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Necj vs JD blue vs JD red


cmarico
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Cmarico, to explain the differences/similarities properly would take a bit of time.  It’s not just a one sentence answer/explanation, plus we don’t know your jetting knowledge.  
The JD needles are a tried and proven alternative to OEM needles in both Keihin and Mikuni carbs (different shape needles though for each brand so you can’t interchange) and the NEC or RM Suzuki needles are for Keihin carbs only.  
Over on KTMtalk forum in the USA there is a current thread in the jetting forum that Is discussing exactly what you ask for and some of the jetting gurus are posting up good info.   I suggest you have a look and read.   

Then jet your carby and come ride with us carby blokes 

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If you know how to measure taper and understand how the taper effect the mixture at the precise throttle openings, plus the diameter and length, then you can figure out JD's blue or red needles against Keihin needle chart ...but it could be a straight, dual taper or triple taper (majority of needles in bikes). Then measure the clip spacings...you'll often hear speak of half a clip leaner or richer that's the clip spacings urgh!!

Just like JD's are proprietary needles, so are Kawasaki (from memory they are the NAXX) and Suzuki (NEXX), in fact any manufacturer will create their own proprietary needle profiles to suit their engines which Keihin creates for them but won't list....l use to have a great kawasaki KR1S service manual that actually illustrated the a triple taper section from 0-3 and their diameter(s) of their needles which you can calculate which needle you are wanting..unbelievable how complex fashioning a needle is!!

Anyway, a needle is only one part of the carby tuning and l don't know your knowledge level of carbs so I found a web version of document that l've always go to when l use to get confused when playing with keihin carbs and trying to understand what effects what etc. And on the plus side, there are plenty of folks here that can help you out esp with a KTM300...hope it helps!!

https://static1.squarespace.com/static/5be4d5b35ffd2095efa9bdff/t/5bf1a09b6d2a7391b5a84730/1542561947962/KeihinCarbJetting-2015.pdf

PS. I'm on a TPI these days and all this is starting to be a distant memory/headache but great reminiscing 😉

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10 hours ago, ohmygewd said:

I found a web version of document that l've always go to when l use to get confused when playing with keihin carbs and trying to understand what effects what etc.

Great read, thanks for sharing. One point I haven't quite understood yet is when they refer to "engine idling at highest rpm" when adjusting airscrew. The highest rpm bit throws me.. How does one know when it's at its highest? 

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Great read, thanks for sharing. One point I haven't quite understood yet is when they refer to "engine idling at highest rpm" when adjusting airscrew. The highest rpm bit throws me.. How does one know when it's at its highest? 

That's the point where you've turned the air screw that little bit more the rpms begin to lower, it's very distinct and the motor must be warmed up....you shouldn't be blipping the throttle at this point as you should have a steady idle?

 

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1 hour ago, ohmygewd said:

That's the point where you've turned the air screw that little bit more the rpms begin to lower, it's very distinct and the motor must be warmed up....you shouldn't be blipping the throttle at this point as you should have a steady idle?

 

Awesome, thank you. When I read "engine at highest rpm", I imagine a bike screaming at redline. 🤪

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42 minutes ago, maccastrewth said:

Awesome, thank you. When I read "engine at highest rpm", I imagine a bike screaming at redline. 🤪

No...that's when you send it and the throttle is whacked open against a log😂😬.

Trailtech make a good hour meter/tech, even the ebay specials,  which is much easier for setting and settling on the right idle rpm (around 1400-1450 on tpi and Beta says 1700-1800rpm but l settled at 1500rpm) or one of those engine analyzer that looks like a multimeter are probably more accurate but you can't really carry that around.

Oh...google notes, write or note everything down even the temperature of the day and where you've ridden, MJ size, PJ size, clip height, needle type, AS turns and more importantly, how the bike felt at the time - nothing worst than playing with jetting and relying on memory.

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20 hours ago, ohmygewd said:

If you know how to measure taper and understand how the taper effect the mixture at the precise throttle openings, plus the diameter and length, then you can figure out JD's blue or red needles against Keihin needle chart ...but it could be a straight, dual taper or triple taper (majority of needles in bikes). Then measure the clip spacings...you'll often hear speak of half a clip leaner or richer that's the clip spacings urgh!!

Just like JD's are proprietary needles, so are Kawasaki (from memory they are the NAXX) and Suzuki (NEXX), in fact any manufacturer will create their own proprietary needle profiles to suit their engines which Keihin creates for them but won't list....l use to have a great kawasaki KR1S service manual that actually illustrated the a triple taper section from 0-3 and their diameter(s) of their needles which you can calculate which needle you are wanting..unbelievable how complex fashioning a needle is!!

Anyway, a needle is only one part of the carby tuning and l don't know your knowledge level of carbs so I found a web version of document that l've always go to when l use to get confused when playing with keihin carbs and trying to understand what effects what etc. And on the plus side, there are plenty of folks here that can help you out esp with a KTM300...hope it helps!!

https://static1.squarespace.com/static/5be4d5b35ffd2095efa9bdff/t/5bf1a09b6d2a7391b5a84730/1542561947962/KeihinCarbJetting-2015.pdf

PS. I'm on a TPI these days and all this is starting to be a distant memory/headache but great reminiscing 😉

Spot on. Measurements / specs are the go. Many years ago "expert" tuners were telling me to run a needle with a different part number from a different make of bike for my KX. I was happy with what i had but out of curiosity i checked out the specs to see how it would change the throttle openings / fuelling; it was exactly the same needle dimensionally as mine.

Type of riding and rider style also effects needle selection. Eg the extra tapers help for aggressive / big off and on the throttle and a lot of hard / quick full throttle acceleration like MX and high speed higher throttle opening use under heavy loads like desert compared to trail riding with a lot of lower to mid throttle openings and light loads at higher speed sections.

 

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