm it would splutter at 1/3 throttle and die if any more.  I tried 2 other coils and it still splutters when increasing throttle slowly.
I reckon it must be black box or pickup coil half stuffed what do youze reckon??

[gowen]

Post up a picture of the plug, I can easily diagnose a plug. But, from what you are saying. Any smoke when more than 1/3 throttle? I have a hard time considering a CDI because usally it does not foul the plug. Just runs like crap. I doubt the ignition because it would not start easily or at all. But I could be wrong. Give a plug condition. They do not foul for no reason. Check your ignition position. It might have moved.

[alan]

I would like to hear what doordie thinks about this problem! I wonder if it could be a reed problem? otherwise I would have to go for the CDI?

[gowen]

NOw that I think about it, I had a friend that had a little CR80R and was having similer issues. It turned out to be a bent needle jet. Check the condition of your carb's needles/jets.

Remeber your powervalves, they might be stuck causing excessive issues?

KXCam is the man when it comes to these issues. But if it were my bike and the reeds looked fine, I'd start with the obvious. Clean the carb completely. Try leaning the entire circut to see it it helps, then go to compression, then ignition and so on.

[KXcam22]

Brett,
  It sounds to me like something has changed (failed) on your bike.  It would be best not to change jetting or plug heat range - might give you a real surprise later.  It is something else. There are a few possibilities to check:

1. I doubt it is the CDI. generally those will cause excessive kickback on starting or low speed mystery seizures.  It will not however change your jetting to rich.

2. Cracked/leaking float is possible but you will see lots of unusual overflow from the carb.  Also good to check the seat and the needle as leakeage will cause runability problems, but not as super rich as you describe.

3. Cracked reeds: Will make it run like crap but not change jetting to rich.

4. Leaking oil crank seal.  Will foul plugs oily black. Bike will run OK but smoke a bit/lot more.

5.  Here is what I think it is.  Something is wrong with the jet needle in carb.  Check the mounting of the needle in the slide.  If the needle is not retained (broken clip) it can slide up and make the mid throttle mixture super rich - liker raising your needle a 1/2". Guaranteed to foul plugs.  That would create your symptom of running fine (full throttle) on the main jet but dying when you close the throttle to 1/2 -3/4 range (super rich).  Bike will also start OK (other than the mostly fouled plug) but start to die as you open the throttle. 

Hope this helps.  When you find the prob let me know so it will be one more for the memory banks. Cam.

[alan]

Thanks Cam! Great INFO! It did sound like cracked reeds to me!

Alan

[KXcam22]

Alan,
  You still might be right. Enough of a broken reed and the mixture gets sucked back and forth, in and out of the carb and gets progressively richer, the ole "loading up" of the old days pre-reed valve bikes. I forgot about that. Cam.