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02 YZF Fouling plugs and backfiring

Joined
Oct 1, 2001
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#1
Does any one have any suggestions as to what might be causing my 426 to foul plugs on a regular basis? Last year it ran great and never fouled a plug this year I have fouled about 10 plugs. I've changed the brand of gas I'm running but this has not helped. Also I've noticed that the bike wants to back fire and miss on occasion. I think it is a carb problem but I am open to any sugestions.
 

Weld it

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Joined
Feb 19, 2001
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#2
Did you check the TPS ( throttle position sensor ) on the carb ? I have seen those go bad and give the same symptoms, to check it get you owners manual out and it tells you how to check to see if it has gone bad.
It's a electrical part and spendy at that .......... :eek:


Weld it
 

EdLennon

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May 10, 2000
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#5
I read somewhere that a popping or backfire could be caused by an exhaust leak, perhaps at the cylinder/head pipe or where the headpipe enters the silencer.

Did you perhaps remove the pipe recently? Maybe it's not back 100% the way it was. Just guessing.

If not, it's probably a carb problem. I had the same problem (popping) a month or so ago. I took the carb apart and cleaned and blew out all the jets. Seems to run just fine now.

HTH,
Ed Lennon
 
Joined
Jun 3, 2002
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#6
My WR had the same symptoms. It was the screw inside the spark plug boot. Take the boot off the plug and shine a flash light in it. Take a flat screw driver and check if it is tight. Use the flash light to see how the screw is turned, then try to turn ~1/4 of a turn and recheck to see if has turned(Just to make sure the flat head isn't too big and won't fit the screw). This happened to me last year. Every time I changed a foul plug I actually kept loosening the screw more and more because I had to turn the boot slightly to get it off. Good Luck!
 
Joined
Nov 4, 2003
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#8
Do the blue wire mod on motoman393.thumpertalk.com click on tech articles, then how to make your YZF start better. I had the same problems and never fouled a plug after the mod
 

EdLennon

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May 10, 2000
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#9
Wow! That worked wonders for me. I hated starting my bike. It took forever. I disconnected that little baby blue wire and my bike starts first kick every time. I stalled it 3 times in the yard just to start it again.

I do think it's wierd though that once it's warm, I can only start my bike with BOTH the choke out and the hot start button out. Do you think that something needs to be adjusted in the carb?

Thanks again for the tip!

Ed
 

Thump

Jr Admin Type
Joined
Jan 17, 2000
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#10
If it is fouling a plug the first time out after washing it you may want to start putting a golf T in the small hole on the right side of the cylinder. It is a drain hole to drain water away from the plug i believe but you can push water up in there when you wash it. Then most of us fire the bike up to dry it and shut it down. Then the next time we kick it over it sputters and fouls a plug. Why I don't know but the golf T works like a charm on the 250F and on my old 426's.