Aussie WR450F 2008 model carb question

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Guys,

(Just being lazy here) .....

What size is the stock pilot jet in the Australian release '08 WR450F?

I want to order a smaller one for my bike.

Cheers,

Greg

You can down load the owners manual for your bike free from the aussie yamaha web site in PDF file. If you dont have a owners manual.

you lazy prick! :banghead: stock = 45

but a lot of dealers put in the spare 50.

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LOL!

Thanks guys.

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Turns out mine had the 50 in it!

Why they fit such a large pilot jet is beyond me. I suspect this is part of the reason the thing chews so much fuel!

I fitted the 45 pilot I had, just to check and it's still too big. I need to turn the fuel screw all the way in to get any rise in idle revs.

Looks like the carb will be apart again and the 40 I bought will find a home inside it!

Hopefully this one will be the right size.

I've also fitted a smaller main jet, it has been rich since I bought it, I've gradually been going smaller with my jets, trying to get it right.

Greg

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Looks like the carb will be apart again and the 40 I bought will find a home inside it!

Hopefully this one will be the right size.

Greg

40 pilot seems a bit low but hey go for it . But thought that you might not know but loosen the carbie clamps, take the hot start out of the carb you are then able to spin the carb enough to gain access to the pilot jet,through the bowl plug, with a small screwdriver all of about 1/2 hour work

cheers

Im currently using a 45 but its still a bit rich with fuel screw about 1/2 turn out. Im going back to a 42. They stall heaps less and easier to restart with the smaller pilot jet. If you leave the air jet out like alot of Australian bikes are from new you can normally go up a size in pilot jet.

I recommend #48 or #50 with 1&1/2 fuel screw turn out and 4th crip #DTR needle.

If you leave the air jet out like a lot of Australian bikes are from new you can normally go up a size in pilot jet.

Aaah, ok. I didn't know this. (ie about the air jet). I didn't even look at this aspect when my carb was off the bike, just quickly whipped the pilot and main jets out and replaced them with the new ones.

Cheers,

Greg

Greg, Have a look in your spares kit and see if the Air Jet is in there? If the dealer fitted the 50 pilot, they might have fitted the Air Jet for you too?

I am interested in what main/needle settings you have ended up with?

Irrespective of what slow air jet you have or do not have, follow this:

Fuel Screw/Pilot Jet

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

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If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

This is exactly the case with my bike, hence the need to try the 40 pilot jet. The idle speed actually increases a little when the screw is right in.

Cheers,

Greg

A fairly well respected jetting guru on DBW posted this recently:

"The Keihin FCR carb runs a pilot bypass which means even with the fuel screw fully wound in, fuel runs through that circuit. It will also get fuel from the main jet passed the straight section of the needle."

So wouldnt this test not actually be accurate for Keihin FCR carbs? Or is it incorrect?

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Main jet: 160

Needle: "JD Jetting" Red needle, clip in centre position.

I am running:

Main Jet: 168

Needle: "JD Jetting" Red needle, clip in centre position.

My exhaust only has a PMB insert and has not been fully modified like yours yet. I am not sure that can explain the much smaller main jet your running?

What differance did you notice as you went smaller? I think i will give it a go.

A fairly well respected jetting guru on DBW posted this recently:

"The Keihin FCR carb runs a pilot bypass which means even with the fuel screw fully wound in, fuel runs through that circuit. It will also get fuel from the main jet passed the straight section of the needle."

So wouldnt this test not actually be accurate for Keihin FCR carbs? Or is it incorrect?

Correct on both points. This is why, if the pilot is a bit large, as you close the screw, suddenly the screw has zero effect as you get close to closing it and the bike will still idle with the screw closed. In fact, in some cases, the idle will improve when the screw is fully closed.

The 'bleed' effect of the needle straight diameter is minimal and is rarely a concern. Though it is true that once you have the pilot circuit setup, and the main, you go off to do the needle, once that is done, you should revisit both the pilot and main to ensure needle changes (not just clip position changes) have not affected them. I've found only when a radically different needle is tried does the main or pilot get affected.

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