need help with my 400ex

[brianteel]

It has been running great and the only thing is have done is changed the oil and plug. since about 2 weeks ago the engine is now bogging down still and misfiring. you can here the mis at idle and once you get on it it just cuts out. I cleaned the carb and replaced the plug and they did not help it. the only time this happens is once it gets warm. once it is up to temp it does this. has onyone seen this and could help.

mods:
aluminum air box
pro circuit pipe
jet kit (dont know what kind)
K&N filter

[walt miller]

check to see if you put the right plug in it. also how old is the gas in it or did you just put gas in it? you could have bad gas

[brianteel]

i had av gas in there (105+ octane leaded) I drained that cleaned the carb and refilled with new super. the plug is the right one and i tried 3 others that i have that are new. I have tried everything i can think of short of taking the whole motor apart. I am trying to find out if someone had the sme issues and maybe can lead me in the right direction....could it be a bad coil or CDI

[walt miller]

when was the last time you ajusted your valves? they could be out of ajustment and when it gets warm they are not closing

[brianteel]

we pulled the covers off and looked it...they appear to be fine. often do they go out

[walt miller]

what do you mean they appear fine ? did you check them with a filler gage are they with in limits? you should check them every time you change you oil.

[brianteel]

my friend was helping that knows a little then mine and he said they were fine. is there anything else to check besides that....remember it only does it once it gets warm. when it is cold it runs great...

[walt miller]

sorry, the only thing i can think of that would act like that would be you choke is on

[brianteel]

that is the way it is acting but the choke is off

[walt miller]

make sure your air filteris clean and also no biuld up of carbon in the exhaust. other then that i do not know. cdi that i have know to go out do not work at all

[Toadz400]

I'd check the valves, it sounds like your friend just looked at them and assumed they were fine because they weren't bent to hell. Get in there with a filer gauge and make sure they are within specs.

Try messing with your jetting also, could be on the rich side if you haven't rejetted it for the warmer weather.

[brianteel]

i am going to get a filer gauge and check....i know that everything is cleaned because it is the frist thing we tried and the jetting is good at this point

make sure the plug is properly gapped and make sure your 105+ octane gas is U4 and NOT C12, i bought C12 by mistake and it made my bike run horrible>>>>let me know if that helped any<<<<

[brianteel]

what is U4

Its a more reliable type of fuel, cleaner than C12. Ask the place where you bought the fuel they'll be able to show you the difference.

[Chino886]

Check to see that the plug is in all the way, mine rattled lose while I was at the dunes and it had the same symptoms as you are describing, check the threads on your head.

[brianteel]

it is av gas which is very clean because it is used in air planes...i get it for free and run it threw a filter....there are also 3 other quads running off the same tank