182 Main in a stock YZ450F?

[cmcdaniel]

All,
I am new to this forum, thanks for having me. I have a stone stock 2006 YZ450F and when I bought it new last year it popped really bad on the decelleration, so I upped the main to a 175, then it was still popping but not quite as bad. I was running my fuel screw so far out that it actually fell out one day, so I figured up in the Main again and of course get a new fuel screw. So then I ran a 180 with the fuel screw at 1.75 turns out and it runs really good. I have talked to Jody Weisel (of MXA fame) and he talked to Doug Dubach and they are saying they run a 160 main in their YZ450Fs there is no way that I should be running that big of jet. Now, of course I get one email responses from these guys, hence why I am here. I only ride in the Ellsinore area in case you were wondering. Can any one tell me how my bike even runs with this big of a main jet in it? Would it be possible to have a huge intake air leak? It seems like there should be fuel pouring out of my muffler can doesn't it?

 

[biglou]

You need to up your pilot jet, not the main. An air/exhaust leak is a possibility also.

 

[Matt90GT]

Yup. You are upping the wrong jet.

increase the pilot to a 48 in the 450s. Then drop the main down to a 170.

 

[SFO]

keep us posted until you get it running the way you like.
There is also the pilot air jet but likr biglou said make sure you don't have an exhaust sealing issue or an intake manifold leak.

 

[cmcdaniel]

Guys, I guess I should have clarified, my bike runs fine, it runs like it should...I think. I have also owned every 4 stroke Yamaha has made since 1998 so I am used to their machines. The only thing I have not done, which will tell the ultimate story is pull the plug. This all came about when I was reading the latest test on the 2007 YZ450F in the March issue of MXA. They recommended a 160 main, which is what got my attention. Here is what they suggested.

Main: 160
Pilot: 45
Needle: NFLR
Clip position: Fourth from top
Fuel screw: 2-1/8 turns

 

[cmcdaniel]

See my last reply:

Guys, I guess I should have clarified, my bike runs fine, it runs like it should...I think. I have also owned every 4 stroke Yamaha has made since 1998 so I am used to their machines. The only thing I have not done, which will tell the ultimate story is pull the plug. This all came about when I was reading the latest test on the 2007 YZ450F in the March issue of MXA. They recommended a 160 main, which is what got my attention. Here is what they suggested.

Main: 160
Pilot: 45
Needle: NFLR
Clip position: Fourth from top
Fuel screw: 2-1/8 turns

 

[oldguy]

A broad stroke recomendation often will not work because of riding location and weather differances. My son's 06 YZ450f will backfire on deceleration whenever the temp drops below 60 degrees but 1/3 turn of the fuel screw is usually all that is needed to remedy it. He is running stock jetting on 93 octane gas