i have a nt650 with a muzzy exhaust system ,stock air box , could someone what carb jets to use it seems to run ok the way it is but some times when i rev it and let off it pops a couple of times like it is lean but when riding it runs great. thanks

Unfortunately, each and every engine, air filter, carburetor, header, and exhaust can combination is different enough that there really isn't any recipe for any given set-up that will provide perfect results.

People with similar set ups can provide you with a good starting point. However, to expect to have someone, even with the exact same components as yours, provide you with jet numbers and have it be perfect is a very long shot.

It does sound like it is lean, although it could be from an air leak and not carbureation.

First, check that all of intake boots are mounted correctly and that they aren't old or cracked.

If they look fine and are mounted properly do the following to make sure that there isn't a leak. Ride the bike about 20 minutes or so until it is up to operating temperature. Then while sitting, at idle, hose down the carb boots and the intake boots on the carb with WD 40. If the idle changes in any dramatic way, you have an air leak.

Are you using the stock air box or pod filters?

If you are using the box, inspect it for cracks or leaks.

Secondly, have you done a plug chop and looked at the condition of the plugs?

To do so, find a quiet stretch of straight road where you can pull off safely.

In first or second gear (just because you'd end up going quite fast in a higher gear), run the bike at full throttle until it gets just to the red line. At that moment, pull in the clutch and hit the kill switch simultaneously.

Then, stop the bike and DO NOT START IT AGAIN (just yet). Unscrew the accessible plug in both the front and rear head and examine it. The white ceramic part should look like a properly toasted marshmallow. Dry, but a bit brown. Too white, and you are too lean. Black and wet, too rich.

Getting it to that nice toasted marshmallow color will get you about 95% there.

Hope this helps

Nice advice Ryan.Remember-0-1/8th pilots/2/8-7/8ths needles/8/8-mains-this is a good way to Sherlock where it's lean/rich.

ryan i changed the intake boots and iam sure there are no leaks , i have the pilot screws at two turns out it runs strong ,all the way to 8500 rpm ,so maybe i should just leave it the way it is. thanks for the help

A little detonation on decel is OK.Leave it for now.