no difference with or without airbox lid

[esadagi]

I have a full pro circuit t-4 exhaust system and a uni filter with a k&k outerwears airbox cover. After cleaning the quad I put the stock airbox lid on to see what difference it would make expecting the motor to cut out. It seemed to run the same as with the lid off. This does not sound normal to me. Any ideas ? The quad is a 04 400ex. The plug looks great. It needs the choke to start and keep running for a couple of minutes, but after it is warmed up it runs excellent. I was just wondering if i had other problems.
Thank you.

[jeremy_283]

my quad did the same thing and my friends quad has done the same....... my friend went from running airbox with lid to no airbox at all cuz it broke ........... i just removed my lid ........... look at your plug tho........... rejet anyways........... ur prolly runnin lean and gettin your motor hot.............. but it seems weird that alot of peoples 400ex's do that .............. rejet though ....... or at least verify its jetted right ......... look at the How To's section

[GPracer2500]

Not everyone can discriminate small differences in airflow and jetting. Sometimes it takes a very keen sense that must be developed with experience.

If your bike seems to run well whether the airbox is off or on then your jetting is probably just a little lean with it off and just a little rich with it on--but not so far off in either configuration for you to tell the difference.

[esadagi]

thanks for the input. I will leave it off then. Do you think it needs to be re-jetted then ?

[2004exrider]

You probably need to go a jet size up unless you were a little rich before you removed it, but check your spark plug. I could deffinitely tell the difference in throttle responce when i removed mine. If you have the proper jetting it will feel a little different. But i put mine back on because it wasnt worth having all the extra dust and water that got in there.

Jimmy

[DANVAN]

After reading this I went out and removed the lid from my 300, Boy I felt at difference at low end, But I think it ran out of top end a little sooner, I will retest next time with the lid on to confirm that.

It sounds sweet with the lid off too.

Im thinking I may end up drilling some holes in the cover so that I get some extra air but not too much that it runs out of top end.

[bradrenea]

Originally posted by DANVAN
After reading this I went out and removed the lid from my 300, Boy I felt at difference at low end, But I think it ran out of top end a little sooner, I will retest next time with the lid on to confirm that.

It sounds sweet with the lid off too.

Im thinking I may end up drilling some holes in the cover so that I get some extra air but not too much that it runs out of top end.

If you jet it right it will not "run out of top end".
If the jetting is correct it should have more power throughout the RPM range, but especially on top end.