ok, i have a 2005 300ex, im getting a hmf sport series pipe( with quiet core), and a k&n filter. now do i absoluly have to run a jet kit to keep from running lean, or can i save the money and put it toward some razrs. my dad is always saying im better off not jetting, is he right, i want more power, but im fairly happy with a smal gain.

 

You will need to rejet. Its not just a performance thing, any time you are getting more air to the engine you are going to need more fuel. If you dont rejet you will be running lean and burn up your motor.

 

You will need to rejet, but you don't need to buy a jet kit. Hmf gives jetting recommendations on their website, you can find what they recommend for your 300, then go to a dealer or powersports shop and buy the jet for about $3.00.

If you don't rejet you most likely will actually lose power. To get maximum power your jetting ratio has to be perfect, when you add more air to the ratio, you also have to add more fuel, or your ratio will be off and you can lose power over the stock exhaust. Plus, even worse, running too lean causes overheating and in extreme lean situations can cause internal engine damage, like burnt valves, burnt piston rings, and even a hole in the piston. I think that's enough to justify spending a couple bucks on jets and a hour rejetting it. For as much money as aftermarket exhaust systems cost, I don't understand how people can pay $200+ on the silencer, but won't spend another few bucks to get the most power out of it.

 

He is exactly right, around here a jet is only $2.00 so don't worry about saving money by not jetting, do it right and prevent damage and help your power.

 

i see what you guys are saying but... if its sucking in more air would it not suck in more fuel through the slide, i mean thats where alot of the fuel is comeing from, am i wrong. and the hmf site has the specs for the slip on pipe, im getting the full pipe.

 

No, the fuel doesn't come from the slide. The fuel comes through the pilot jet at idle-1/4 throttle, the needle/hole at 1/4-3/4 throttle, and the main jet at 3/4 to full throttle. Carburetors are not self-adjusting.

You can contact HMF if they don't have jetting recommendations for your application, or you can use their recommendation for the slip-on as a baseline, and go up a size if you need to.

 

And how sure are you that you're getting a full system? According to HMF's web site, they don't even make a full system for the 300ex.

 

from what i understand im getting the full system, i'll reseach it though. thanlks for the help but i still may need a little more

 

ok you were right about the slip on/ full system thing, im fairly dissapointed, but oh well, i suppose i'll find another pipe, do you know of any other pipes that work for low end power? im just no satisfied with the slip on.

 

I don't really know for sure, but I think that big gun is a good low end pipe.