is it bad to rejet a stock bike

[sam the brave]

i put a 160 main jet in my bike and dont use the air box lid will it do any bad to my bike

[wilkin250r]

Well, if you remove the airbox lid, it's not exactly the same as "stock" is it?

There are reasons beyond just "more airflow" when you make even simple changes to the intake. The piston creates a vacuum through the intake path. The more restrictions you have in your intake path (like the filter, snorkel, ect) the more prevalent this vacuum is, basically the lower your intake pressure will be.

Your carb works by what is called the Venturi Effect. The intake is at a lower pressure than the carb float bowl. This is what brings the fuel up from the float bowl into your intake. Less pressure in the intake results in more fuel.

The piston creates a vacuum, so removing restrictions in the intake will increase the intake pressure. Many people think the only reason you need to increase jet size is because you have more air available, so you need more fuel. This is only partially true. You also need to increase your jet size because you now have greater intake pressure (less vacuum), so you need a bigger jet just to get the same amount of fuel.

[sam the brave]

oh so i am fine thanks