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I know a ton of people have posted about this as i have been reading the forums about others that have had questions, but I have not come across anyone with a problem like mine.
I purchased a 400ex about 3 months ago, It is a 2000 , it had a White Brothers pipe on it and a K&N filter , with the lid still on the air box and no holes drilled in it, I checked the main jet after i got it home and it had a 146 in it, I then replaced the plug and ran it for a bit , then checked the plug and it was a nice tan brown.
The pipe then cracked on me about a week ago , so I decided to replace it with an HMF slip on (the white brothers also a slip on), after I put it on I replaced the plug and ran it for a bit with the 146 and of course it was lean, so I went to a 155 then a 160 then a 165 then a 170, then a 172 then a 175 then a 178 and now have stopped at a 180, all with the same results very lean , plug is always coming out white or light greyish, I have checked for air leaks and have found none.
I am checking the plug by firing up the bike then putting down the road in third gear , then turning around and then i go full out through all gears till I hit 5th and i'll hold it wide open for a few seconds(4-5) then pull clutch in and hit the kill switch , let it cool down , pull plug and check colouring of it.
If anybody has had any similar situation or any advice at all , I am open to anything, I am stumped.
Thanks
GregT
 

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I know a ton of people have posted about this as i have been reading the forums about others that have had questions, but I have not come across anyone with a problem like mine.
I purchased a 400ex about 3 months ago, It is a 2000 , it had a White Brothers pipe on it and a K&N filter , with the lid still on the air box and no holes drilled in it, I checked the main jet after i got it home and it had a 146 in it, I then replaced the plug and ran it for a bit , then checked the plug and it was a nice tan brown.
The pipe then cracked on me about a week ago , so I decided to replace it with an HMF slip on (the white brothers also a slip on), after I put it on I replaced the plug and ran it for a bit with the 146 and of course it was lean, so I went to a 155 then a 160 then a 165 then a 170, then a 172 then a 175 then a 178 and now have stopped at a 180, all with the same results very lean , plug is always coming out white or light greyish, I have checked for air leaks and have found none.
I am checking the plug by firing up the bike then putting down the road in third gear , then turning around and then i go full out through all gears till I hit 5th and i'll hold it wide open for a few seconds(4-5) then pull clutch in and hit the kill switch , let it cool down , pull plug and check colouring of it.
If anybody has had any similar situation or any advice at all , I am open to anything, I am stumped.
Thanks
GregT
The slip on should be jetted at about 165 to 170, air lid off, one notch down from stock setting on the needle clip, 2 turns out on the air screw, and a 40 to a 42 pilot jet. Go to hmf web site and print the directions out. As far as a chop check on the plug, just put it in first and rev it up then hit the kill. You dont need to go threw all the gears.
Nick

p.s. good choice on your new pipe, i love mine.
 

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HMMM??? This is a good one. Have you cleaned all the air/fuel holes in the carb? Only thing I can figure is that its sucking air. With that setup a 152 should be good. Let us know what you figure out.
 

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where have you checked for an air leak? Around the carb and intake? What about down the sides of the head or by the exhaust? A blown head gasket can suck in air before you here it blow out exhaust. Just a thought, hopefully I'm wrong but I've seen it before.
 

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165 to 170 is the normal for bolt on mods. the air screw is set at 3 turns out from lightly seated. and if it has an aftermarket needle set it to the 3rd ring. the 40 slow jet will aid in cold starts but a stock 38 is fine. also if you are running race fuel your plug reading will be alot leaner than pump gas. run a plug check with the lid on then put in a new plug and run it with it off and compare. Make sure you are at operating temp before running any test.
 
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