running way lean!!!!!HELP!!!!!

[EXDUNER127]

I need help my 400ex is running way lean, i havent ridden it in a few months, maybe 4-5.....anyway i took it out this weekend and it wont idle and when i get it going it keeps backfiring...loud...and runs way lean, and i had just recently cleaned filter from last riden because it was filthy, could that have any thing to do with it, i am running it with a main 170, stock pilot, full exhuast, k&n w/no lid, no choke. help why would it back fir eand not idle?

Put the lid back on and take it fer a spin and see if it takes away the backfiring. If so drop you main jet down a size or 2..

[JOEX]

Check for air leaks, intake and exhaust. I don't know if this makes a difference, is the gas old?

Joe

[cals400ex]

are you using keihin or dynojets? you could be lean on the pilot with that being stock. also, you may be lean on the needle if it is cold outside.

[hondarider2006]

Make sure your gas is good...this seemed to be the problem for me...

[400Ex_Rida]

Try a 155 main jet

[400Ex_Rida]

155 with the lid on, 160 with lid off, it works for me

[quad_racer_19]

if it wont idle maybe clean your ports, i had that to get done with my sled, while it was there i got it ported and polished :D

[Scott-300ex]

yeah, i would say put your airbox lid back on

also, make sure you put oil on your filter too, cause that could make a difference

[northeast400]

I ran so lean this weekend my header started to glow

[cals400ex]

was it glowing at idle, mid throttle, or full throttle?

[cals400ex]

i noticed that mine didn't glow at idle or full throttle, but did anywhere in between. this indicated i was lean on my needle. i moved the clip down one position and the problem was solved.

[MDE3]

An exhaust leak at the ports will cause both of these phenomenon.

When you leak air into the cylinder through the intake stroke(while both sets of valves are open briefly), it reduces the velocity of air through the carb, drawing less fuel, and the air being drawn in at the exhaust port leak, has no fuel...hence it runs lean. Because of the improper fuel/air mix, the combustion is less efficient as well, for the fuel that is drawn in, and the unburnt fuel ignites when it gets the extra oxygen from the air leak as it accelerates down the pipe creating a venturi effect and drawing fresh cold air into your exhaust pipe and into the exhaust stream.

[skemp]

Just sounds like chit gas to me.