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Dirt Bike Discussions By Brand
Canadian Daves JustKDX
Plug Chop Pix
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[QUOTE="Rich Rohrich, post: 681999, member: 16241"] It's not that the half throttle plug reading method is necessarily wrong it's more a case of understanding it's inherent shortcomings. The basic problem comes from the characteristics of the needle at half throttle.You are into the needle's taper at this point. When you are trying to do back to back comparison tests it's obviously important to control as many variables as possible. Even small variances in throttle position near half throttle will have a dramatic effect on the plug reading. The point is you need a positive method to determine the [b]exact[/b] point of half throttle (like a TPS reading). Without that you will have a difficult time determining if a change in the plug reading has been caused by a change you made to the needle setting or if it's from a difference in the throttle position when the reading was taken. The same problems generally hold true when trying to read the 3/4 open position. I mean absolutely no disrespect to Canadian Dave by any of this. He wrote a couple of [b]outstanding[/b] tutorials on carb jetting and needle selection. I just know from my experience that a mark on the throttle housing is totally inadequate if your goal is to compare spark plug readings generated by the half-throttle (or any other position) fuel flow. Determining the correct mid-throttle jetting ultimately gets down finding a useable fuel curve as the throttle [b]transitions[/b] from 1/4 to 3/4 . On the other hand, marking the throttle at various positions for use with the [i]ride and feel[/i] method is an excellent approach and will pay huge divedends in terms of speeding up the process and improving your accuracy if you compare throttle positions to a needle chart like Dave provided. Even better would be to purchase the JD jetting program and really do it right. In the end as long as you get the performance you are looking for, how you get there isn't really important. ;) [/QUOTE]
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Dirt Bike Discussions By Brand
Canadian Daves JustKDX
Plug Chop Pix
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