Rode yesterday, no Plug Fouling, but running rough! Help?


Someone has mention about some bad GAS in the area? (No pun intended)

Drain all your fuel from the tank, also install new inline fule filter.

Good Luck

Keeping the fuel filter is a good idea. Pingel makes a high-flow petcock valve that will supply the carb with plenty of fuel so the filter will not be restrictive enough to cause a problem. I had the same concerns about adding filter so installing the Pingel was my alternative that has worked very well. It's amazing the amount of junk that gets in the gas tank. I even resorted to filtering my fuel through a coffee filter as I poured it into the tank. As an additional tip, a little water in the tank will cause these symptoms. Water will collect on top of the petcock screen and will restrict the flow of fuel. It happened to me about a year ago and drove me nuts until I shined a strong flashlight into the tank and could actually see the water sitting on the screen. It looked like a white marble. I picked up a long pipette from work and sucked it right out. Cured that problem. Sometimes, it's just a little thing.

[ May 20, 2002: Message edited by: Boit ]


I'm still betting on the plug. I have lots of experience. If your plug is partially fouled, it may be harder to start but not necessarily. It will idle fine, as good as with a good plug. If you have an open pipe, it will sound harsher and slightly higher pitched than normal. As you build RPMs, it will crackle. Lean pops are muted, these are much sharper, crisper crackles. As RPMs go up, you may get loud backfires, it will bog and cut out. When you let off, when it gets down within 1K of idle RPMs, you will occasionally get wet sounding flames (not the boom sound of a big backfire, more of a gob of gas burning rapidly in exhaust).

If these sound like your symptom, replace the plug.

Good luck,


p.s., if it is the plug, I will be glad to discuss how to avoid.

Well the debate continues, The problem here is that I have not had any of these problems with the bike till now. I have not fouled a plug yet since these problems have occured. The only time I fouled any plugs was when I overoiled the filter or somebody twisted the throttle when I had a party. I will replace the plug again but when these problems started occuring I did replace it and as soon as the motor is started it will bog if you punch the throttle at idle, or crackle and pop resulting in a loss of power on certain sections of my track. What about a CR7e (hotter plug right?), Needless to say something is wrong! Whether it be carberated prob's or plug? I dam sure hope it ain't electrical. What about going to a 45 or 48 pilot? Moving the needle, after cleaning the carb completely.....Just let me know? I will probably pull the carb tonight and clean it completely. And I have a CR7E that I could throw in there, last time I had that plug in there it ran great, just don't want the plug to damage the piston if the "7" might be too hot? I just want the bike to run like it did! Thanks for all the suggestions and any more are welcome!!Frank :)

I debug things all day long and the one thing that I can suggest is that you first set it up identically to how it ran good in the past. For example, if it ran great stock then put everything stock before you change anything (even the spark plug). If it runs poorly then it will be easier to figure out what's wrong because you've already eliminated a number of items from the list of potential problems.

If you start mixing your known good settings with "I'll try this" type settings then it can be very difficult to figure out where the actual problem is. Hope this helps. :)

thanks thumpalot, I will be doing that if I can't get it to run right after I clean the carb. Only thing is that it did run good after the bkmod, and I really have not changed much since then other than the air filter. Who knows I can't ride this weekend so I got a little time to diagnose some more. I will get it right eventually. Thanks for all your help guys!! Frank


If the noise is a crackle, sharper sounding than the pops you get on deceleration, the problem is not in the carb. The problem is electrical. Either you plug is partially fouled or you have some other electrical problem. A loose plug wire. A bad coil. A bad CDI. A bad stator. I know I'm going to lose a lot of face if it is jetting, but I'm pretty well convinced.

Good luck,


Well let's hope that it is not electrical. I pulled the carb off last night completely. Must say that it was easier than I thought it was going to be. I pulled the carb completely apart and cleaned throughly with carb cleaner. Now I might catch hell for this but I altered the jetting again. I moved the main to 168, the pilot to 45, and the clip to the 5th position from the top of the needle. I put it all back together but I did not have a new plug to put back in. So I tried to clean the 3 plugs that I had w/ carb cleaner and sandpaper but I think I ended up fouling all of them out. The bike would start firing for about 1 second but that is all I could get out of it after ruining a pair of shoes I had on after kicking about 30x. I will get a plug today and then try it out tonight. If it will not start with a new plug then I am going back to completely stock and going from there. I am pretty sure the plug is why it won't start, but after it is running we will see how the carb set up works tonight on the track. wish me luck!! Frank

FASTFRANK, Please let me know what you find with your bike because I am having the same problem! I have a stock 01' YZ426 and after changing the filter one day it started running just the way you described. After reading the posts on this thread, I cleaned and installed a lightly oiled filter, fresh gas, new plug, cleaned all jets and blew out carb with cleaner and air. No change. Seems rich, plug is always black and sooty. Even the exhaust tip has a sooty residue in it. I checked my valves about 2 rides ago and they were in spec but on the tight end. This is very frustrating as the bike always ran great and all of a sudden started running crappy. I didn't change anything. HELP!!!

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