Question regarding a 2001 300EX - I am just staring to make modifications. I have one year of college left and money is rather tight.

I realize that drilling holes in the air box increases the air flow, but is it necessary to re-jet and add an aftermarket pipe? What are the effects of only drilling holes? Will there be a noticable difference? If so, how many are required to see that difference? What are the advantages and disadvantages of buying a used aftermarket pipe?

 

I have a 400Ex and I put a big gun slip on pipe on it and a Dynojet jet kit. I dont know witch one needed it more but I had to take the air box lid off for it to run right. I seen a test where they drilled 6 1 1/2in holes in the lid and that was just with the jet kit. There is a company that makes a kit with 6 1in plug filters that drop right in the holes for like $8.00 good luck.

 

The only way I know of to get some free HP is to gut the stock exaust. Take all the baffles and packing out of the exaust. Drilling holes in the airbox will help your bike breath easier, and will help out somewhat but, nothing you will notice. You make even be able to go up a jet size or two once you gut the pipe.
Stick to the schoolin, and you'll have plenty of extra cash for the add on toys.
Good luck

 

I thought "money ain't no thang". Here is your reply to ex_master at 1:02pm 4/25/01,
quote:"keep'n it simple" would restrict us who want more. keeping it simple would only limit us from what we enjoy. SPEED, POWER, and TECHNOLOGICAL ADVANCEMENT. These advancements allow us to explore what the maximum capabilities of our machines have.
I do agree with you when stating that it is getting expensive. But, if you have to love and passion for it, money ain't no thang!"unquote.
nuff said.

 

...don't drill holes... just take your airbox lid off. Put it back on if you plan to ride on sand- but other than that- you'll get a noticable power increase. The reason people rejet their bikes is because when you mess with airflow- the air/fuel mixture will be off. So taking your airbox lid off will generally result in a larger jet size. Putting in a larger jet is really easy- anyone can do it. You'll get an additional gain in HP when you rejet as well.- and your throttle responsiveness will be better.

As for aftermarket pipes- this is a good HP gain-and they make your bike sound bad-***. There really isn't much of a difference between the big-names in terms of power gain. (many will argue with me) but the difference between all of them is VERY small. I went with the White Bro's e series slip on- and I LOVE this pipe.

hope that helps

 

Rotgut

I have a 170 jet in my 400EX and it wont hardly run after about 1/2 thottle with the air box lid on does yours do the same with the 165? I have been thinking of changing it.

 

A 170 jet seems pretty big for a 400(depending on your mods and altitude)Ive got a 440 and Powroll(who did the work) recomended a 165 even after all the mods.Ive tried larger jets but a 165 or 168 seem to work the best for me.

 

I have a big gun slip on and a k&n filter with a Dynojet jet kit. It recomended a 170 for my altitude (I live in KS) but I would think it would run ok with the air box lid off is that comman?

 

Here's the deal...

If you have a jetting problem... your machine will run like crap- and it's noticable! Try different jet sizes and give your engine time to warm up with each try. You will know it when you hit the sweet spot. It sounds like 170 is too high. Drop 2 sizes and see what happens. After that... run you bike with the box lid AND filter OFF. Then run it with the filter duck-taped 1/3 covered. If it runs crappy either way... you found the right jet size. If it runs better with out lid/air filter... then you need drop to a smaller jet size.... You'll need a bigger size if it runs better with a taped filter.

It all boils down to fuel/air mixture. It has to be perfect.

 

this reply is for the original dude.
if you drill holes in your air box or remove the lid, you should re-jet or the bike could run lean. jetting your carb is easy, takes about 20 minutes, because you have to remove the plastic and stuff. you could get good power increse with the air box lid removed and a stock pipe as long as its jetted properly.