2006 yfz450 will not stay running after idle.

yes I was talking about the long needle that goes in the main. it will be loose once it lifts. mine was loose when seated. some but not all of the symptoms were similar. mine was popping and back firing but it was due to an extremely rich mixture and fuel collecting in the pipe. mine however was fouling plugs and not turning them white. you would have to do a side by side comparison with the old one to know for sure (assuming you changed it with your rebuild) you don't want to disable the tps in my opinion. one it will not cause the issues you are having and two when you disable it the cdi defaults to the wide open throttle timing curve. making the machine harder to start and reducing performance on the bottom end. checking it is fairly easy if you have a good ohm meter but you will need a manual for the specifications. don't get too hung up on the tors tps or the parking brake switch, they are just simple rule outs to help me rule out some of the electronic stuff. the fact that it ran before parked and now has issues normally says carb. electronics don't normally go bad sitting.there is a spring and diaphragm on the side of the carb, the name escapes me right now. did you check to make sure that is good when you did your rebuild. that can cause vacuum issues as well.

I put the new carb seal on that go's between the carb and the motor. It helped out a lot. She idles even better and sounds like it has a lot more power now.I had to turn the idle down a little because it wanted to run faster after the new seal was put on. I can hold rpms better but now its popping out of the exhaust 2 or 3 times per second but they are much litter pops. The plug is now a gray color.

I did start with a black plug and 158 main 42 pilot so I feel something is still letting air in.

I have been revving and holding rpms in neutral if that matters.

The only thing I can find on the carb diagram that looks any different then my carb is #32 Plunger, Starter mine has a o ring half way up the shaft on it and the diagram shows a o ring at the bottom of the Plunger, Starter My o-ring is wore real good but feels like it makes a good seal.

part numbers 32 and 34
2006 Yamaha YFZ450 SPECIAL EDITION (YFZ450SPV) Carburetor | Babbitts Yamaha Partshouse

you said in your first post a 168 main and in the last post you state a 158 main. did you change it or is one a typo. if it is a 158 main i think you are too lean. you should be up around 165. if you have the cash i would order the jd jet kit for it, they are about 80 bucks but i think it will fix the rest of your problems. it comes with a redesigned main jet needle, a selection of jets and instructions that guide your for your elevation and any future mods. it also give you the ability to easily re jet for new riding areas at different elevations. if i am guessing correctly your carb is factory stock. what you describe sounds lean and that would coincide with the factory settings. they are lean from the factory. if you cant swing the jet kit jump up to a 162 or 165 and see what happens. i am running a 170 with a pipe airbox mod and some mild motor work at sea level and i am a little lean. the diaphragm is part 81 and 82 but i think you found the problem and just need to fine tune the jetting. both of my yfz's pop and snort a little when you are holding rpm's in neutral