OK I want to preface this post by saying I am not a racer i am just a weekend rider and Iam not looking to make my quads in to racers. I just want to add some performance to them.

So with that, I want to know the real truth about intake and exhaust on a quad.

I have two quads, a KFX400 stock and a 250EX Stock.

Both came with foam filters and I have since replace the foam filters with UNI Foam air filters. I havent had any problems that I can tell.

Now I want to change out the Slip-On Silencer only. I am planning on the T-4 Pro-Circuit Silencers.

The Question I have is do I really need to re-jet when I put on a new Slip-on Silencer and a aftermarket foam filter?????

If so WHY? If you dont re-jet what happens after adding the above mentioned upgrades??

On a Car if you add a different filter like K&N and a different exhaust you dont have to do any thing to the motor to add more fuel.

Or is re-jetting a way for these permance shops to squueze more money out of you.

Well I hope some one can give me a straight answer on this.

Thanks...

 

And your solid answer is..............................maybe.


This is not true most of the time on a carb'ed car. If it has fuel injection, the computer will compensate for the increase in flow. Almost all carb'ed cars on the road go richer over time. I would guess that 95% of carb'ed cars on the road today are rich. So if they put a filter and exhaust on them, it will put them about right in the ball park mixture wise. They think "man that filter made a lot of HP." When in reality, the engine is in a better state of tune and that is where some of the HP came from.

I can only answer your question with a question. Is your mixture set "on the money?" Is so, then yes, you are going to have to jet up. If you are a little rich, then no, you will more than likely be ok.

An engine is nothing more than an air pump. If you add more flow (air) you have to add more fuel. If you don't, you could get things too lean and melt a piston or other "bad" things can happen.

 

Why do people constantly post this question???? The whole point is to achieve more performance. When you add more air, you have to add more fuel to keep the air/fuel ratio correct. If you don't have to rejet, you didn't achieve anything by doing the mod, except wasting money for no increase in performance!

For instance, going from one foam air filter to another didn't make much difference, so you GOT AWAY without a rejet. When you add a K&N or muffler, you will DEFINITELY need a rejet. Without it, your engine will run LEAN (if it runs at all), and it will overheat and your engine is toast. Don't try to be a cheap b******. You paid thousands of dollars for your bike, why not protect your investment? Pay for a rejet by a competent mechanic!

Your fuel injected car, automatically compensates for changes in air intake. Your carburated quad, can't do that on its own.