no lid vs. vents

trailripper1500

New Member
Feb 16, 2008
328
3
0
Hope Valley RI
right now i'm running my blaster w/ out the airbox cover w/ regular stock jetting. i put a book sock over the airbox to act as a dual filtration system, but i don't know if vents on the lid are better. let me know. p.s. i have all stock exhaust, but am soon getting a toomey b1 pipe kit, so what should i do when i get that?
 
i would only ditch the lid if your getting an aftermarket exhaust cuz you have to rejet, as suprex said, without it and with the stock exhaust. and it depends where you ride, i got a toomey exhaust and it gives you vents but i just took the lid of instead because less sh*t gets into your air box.
 
rejeting means you need to get a larger jet than stock. i think a 260 main jet woul be good
 
There is a formula for calculating the air demand of a motor...

A = CID * RPM / 20839

A = effective filtering area (square inches)
CID = cubic inch displacement
RPM = rev./min. at max power

In a stock blaster, 200 cc=12.2 cu. in.
So A = 12.2 cu in x 7000 rpm/ 20839 = approximately 4 square inches of filter needed
In this case, you would need 5.09 1" round vents in the airbox lid to accomodate the needs of the motor.

Running no airbox lid is unnecessary. You can achieve more than adequate flow with air box lid vents and still have the protection of the lid.
 
You are not benifiting anything witht he air box lid off. If you can't push the exhaust out your not going to pull any more in. As other have stated once you get your new exhaust on then you must modify the air box or remove lid and re-jet the carb.

The jets are super cheap..just a few dollars each. I would suggest having someone that knows how to do this and you watch to learn. As stated it's not hard but if not done correctly it's way to easy for the engine to go POP! Get a service manual it's a must for you just starting to undertand how these things work and tweak them.
 
toomey sends u a 310 main jet with the pipe but i would put lid back on until u get pipe..they also send the vents like 8 of them or some sh*t 1" so what lid would really have left anyways..
 
what if i adjust the air/fuel mixture screw? how much does one of those jets cost? i'm getting a toomey exhaust soon.

if u get the full B1 kit it comes with a 310 main jet and tells you how to install it, and it come with the vents too for the airbox
 
i'm getting the pipe sometime this summer so i'm gonna leave as is for now. it seems ok to me, plus my trails aren't very dusty right now or anything, so nothing should happen..i don't race or anything like that, so i don't put that much of a strain on my engine, so it should be fine for the time being.B-)
 
It is basic, hickskateboarder....but it does illustrate that it would be hard to undervent the stock airbox lid even with mods.
Personally, I like the idea of having a vented lid as a first layer of protection against mud splashing onto my filter.
Think about the diameter of the carburetor...doesn't that really pose the restriction on how much air the engine can flow no matter what? Even if you had double the area of the smallest inside diameter of the carburetor to overcome any frictional losses or turbulence in the stream, you would still not have an airbox full of holes...

I will say that this formula is intended for naturally aspirated motors, not forced induction motors for sure...

If I lived and rode in a less muddy area, I would probably not run a lid either.

Either way, as others have mentioned, the motor still needs to be rejetted if the amount of air flowing through the carb has changed...
 
k just so u admit it. lol j/k. i just mean things like aftermarket pipe, reeds, size of stroke/ports/carb, filter material and so many other things play a factor, but i get your point. haha but it does make a noticeable difference when u take the lid off, so it can't be getting all the air it needs (or wants!) thru that little snorkle.