Help me get started on jetting!

[predrider305]

I was looking into learning how to jet a carb since it seems to be a very important part of the atv world! Found a few good pages about jetting and have a question. How would I increase the jet size on a pilot or a main jet? Would I have to buy new jets or is there a certain procedure to do so on the stock jets? Thanks.

P.s: try to lean any replies towards a beginners point of view

[DirtDemon]

You can drill jets out to make the orifices bigger, but generally, you just remove the old jets and install new ones. Obviously, there is no way to make jets smaller, so the only option for smaller jets is to change them. Changing jets is very simple, the main jet can be accessed through the drain bolt in the bottom of the float bowl, it just unscrews from the carb and you screw the new jet in. To get to the pilot jet, you have to remove the float bowl, the pilot jet sits just in front of the main jet. The needle is accessed fromt the top of the carb, the needle sits in the slide valve or piston valve, depending on what type of carb you are dealing with. A slide valve is manually moved up by a mechanical connection to the throttle, it controls both air flow and needle position, a piston valve controls only the needle position, as it moves up and down in reaction to airflow through the carb, in this type of carb, the airflow is controlled by a butterfly valve. In most slide valve carbs, there are grooves at the top of the needle, where an e-clip sits, moving this clip up on the needle for a leaner setting, down on the needle for a richer setting. In most piston valve carbs, the needle position generally fixed, but can be adjusted by a washer. Generally needle tuning in this type of carb is done my changing the spring that holds the slide vavle down, or by drilling out the holes in the slide vavle.

[predrider305]

So if I want to buy jets, will the size be optional, or does the kit come with multiple sizes? I need a smaller main jet, and i was wondering if it comes with multiple sizes in case I get an exhaust or something later.

[DirtDemon]

Most jet kits will come with an assortment of main jets and a needle or two, maybe a few other things, but I think they only have jets that are larger than stock. If you buy individual jets, you can get them in all kinds of sizes, bigger or smaller. If you need a smaller main, then I would just buy the next couple sizes smaller than what you have. If you do any mods, or add an exhuast, then a jet kit may be of some use to you. Just curious, why do you need a smaller main jet?