gota 03 400ex. it has a k&n with small holes in the lid. and a slip on lexx pipe with spark arrester. pulled the carb today because i had a stumble that would come outa nowhere. would be running great then all a sudden just fall on its face and barely idle. took carb apart and cleaned it. also hada black film on the piston looking thing inside the carb, and was really dirty when i removed the top cover. noticed the 38 jet seemed a little clogged but not sure if that was the problem, although its not done it anymore since re-installing. but ive also only ridden it for about 20 mins. will know for sure tomorow. anyone experienced this before? also i noticed my jets are stock 38/146.
but it runs perfect with the mods listed above. is this ok or could it still need jetting?
thanks
andy

 

mine was doing the same thing here a while back. I got to lookin and i found out that the rubber intake was cracked and it was sucking air. You might want to check that out because i took my carb off and cleaned it and everything before i found out what it was. just a thought.

 

Yea i didnt even think to inspect that, ima take it for another ride tomorrow and see if its still running right.
Should the piston inside the carb be slightly oily? noticed mine was, so cleaned it.
And what about the jets anyone? runs great with k&n, drilled box and slip-on. stock jets.is this ok? or should i still try bigger jets? if so whats a good starting point at sea level?

 

been reading and my stock jets should be 38/148 correct?
but it has 38/146 in it. with filter and pipe shouldnt it be running lean? dont wanna ride till i get this straight after reading about burnt pistons.
also, whats your opinions on removing the choke? worth it or not?

1 other thing, the drain tube from the carb was facing up and not hanging out the bottom. and should the drain srew be tightened completly? will that cause a problem when wheelieing?

 

could it be a aftermarket jet biengs its a 146. the holder looks like 2 nuts stacked up then the 146 jet screws into that. is this a stock or aftermarket setup or are they the same. the previous owner had a slip on but removed it and i recently bought a slip on but it still runs good with this jetting setup. just not sure to leave it cause its running good or get jets from dealer and see what happens. also plug is greyish

 

its for sure lean. my 07 400ex has hmf slip on air box vents jetted at 42 155 dyno jet.you havent noticed popping after letting off the throttle?

 

yea theres a very slight popping after letting off. wasnt sure if the 146 was a dynojet jet or something. dont know why someone would put a 146 in. im gonna swing by the honda shop and get a 152 and 155 and see how that works. should i change the 38 to a 40 or just leave it be. idles fine. thanks

 

<div class="FTQUOTE"><begin quote>Originally posted by: gsjeepxr

yea theres a very slight popping after letting off. wasnt sure if the 146 was a dynojet jet or something. dont know why someone would put a 146 in. im gonna swing by the honda shop and get a 152 and 155 and see how that works. should i change the 38 to a 40 or just leave it be. idles fine. thanks</end quote></div>

id go with 42 pilot mine starts real good in cold weather.the pilot jet shouldnt affect idle unless its dirty.1 more thing you will probbaly have to adjust your idle air screw 2 1/2 to 3 1/2 turns out it varys on your set up.turn screw all the way in not super tight and start with 2 1/2 turns out till you get a smooth idle

 

whats going to a 42 gonna do. my pipe said to stay with a stock 38 and go to a 150-152 main. just curious what the benefits going to a 40- 42 pilot.

 

how cold does it get were you live in winter?bigger pilot means easier starting in cold weather. pilot jet is for start up and just off idle.it wont affect the way it runs.get what you want you asked for help i gave it.i know on mine 42 pilot works good