My experience says if it revs on its own and falls flat when trying to rev the throttle then that indicates it is out of gas. My opinion you need to look at entire fuel system. Good luck. You will feel great when you get it figured out. Stick with it!

Well I have been working on bikes for a lot of years but usually nothing this old. So got bike figured out somewhat. The jet on the end of the carb drain bolt was plugged. I never knew anything about this jet guess you learn something new everyday. But now bike breaks up at 5k

That MIGHT be the main jet.

Anyway, great that you're making progress.

'Darreng' read back to my post regarding main jet, as everything except the pilot & choke suck via the main jet so is super important. So if it's now running up to 5 grand then breaking up [not fading away] that sounds more like a restricted exhaust in the spark arrester area deep down in the back section. If not that--then the little Oring on the emulsion tube extension into the bowl [fed from the main jet but bypassed if not sealing]. That theory doesn't hold water though because if not sealing then the blocked main jet wouldn't have had the same affect. So--back to exhaust!!. Audio of the breaking up is good if possible as we all interpret or describe symptoms differently.

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. . . watching

This post made by the ORIGINAL Enduronut . . . . . not to be confused with the new member "Enduro - nut"

Too close for comfort if you ask me . . . could create a lot of confusion!

Ok . . . got that off my chest . . . so, back to the problem at hand guys.

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What kind of air filter are you using

You should have copyrighted your username and all variations thereof!

Yes, I did look twice at the new "Nut's" username, but I'll be fine unless they start using your avatar!

Okay. No i haven't got a 360. I have a DT3 250 with the same problem. This is how it's gone.
I bought this bike from a forum member and he told me about the problem. It's not an issue with me nor him.
My initial thought was crank seal.
Bike fired up and idled, bogged down at the sudden whiff of throttle.
I thought maybe the carb etc.
Cleaned the carb out and found a washer missing from under the main Jet.
Replaced that and problem almost went. Mmm , Almost.
Enriched the mixture and there we are better again.
went to work and i'm away for almost 1 month at that time.
Went in the work shop kicked the bike up. Run sweet,went for a quick ride on it and as soon as it got ten or so seconds under stress ,problem came back.
I've fannied around for months with this and that and eventually it got to the point where it fires up and runs well on choke to idle only on start up .
Then the revs started to creep.
Cut a long story short it's turned out to be

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the crank seals.
Good luck.
Regards Dave.

Rt325 I found the problem why it was breaking up at 5k.. bad spark plug.. bike works good now other then I took it for hard run. After that it started smoking really bad and not 2 stroke smell exhaust is getting hot I'm thinking possibly exhaust is plugged? Or transmission side crankshaft seal?

Maybe the admins could add FN before the new guy's name, as in FNG: Freakin' New Enduro-nut! Or maybe add #14 before...#14Enduro-nut, a la Chris Godwin and Tom Brady...