05' SPORTSMAN 500 A FRIEND WAS GONNA CHANGE MY MAIN JET FOR ME,AND NOW HE'S TOO BUSY NEED SOME DIRECTION ON HOW TO DO THIS PLS HELP.

 

It's just a matter of pulling the four screws out of the bowel (bottom of carb) to get at the main jet and swaping it out. What are you running fora main??

 

i currently have a 155 and am going to try a170 or 162.5

 

Why are you changing jets? Just putting a bigger jet is not going to do much for you unless you are running lean.

Most ATV's from the factory are jetted rich, putting a larger jet will more than likely make it run bad, especially at the top end.

No point in changing jets just for the sake of putting a different one in, you should change jets to tune your carb, to move it from a rich or lean condition. Then you have to do test at WOT and check the plug color, the best is a plug chop. If you don't do a proper test at WOT and the engine idles before it is checked then the results are not accurate.

A couple simple things that you can do is to run at a rapid speed and choke it a little if it runs better that means you are lean and probably could use a larger jet.
From full throttle if you rapidly back off the gas to 7/8 throttle and it runs better that means you are rich and probably could use a smaller jet.

If you are rich that doen't mean that you have to change to a smaller jet. It means that you don't have enough air. So you can incease the air flow by changing to a differnt type or air filter or change to a lighter oil on you filter or you can do some 'air-jetting' to get more air to your air box.

If you are lean then you can change jets or restrict your air flow in different ways. Close off part of the opening, wrap a screen around your air filter, put an old pair of panty hose (nulons) over the air filter, stuff extra foam in the filter, duct-tape part of your filter, anything to slow down and/or restrict the air flow.

If it runs good now then I would suggest leaving it alone, simply putting in a bigger jet will more than likely make a current rich condition even richer and it will run like crap.

 

<div class="FTQUOTE"><begin quote>Originally posted by: KBOB5

i currently have a 155 and am going to try a170 or 162.5</end quote></div>

You more than likely have a 34mm or 36mm carb and a 155 is plenty big for that size carb and 500cc, unless you have some hot cam in there, with an unrestricted exhaust. You would probably benefit more by increasing the air flow and also increasing the rate of flow (more air and faster air travel).

First you need to determine if you are running a rich or a lean condition at full throttle.
Once you know that then you make adjustments to correct it.

 

There are three stages to a carb, slow, medium, fast.
Or idle, mid-range, and wide open.
You can be either lean, rich or dead on with any combination.
You can be lean while idle, rich at mid-range, and lean at WOT
So basically you can have nine different combinations to deal with.
First you tune for idel with the pilot jet. (idle)
Then the mid-range (needle height) - (mid-range)
Then WOT (main jet)
All three overlap each other, meaning that when you are at WOT the pilot jet is still working and the needle height still helps and the main jet is doing most of the gas delivery to try and match all three with the air flow.

 

ok thanks for advice, i do have a k&n air filter in my quad, and all I really want is more power. What are some cheap and easy mods that u recommend?

 

<div class="FTQUOTE"><begin quote>Originally posted by: KBOB5

ok thanks for advice, i do have a k&n air filter in my quad, and all I really want is more power. What are some cheap and easy mods that u recommend?</end quote></div>

Is $6.00 cheap enough for a real noticable gain?
First thing to do is to determine if you are rich or lean. That would be the first step. More than likely you are rich because most all ATV's come from the factories a little on the rich side (warranty issues with melt-downs for factories to deal with). The cheapest way to get HP is to get more air into the air box (assuming you are on the rich side - if not then you can make it rich with a jet change) then 'air-jet' the thing. For about $6.00 it will make you think you have an extra 50-100cc's. You only get power from more gas - however if there is not enough air then the extra gas is useless. Things like K&N air filters don't give you more air they just increase the rate of delivery of the available air. Even a stock filter if given more air will produce more HP than just a high volume filter.