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Baseline carb settings 08 wr450f

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Hi,

 

this is bike has apparently been tuned for the mods it has and it runs pretty good, to be fair. But, it's sooting up the rear blinker pretty fast and likes to fart and pop a bit on decel, as well under light/medium acceleration, towards the top 1/3 of the rev range.

 

the bike has all the free mods done, plus a fmf pipe and pc4 muffler(no baffle), powerbowl 2 installed, and I use 98 RON fuel.

i ride at 250-1200ft/80-400m altitude. Temps vary from 50-90/10-30c around my area.

 

thanks for any suggested baseline settings.

Edited by simonr23

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165m

45p

NCVS needle on 3rd

Disabled ACV

^^100 pilot air jet ^^

Disabled EGR

R&D fuel screw (you probably got that with the PB kit)

Set fuel screw with a hot motor that has the lowest idle possible, for the highest idle using the fuel screw only.

 

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Thanks Krannie. I don't understand your last sentence about the fuel screw/idle speed. Do you mean once the motor is warmed up, turn the fuel screw in until the engine only just idles? Or, have I totally missed the point there.

 

 

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1 hour ago, simonr23 said:

Thanks Krannie. I don't understand your last sentence about the fuel screw/idle speed. Do you mean once the motor is warmed up, turn the fuel screw in until the engine only just idles? Or, have I totally missed the point there.

 

 

Hot motor. Kill it. Put the fuel screw at 1 turn out. Start it. Lower the idle as low as it will go. Now raise the idle using the FUEL SCREW. If it goes too high, adjust the idle screw. Fine tune it for the smoothest highest idle. It is very subtle, so pay attention. 

If you start with a 'normal' idle, you will be compensating for the high slide, and it will be both rich and lean depending on the rpm.

This should be about 1.5 turns out from a soft all the way in. This is ideal. You will need to fine tune it every time the air density changes dramatically.

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Excellent, thankyou.

so the fuel screw(this is the one on the extension tube from the r&d bowl, near the 'choke'?) is set to one turn out from a gentle closed position(hot motor) as a baseline.

from here slowly turn the same screw in until it is only just idling.

now raise the idle a bit- using the same screw, until it is idling smoothly, but still not too high. 

Im not sure why the idle might go too high, but I'll do a bit of googling about carbies to improve my knowledge. If it does go too high though, I now slightly turn in the idle screw, to bring the idle back down a bit.

 

have I got myself in the ballpark of understanding now? 

 

Mechanically im somewhat competent, but I've not dealt with carbies before, except on r/c 1:8 scale buggies.

They only had a idle screw, low speed needle and a high speed needle. I never had to change parts, just make screwdriver adjustments.

I'm hoping that I'll be able to relate these new terms against my existing vocabulary.

 

thanks again.

Edited by simonr23

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Also, can I buy these sized jets/needles from my local Yamaha dealer, for quick turnaround? I'm in Australia, so it'd suck having to wait two weeks before I can do this work.

 

thanks.

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Ok, cheers. Should the first 'fuel screw' actually be 'idle screw' in your post above?

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16 minutes ago, simonr23 said:

Ok, cheers. Should the first 'fuel screw' actually be 'idle screw' in your post above?

Hot motor. Kill it. Put the fuel screw at 1 turn out. Start it. Lower the idle USING THE IDLE SCREW as low as it will go. Now raise the idle using the FUEL SCREW. If it goes too high, adjust it back down using the IDLE SCREW.  Start over if necessary. Fine tune it for the smoothest highest idle. It is very subtle, so pay attention.  The end result is you getting the idle turned up using the fuel screw, to the idle speed you need/want.  Then you never touch the idle screw again, only the fuel screw. 

Whether it's a two stroke (air screw) or four stroke (fuel screw) this is the method for setting the 'pilot circuit trim' for the pilot jet, combined with the height of the slide, and the pilot air jet size.  All motorcycle carbs tune this way. 

Edited by Krannie McKranface
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Had the bike at the dealer. They said it's set well. 

 

Tonight i I gave it a service and the plug was really sooty. The manual says that could be from low rev running. True? I replaced the plug anyway. It was only 600kms old. Suburban riding for 80%.

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The sooty-ness could be caused by a number of things. The most common would be crappy gas. Next would be low rpm riding. .....it can also be from valve stem seals or rings that are letting oil get past.  A leak down test would confirm this.

I would not worry about it. 

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