I have a '03 400ex. Its got K-n-N filter and white brothers exhaust.Ran well for a few weeks and now it seems to foul the plug.The plug is black and dry.Do I need a hotter plug due to the mods? But it seems that it would run hotter due to better air flow both in and out.Please help if you can.

 

What is your jetting like?

 

The Jetting is stock.

 

I think you are in trouble! Stock jetting will be way LEAN with a K&N and pipe. Stock factory jetting is lean already (for emissions) to start with! Your engine may be badly damaged (although a lean plug should be gray). In fact, I am surprised the thing ever ran well with stock jetting.

 

It has ran fine,just have troulbe starting due to dirty pulg,I thought the plug would be white if it was running to lean? According to white brothers the pipe is made for stock 400ex jetting and the K-n-N should just allow for better air flow.I think if there was engine damage I would have more trouble than just starting the thing.Once I clean the plug ,it fires right up and runs smooth.I just dont want to cause damage because of a few bolt ons.

 

Had you ever checked the plug before the mods? Do you notice it bogging at any point through the RPM range? How many disks are you using in the exhaust? Have you checked to see if the choke is on?

 

Did not check before mods,only choke for start up/seems to run smooth /as far as disks just what came on it/the pipe is tuned for 400ex/just got done riding after cleaning plug and it is still black and dry/did have a few backfires while warming up. and coming to a stop.

 

Check the overflow tube for the float boal. It could have gotten clogged by some dirt, but that usually causes a very noticable bog. Do you have an Outerwear on the filter? Sometimes they will absorb oil from the filter and not let air pass through.

 

Do you notice the bike smoking at all?? Maybe you have fried it so bad that the rings are passing oil into the combustion chamber.

In my experience, a K&N increases your airflow SUBSTANTUALLY, which would make the thing run way lean. Again, I am surprised it runs at all with the K&N. However, the airflows limiting factor is the size of the opening on the snorkle, so unless your airbox is vented, that restriction may have saved you. I would have the jetting checked ASAP by an experienced professional!!

 

No smoke ever/Some backfiring when decel. /the pipe has 12 disks.