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Discussion Starter #1 (Edited)
Hello friends. I recently installed a new HMF Performance Series Exhaust on “Sonic”, my 01 Raptor 660R. Also rebuilt the carbs and installed an HMF-supplied jet kit, following the HMF jetting recommendations. Just getting it back together. Running stock airbox and filter setup - all cleaned last night. Tonight after changing the oil I started the machine and let it run/idle for about two minutes. Started it with choke on, then quickly went to choke off. Head pipes slowly began to glow orange. Not brightly, but dimly glow. Is this ok? I know I saw a brand new YFZ450 at a dealer glow the pipe bright orange when I idled it for a few mins.
 

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The thinner aluminum these pipes are made from will glow slightly, but if they are bright orange then I think they are running too lean at that point.
 
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They will get hot and glow at times, especially at idle.
Idle afr is usually pretty lean as well as no air moving over the tubing to cool it off.
 
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Discussion Starter #6
They will get hot and glow at times, especially at idle.
Idle afr is usually pretty lean as well as no air moving over the tubing to cool it off.
Thanks. In your opinion and from your experience, is it worth adjusting the idle afr to richen up a tad?
 

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Thanks. In your opinion and from your experience, is it worth adjusting the idle afr to richen up a tad?
No. If it’s running well, leave it.
Should be #25 pilots somewhere in the 2-2.5 turns out on the fuel screws.
 
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Discussion Starter #8
No. If it’s running well, leave it.
Should be #25 pilots somewhere in the 2-2.5 turns out on the fuel screws.
If I recall correctly, I don't believe the HMF kit came with new pilot jets, so those are probably still stock...I don't remember what size they were. I did go up to 145 left and 150 right main jets.
For what it's worth, I live at 5600 ft elevation.
 

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The stock pilots are 22.5, and you are correct, they do not come in the jet kit, they must be bought seperately and individually.
Sorry, I have no experience with high altitude tuning either, as much of it seems counterintuitive to tuning at sea level to a couple thousand feet above.
 

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At a mile high with lid on airbox, I think stock pilots are probably okay. You could swap to the 25s and see if it gets better, can always thread the screws in a bit if needed.
 

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Discussion Starter #17
At a mile high with lid on airbox, I think stock pilots are probably okay. You could swap to the 25s and see if it gets better, can always thread the screws in a bit if needed.
Riding today, I can now definitely say something is off. In the bottom end of the throttle, opening off of closed throttle, probably first 3rd of throttle play, it sputters and bucks and can't decide if it wants to scream or cough, crack it open and it comes to life beautifully. It also idles well. But put the motor under load and it will not run well in the 1/3rd of the throttle play. ALSO it backfires after turning it off. Like 1 full second after shutting it off it pops out the muffler. I've never seen that before. I wish I remembered where we set the afr screws, but I don't. I think we set them back where they were! With stock exhaust it was running fine. I know we reused the stock pilot jets. I'm obviously going to have to pull the carbs again - dang it - and I'd love to get it right on the next try. Suggestions welcome. This Raptor is so fun, I can't get enough of how hard it pulls in all 5 gears. BIG SMILE on my face.
Stock air box/intake/filter - all clean.
145/150 main jets
Stock pilot jets
HMF full Performance Series Exhaust
 
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