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Yes correct, the slide is designed to wear out before the carb itself. The slide is made of Zinc Alloy, which wears out before the alum carb body. It usually takes alot of hours to wear a slide out, but it also depends on the maintence on the bike. If someone is bad at replacing air filters, etc. Or rides in a area with alot of sand or fine dirt. Its can wear a slide/needle out quickly. Anytime I buy a used 2 stroke, I do a top end, and replace the slide/needle and cable. Might be over kill but...

You will notice the JD gasket is stronger than the OEM. Lightly smear some grease on it to help hold it in place when assembling .

Give your slide a good look. If there is any wear, marks, etc. Replace it with a new one. Possibly your needle as well. Consider both of these pieces wear out parts.

You can also get them from Jets R Us. Carburetor jets, parts and tuning items - Jets R Us

What does the plug look like immediately after a hard ride? I had pretty much the same issue with uneven jetting - Main and needle were lean and the pilot was rich. It takes a little bit for the pilot to 'catch up' and richen a lean condition after holding it wide open, and this sort of thing will happen. Not saying that is your problem - but its something to look into. Try all of the above first.

JD jetting

Check all of the above first, but It sure sounds like something Is holding the slide up. Are you using the original carb and slide and cable holder or something else ?

" The bike revs up perfectly fine, no bogs, sounds very healthy. When letting off the throttle the bikes dips down to what would be the correct idle speed, but after 3-8 seconds it dips down way too low and it dies." This condition you describe is not a hanging idle. This is the opposite of a hanging idle. A hanging idle is when the bike is hesitant to return down to the proper idle speed and, instead, the idle "hangs" higher than it should, and then it won't die. It will sit there idling at a high idle, which...

My KTM with yz250 carb was running like shit. Turns out the cap to the carb that holds the slide and throttle cable had come loose. Must've gotten distracted in the garage and didn't tighten it down fully. Check your hose clamps that hold the carb to the airbox and reed cage as well. Might get you a propane torch from home depot and apply some gas to various places and see if it revs up.

Try blowing compressed air through this hole. Then clean/spray it with suspension cleaner or contact cleaner. Usually solves the problem when that happens.