06 yz450 Spark Plug burning white after 48pilot/170main

24 replies to this topic
  • KTMKarl

Posted April 06, 2006 - 09:12 AM


Wide bands aren't cheap or all that easy to install/use and ecspecially tricky without the aid of a dyno or some way to load the engine while stationary. You can get off base pretty easily with all the equipment in the world at your disposal, knowledge and experience makes the difference.

PS: another vote for leaving the plug alone with the exception of leaded race fuel or methanol (i'm wasting my time with methanol I never have figured out how to read that stuff! LOL) your wasting time trying to read plugs with pump gas or most no-leads. If your on pump gas and the plug is tan your bike is so rediculously FAT it shouldn't be able to pull a sick whore off a toilet. I plugged an air filter at the MX track a few weeks back and my bike was a little fat anyway, just for kicks I pulled the plug and low and behold she was bleach white! I'm talking about a bike that wouldn't hardly pull third gear to the limiter! Thats a fat mixture.

  • SureBlue

Posted April 06, 2006 - 09:28 AM


I put in an iridium plug today, and here's the original, white as white can be
Posted Image
And my bike has run perfect. So once again burned was right, you can't tell much from the plug.

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  • SureBlue

Posted April 06, 2006 - 10:32 AM


Actually this is not entirely true. Lets say you adjust the fuel screw richer the overlap causes the mixture throughout the rpm range to be richer not just at idle. The orifice size is increased allowing more fuel at all throttle openings. Adjusting more than one parameter at a time is a headache without a lot of experience. All circuits affect each other.

To my knowledge the fuel screw finetuning only affects jetting from idle to 1/4 throttle, not thru the whole range.
Pilot jet sets the basic jetting up to around 1/4 throttle, the needle from 1/8 to 3/4 and the main jet from 3/4 to WOT.
This is why I find it strange that so many neglect the needle, which is an important factor in jetting. Nobody rides at idle or wide open only, right?

  • Eddie Sisneros

Posted April 06, 2006 - 12:22 PM



you weld a bung in the head pipe.

these work fine with out a dyno.

they have inputs for tps and rpm.you record the data.then down load to your computer and watch it.you can see exactly what the jetting is doing at specific throttle input and rpm.

i have one on my ford lightning is well.

they are not real cheap,but not terrible if your really into to jetting.

  • SurvivorMan

Posted April 07, 2006 - 09:31 PM


Yeah, the wideband meter is out of the question. Shouldn't dealerships have this?
I went for a ride tonight and damn, the bike is running perfect!! I can't get it to pop on decel, nor will it hesitate down low. No grog or burbling, just clean crisp power. Even wide open down a road section it is clean....starts easy too,.

I use premium pump fuel
48 pilot, 2 1/2 turns out fuel screw
175 main
1 clip position richer stock needle (position5)
exhaust and airbox are stock
4000 - 5000 ft elevation, 12 degrees celcius.
No more lookin at the plug!!

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