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Minor Problems with New 450F - Jetting, Electrical? Can you help?


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I picked up my new 450f yesterday. Took it home and rode around my rural neighborhood to break it in gently. The bike starts and idles fine. The problem is at 1/4 - 3/4 throttle where the bike surges and slightly sputters when the throttle is held in a constant position. This clears up when acceleration is increased. I have made no adjustments. Does this sound like a fuel screw or needle clip position problem? Any other ideas? Should I simply let the dealer worry about it? Also, it was 99 degrees and high humidity when I was testing the bike (these conditions made me wonder if the needle clip needed to moved to lean it out a bit). Thanks in advance.

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It could be several things but it is very likely not the fuel screw. The FS only affects the mixture when the needle is blocking the main jet (closed throttle).

Surging is usually a lean condition, but sputtering would be rich. You are describing both! Anyway, I would try moving the needle clip one notch leaner (move it up on the needle).

Don't turn to the dealer yet. Learn to jet your carb. It is very simple. If adjusting the needle clip position doesn't help, adjust it the other way. If one clip position either way doesn't help then it is something else.

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Thanks for the response and sorry for the confusion - I think "sputtering" describes the condition better than "surging" and thus a rich condition. Jetting is one of those issues that I have promised myself I would learn - there is no time like the present. I will move the clip up a notch tonight and see what happens. I agree with your thoughts on the fuel screw (not based on experience, just my limited understanding based on reading). Do you think it is safe to rule out electrical problems, or is it too early to tell? Thanks again.

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Do you think it is safe to rule out electrical problems, or is it too early to tell? Thanks again.

Bassr - it's too early to tell. Start with jetting, then go from there. ๐Ÿ™‚

Remember that your jetting runs should be with a fully warmed up bike...

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Jetting is one of those issues that I have promised myself I would learn - there is no time like the present.

Once you understand how the carb regulates air and fuel, you will be an expert - almost! ๐Ÿ™‚

(1) When you twist the throttle, it pulls up the slide so air is allowed to come in.

(2) The needle is connected to the slide, so the needle moves up at the same time.

(3) The end of the needle goes into the main jet orifice.

(4) When the throttle is closed, the slide and needle are down, and the pilot jet acts as a bypass circuit. The FS is just a fine tune to the PJ.

(5) When you start to open the throttle, fuel is allowed to pass through the main jet and the taper and position of the needle determine the amount of fuel coming through.

(6) After about 3/4 throttle, the needle is all the way up out of the way of the main jet, so the size of the main jet orifice is the only thing that regulates the amount of fuel coming in.

(7) The accelerator pump is useful for the transition between the FS/PJ regulating the fuel, and the needle/MJ regulating the fuel. The timing and length of the AP spray can create or resolve lean/rich conditions at this transition. As you have seen on this board, it can have a HUGE affect off-idle.

So there you go - FCR carb in a nutshell.

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Jetting is one of those issues that I have promised myself I would learn - there is no time like the present.

Once you understand how the carb regulates air and fuel, you will be an expert - almost! ๐Ÿ™‚

(1) When you twist the throttle, it pulls up the slide so air is allowed to come in.

(2) The needle is connected to the slide, so the needle moves up at the same time.

(3) The end of the needle goes into the main jet orifice.

(4) When the throttle is closed, the slide and needle are down, and the pilot jet acts as a bypass circuit. The FS is just a fine tune to the PJ.

(5) When you start to open the throttle, fuel is allowed to pass through the main jet and the taper and position of the needle determine the amount of fuel coming through.

(6) After about 3/4 throttle, the needle is all the way up out of the way of the main jet, so the size of the main jet orifice is the only thing that regulates the amount of fuel coming in.

(7) The accelerator pump is useful for the transition between the FS/PJ regulating the fuel, and the needle/MJ regulating the fuel. The timing and length of the AP spray can create or resolve lean/rich conditions at this transition. As you have seen on this board, it can have a HUGE affect off-idle.

So there you go - FCR carb in a nutshell.

Very well put!! I have been fooling with jetting for few years now, and have gotten the hang of it somewhat. It never hurts though to hear it explained other ways, and your explanation was very easy to understand for someone who is very new to it and for folks who have done it a bit. Kind of like one of those "good" teachers you had back in school, who just had a knack for making things easy. Thanks a bunch!

fofiveoh

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The FS only affects the mixture when the needle is blocking the main jet (closed throttle).

This is not totally correct. True the further you open the throttle the less the fuel screw has an effect; however the fuel screw does have a considerable effect on throttle openings 1/4 and below. Check the back of your manual, there is a great graphic back there describing which parts of the carb affect which throttle openings.

Personally I would first clean the carb, then if you're in 99 degree heat at sea level I would not be surprised if you needed to lean the fuel screw and/or needle a notch or two as compared to the stock setting.

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The FS only affects the mixture when the needle is blocking the main jet (closed throttle).

This is not totally correct.

Well, you're right that it is not not COMPLETELY correct. But it makes it easy to understand. The fact is that although it is a bypass circuit, it is not totally shut off as soon as you open the throttle. So the mixture is affected by it, until the the mixture provided by the main jet/needle taper/position overwhelm it.

The point is to UNDERSTAND how it works at it's most basic level. Then the nuances can also be understood. ๐Ÿ™‚

fofiveoh - thanks for the vote of confidence!

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My 450 did the same thing (sea level) I would put some time on it before changing any jetting (2 tanks) after the rings

seat things will be a little different. I moved the clip from the forth knotch to the second....worked for me,but

your the one riding the bike so you will have to play with

the jetting..stock pipe and the jetting is pretty close

after the needle was leaned out,fuel screw 2 1/2 turns out.

BC ๐Ÿ™‚

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I think the problem is solved. I ended up raising the clip two notches (lowering the needle) to the second notch from the top, which leaned the bike out and cleared up the sputtering. I may still need to go to a 40 pilot jet (42 standard) because I am only out about 1/2 turn out on the fuel screw right now. The exhaust note is currently very crisp and there is no bog or hesitation off-idle (on the stand). I will test it at the track this Sunday afternoon. Thanks for all the advice.

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