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2001 520SX hesitates at high, level rpm

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Hi all, just got a hardly used 2001 520SX. Problem is it has a terrible hesitation/stumble at high, level rpms. Acceleration is good. I've cleaned the carb twice and set the float level to 9mm, nothing changed. New plug is in the mail. Just checked the infamous auto decompression bolt, it is nice and snug. I wanted to consult the experts before checking/replacing anything else. Any suggestions would be greatly appreciated.

PS: I live in Saudi Arabia. Yes, it is hot!

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I am not an expert by any means, but... hot air temp = thin air... this could be a jetting issue... how hot are we talking about? 110, 120? My friend just got back from Iraq and said it got to about 130 some days... your jetting is my best guess...

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I originaly suspected the jetting as well but as it turns out there are other KTM RFSs in the area that run fine with factory jetting, needle position, etc. Also, this stumble is quite severe. The bike is very jerky at high RPM.

BTW: Temps reach around 115 F.

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Don’t want to teach my granny to suck eggs, but while you were cleaning the carb did you blow out all the jets, if there is a small piece of grit still in there you will get probs. Also have you checked your air box for grit between the filter and the carb? If there is grit in there it can easily be sucked in and cause problems. Was there grit and or water in the bottom of the carb bowl when you stripped the carb?

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This bike had been put in storage immediately after original purcahse. I had to clean the carb because the fuel line had dissolved and when the guy finally rode the bike all that dissolved rubber collected on the screen just inside the carb. I blew out all the circuits both times I cleaned the carb. The air box is clean on the carb side. The general consensus seems to be that the carb is causing the problem. I will clean the carb again today to be sure I got all the grime. Thanks for the advice, keep it coming!!!

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Well Dave, I owe you a beer. I cleaned the carb again today after I adjusted the valves. I also moved the needle all the way down, changed the main from 175 to 172 and set the float a little lean. It runs better now but still cuts in and out pretty bad at high revs. I have a new plug on the way and will order a JD kit. Anyone have any other ideas?

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Well, put in the JD jet kit, no change in performance noted. I hope those spark plugs get here soon!!!

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