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DanielGalloway

Try this again...

5 posts in this topic

I posted this in the jetting forum under the heading "Correct me if I'm wrong", but I didn't get any responses. So I thought I'd give it a shot here.

One of my pet peeves is seeing someone ask a question that has been covered before, and having a "veteran" tell them to use the search function. To keep myself from being the newb that gets slapped on the hand, I've done quite a bit of research involving various functions of different jets in the WR's carb. Here is my earlier post...

Newbie here, I've got an '06 WR450F that has had nothing done to it but the YZ throttle stop modification. When I get time, I'm going to perform all the free mods and dial in the jetting, so I've been researching and learning all I can about jetting. During this time, I set up a table that I think will help me keep everything straight in my mind. I'd like you guys to look it over and tell me what I've got wrong so that I can correct it. It may even be useful for other newbies like me who haven't been taking these carbs apart forever. Here it is:

Component - Circuit - Adjustments - Range

Fuel Screw - Pilot Circuit - Out to Richen, In to Lean - Primarily Idle to 1/4 throttle, although it has some affect through the entire throttle range.

Pilot Jet - Pilot Circuit - Bigger Size to Richen, Smaller to Lean - Idle to 1/4 throttle

Needle - Needle circuit - Raise Needle (Lower needle clip) (Higher Number) to Richen, Lower Needle (Raise needle clip)(Smaller number) to Lean - 1/4 through 3/4 throttle

Main Jet - Main Circuit- Bigger Size to Richen, Smaller to Lean - 3/4 through Full throttle

Leak - Accelerator Pump Circuit-Bigger Size = Smaller, shorter Squirt, Smaller Size = Larger, longer Squirt. - Suddenly opened throttle from idle.

Starter - Starter Circuit- Bigger Size = More fuel to allow engine to idle when cold - Idle Only used when cold start knob (similar to choke) is out.

***The Fuel Screw takes the place of the Air Screw that was traditionally found on two stroke carbs. Most FCR owners benefit from an aftermarket easily adjustable Fuel Screw from MSR or Zip Ty.

***Four strokes lack the vaccum that 2 strokes do to properly "pull" fuel at idle speeds, thus the need for an AP circuit.

***Needles with narrow tapers are richer than needles with thicker tapers. Narrow=more fuel flow around the needle while Thick=more fuel blockage by the needle.(2)

References:

1. http://www.thumperfaq.com/fuel_screw.htm

2. http://hondanighthawks.net/carb14.htm

OK guys, there it is, rip it apart and tell me what I've got wrong...

Thanks in advance

Daniel

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Good job, most of the time I am happy when my bike starts. Take all of the advice and use what you want, ride to be happy. I have 5 friends with 450 WR's and we all have different set ups. Old guys are always cranky to the young guys, dont worry about it.

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One of my pet peeves is seeing someone ask a question that has been covered before, and having a "veteran" tell them to use the search function. Daniel

My only comment is Use The Search Function. Sorry I couldn't resist.

Good job Daniel. As a bit of a newb myself, I would find it valuable to learn what rich and lean feel like. In the manual it says things like "the bike breathes hard". What the heck does that mean.

Anyway, good job Daniel.

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Needle - Needle - Raise Needle Clip (Higher Number) to Richen, Lower Needle Clip(Smaller number) to Lean - 1/4 through 3/4 throttle.
Lowering the clip on the needle (higher number) will richen the mixture and vice versa. By lowering the clip you are raising the needle, allowing more of the taper to be exposed.
Leak - AP-Bigger Size = Shorter Squirt, Smaller Size = Longer Squirt. - Suddenly opened throttle from idle.
Correct. Only like to add that a smaller LJ also squirts a larger volume of fuel. Smaller is richer.
Starter - Starter - Bigger Size = More fuel to allow engine to idle when cold - Idle
Correct. Only like to add that the starter jet only has an effect when the choke is out.
***The Fuel Screw takes the place of the Pilot Air Jet that was traditionally found on two stroke carbs. Four strokes lack the vaccum that 2 strokes do to properly "pull" fuel at idle speeds, thus the need for a fuel screw.
The fuel screw takes place of the air screw on 2 strokes. They basically do the same thing, only one meters air and the other meters fuel. The fuel screw richens when turned out by adding more fuel. The air screw richens when turned in by reducing the amount of air.

The pilot air jet controls vacuum at the pilot jet. A larger PAJ will increase the vacuum at the PJ which will draw more fuel through it, making the jet too rich. To correct you would need to lean the PJ.

The 4 stroke vacuum issue is the reason for the AP circuit.

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bg,

Thanks for the reply, that's exactly what I was looking for. I'll edit the original post to correct this info, and highlight what I've changed so anyone else who looks here will know that it has been changed.

Thanks again,

Daniel

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