Jetting...I have no Clue!

Ok, I am learning one step at a time with all this stuff I am doing to my 82 KZ 750 Twin. So I put 2 to 1 after market pipes on, and it runs ok, but I am at 10,000ft. It backfires and I know I have to rejett. I also am about to put k&n filter pods on too. So, can you help explain this to me very simply. Do I physically need to buy bigger or smaller jets and put them in, is that what it means to rejett? Do you have any suggestions with what size jets to use, seeing is how I have pipes and want to put pods on and live at 10,000ft. And when I do all the things you tell me to do, will that take care of the backfiring or do I need to do something else or look somewhere else for that problem? Thanks for the help!

You are right about rejetting. It means that you either buy and put in larger or smaller jets to compensate for any changes made to the air filtering, or engine modifications, or changes in the exhaust, that will have an effect on the flow through the engine. And with the changes you have done, you will most likely need bigger jets.
The jet sizes used by others, with the same mods made to their bikes, might give you a hint, but there are only one way to find out what jet sizes that will work on your bike, and that is by testing them out. I would also wait with the jetting till you have put on the K&N filters, since they will most likeley require more rejetting if you don't wait.

I hope you will find this jetting guide helpful. If you scroll all the way down you will also see that it have an advice about jetting and altitude:

www.motorcyclecarbs.com/Jetting_Rules_of_Thumb_W43C551.cfm

But it will be a trial and error issue. And don't make more than one change at a time. Otherwise you will loose track of what you are doing. And personally I have found that CV carbs are running just as well, even better, on my 400 twin, with the stock air filter box.

Anyway, good luck.

Personally I would keep airbox. Unless you are building a hotrodded bike I would keep it for the reliability factor. Do you have access to a dragstrip near you. The only way to jet correctly is to run full open throttle for at least a 1/4 mile with new plugs. Using kill switch shut off motor (do not close throttle first). Coast to a stop and check plug colour. White(ish) to lean, tan to brown(ish) just right, dark to black to rich. This will get you real close on main jet. Idle and pilot circuits are another story. You will have to go up 1 or 2 sizes on your mainjet. Likely 2 because of extra altitude.