OK so I have a 98 xc 600 and all carbs ,needles, jets are all new n were set at dealer so my problem is its only backfires when choke is all the way down or off and it bogs on take off to and wet plugs ... But if I leave the choke on half way it doesn't backfire or bogs but I can flip choke off once I'm going and no problems at all ... Where do I start????

sounds like a blockage or water in the carby
clean out the main jets

1 = Check between carb and head for vacuum leaks
2 = Float height could be set to low
3 = Needle height low

Give the carb a good clean with carb cleaner making sure all passages and jets are clear. Reset float height and make sure all flanges seal properly.

The number 1 problem with ATVs is the carburetor. This could be a mixture problem... too rich will cause backfiring and difficulty starting as the carb needs more air. Try leaning it down a 1/8 turn. The choke is always intended to be used when starting; if you don't need to use the choke, the card is definitely running too rich. If you can't adjust to make it behave properly, then rebuild the carb, It's not difficult.. get a new throttle spring and float too. Ensure you place the keeper clip on the correct groove of the needle valve... where the throttle cable connects. Replace all the jets and gaskets... don;t get them mixed up. One larger jet is the primary jet and the smaller one, is the secondary. Get new screws, if the screws are a bit dog eared. Write down your previous mixture settings and start from there to adjust the mixture for starting and assure a slightly skipped idle. (Don't worry as you add throttle it will run smoothly.)

if you are running the engine at full CHOKE, then it is flooding the engine, but if you meant off full choke, then the carb is still stopped up. Try soaking in carb cleaner overnight after removing jet & all rubber goods. HOPE THIS HELPS.

Runs better with choke means the mixture is lean,
Has the exhaust been changed.?
Did this problem just begin.?
Check for air leaks on intake manifold.
Clean carb.
Check valve clearances
raise the needle jet one notch
one size up in the main jet.

check one item at a time, and write notes about jetting changes.and improvements
I also run Moreys upper cylnder lube, helps starting hot or cold, and helps stop "cough stopping" with heavy rear brake use

If your bike ran good previously - and nothing has been changed that would require rejetting or a needle adjustment, I would look for problems elsewhere. Such as:
Has the bike been stored for more than a few months at a time? If so, the carburetor jets could be plugged with fuel varnish. Only being able to start with the choke applied - and an inability to idle are both classic symptoms of this. Remove and disassemble the carburetor. Clean it and the jets out with carb cleaner and compressed air, then reassemble. Also make sure the fuel in the tank is fresh and that the fuel strainer (usually with the fuel petcock) is clean.
There are three ingredients required for combustion: fuel, compression, and a spark (at the right time). So long as you've got each of these - it has got to run.

Your primary jets in the carbs are clogged. (FYI- each carb has three metering jets, a primary, the needle or butterfly and the main jet. Each jet has an RPM area where it controls.) Simply blowing them out will not fix this problem. The carbs need removed and properly cleaned, the jets need to be probed and cleared then a new fuel filter installed to prevent it all from happening again. best wishes.

An air leak somewhere between the carb and the cylinder can cause the RPM problem. Tighten the mounting bolts. The carb may be clean but there is still a problem on the inside. Possibilities include plugged main jet, and/or needle jet. Also an incorrect needle jet setting. You have a very sophisticated carburetor. If you have already cleaned the inside of the carb I would let the dealer check it out.

Please rate this answer. Thanks kschomig!