jet kit?

[jon341427]

what is a jet kit? and what is its purpose? whats the difference between a slip on exhaust, and a regular exhaust? and lastly is a seat cowl a replacement for the back seat? or does it just go over the rear seat?

thanks, jon.

[UberGoober]

A jet kit changes the gas/air mixture in a carborated bike. A lot of bikes are tuned in the factory to be lean so they can meet emissions requirements - the trade off is less power. Changing the jets can "fix" that. Also, when you tweak the exhaust by putting on a different pipe you change the amount of air the engine flows and so you need to correct the jets so the bike gets the correct amount of fuel.

Really "tuning" the jets on a bike is like any scientific process. It is step by step and requires a dyno. If the bike is too lean it doesn't make as much power as it can, likewise if it is too rich. Tuners put in jets, run the bike on a dyno, swap them out, and measure the difference. They keep doing this until the bike makes max horsepower - they find this out when the previous dyno reading is higher than the current one. Then they switch back to the previous set and are finished.

Fortunately for us shadetree mechanics, most the pipe manufacturers do this testing and if you research the kind of pipe you want, they will recommend what size jets to use. Fuel injected bikes, by the way, don't need to be re-jetted - you load a new performance profile into the computer.

A "slip on" is a muffler you buy and change off with your stock one. You just cut your can off and slip on the new one. The alternative to this is a full system wich means you change the whole exhaust from the cylinder head right out the back. I've never used a slip on, all my bikes (except my first - which was stock) have been full systems. Slip ons can help increase the amount of power a bike makes by increasing amount of air the bike flows - the trade off is increased noise and emissions. Personally, I'd trade the full race exhaust my current bike has for something quieter.

On the seat cowls, I think it depends upon the bike. Most of the one's I've seen require the removal of the rear seat but I imagine there are some that are just covers.

[RayOSV]

Originally Posted by jon341427

what is a jet kit? and what is its purpose? whats the difference between a slip on exhaust, and a regular exhaust? and lastly is a seat cowl a replacement for the back seat? or does it just go over the rear seat?

thanks, jon.

A jet kit is a collection of parts for each carb to alter the air/fuel mixture for improved engine performance. Usually only the main jet is changed along with some internal carb adjustments (idle mixture screws, needle clips, etc.). All of this may sound a little mysterious, but if you look at a parts diagram of a carburetor it will become more clear. Bikes are set up to run lean from the factory to pass emissions regulations. Making the bike draw more air by less restrictive air filter or exhaust causes it to run more lean. Re-jetting richens the air/fuel mixture for better performance.

A slip-on exhaust is just the "muffler" or canister part and doesn't include all the piping from the exhaust port on the engine to the canister. A full exhaust includes everything. Again the goal is less restriction in the exhaust path.

Yes, a seat cowl is a plastic part that replaces the rear seat. Purpose is for looks, more "trunk" space, and an excuse not to carry a passenger.

[zx11_12]

I know that my Zx-12R seat cowl was a cover. My CBR1000RR replaces the seat. Honestly, I like the CBR cowl better. it's much easier to use then trying to get the cover on and off the seat on the ZX-12R. You might think that having a cover would be more handy, since you always have your seat if you meet some cutie who wants a ride, but when you take the cover off, what are you going to do with it? You have to leave it somewhere, so there is no real advantage to it.

[jon341427]

thanks everyone.