450 ? Not banshee but still yamaha

[itsjustagreat1]

Ok, I know its not a banshee, but aI have a friend with a yfz 450 and it has a HMF exhaust system. He sait when the weather was warm, it wouldnt idle. Now that it is colder it idles, but when you rev it up it pops and shoots flames out the exhaust. I told him its a lean pop. Am I right by thinking that, or could it be something else. I definately know that it shouldn't shoot fire, so I was just wanting to help him out. Can anyone give me some ideas? I would have checked the plug, but he doesn't have a wrench, and is ordering one so we can get the plug out. If anyone has any suggestiones on jetting sizes for 2000 feet with the exhaust, that would help and also mabe some ideas on the problem. Thanks.

[superdave]

I am at 4800' and with my 450 with a HMF and cam mod and no lid with a K/N filter I was at a 48 pilot and a 168 main with a GYTR needle in the middle....Ran great....D

[bigboybanshee]

You are right for thinking it's a lean condition, mine did the same thing before I got it jetted right. It's also not uncommon for it to shoot a small flame out the exhaust, but it shouldn't be doing it consistently.

 

What kind of wrench does he need for the plug? Last time I changed it we didn't use a wrench, just a ratchet with the right sized socket/extension.

 

Granted, I'm at sea level but I have the same mods as superdave (different pipe though) and am running a 172 main, 48 pilot, NCVQ needle at the 4th clip from the blunt end...fuel screw is 2.5 turns out....just for reference