Hi, I’m having a confusing time with tuning a bike specifying the needle reqd. Apart from the OEM Bike Manufacturers number & Sudco number the std Keihin numbering system seems fairly straight forward. Although more used to Mikuni stuff, all the Keihins I've used have been ok on needle so never had to worry much more than a taper or pos change.
Or so I thought.
The std number system is something like
DEK
The first being the taper, 2nd length where starts & 3rd being diameter.
Diameter being the most important to get right.
So some background. I am building a roadbike but with a Trinity Cheetah 496cc kit for a banshee (RZ350). I have new 35mm PWKs.
But it is very rich. I set the mains up on the dyno & the pilots until it would idle, but the needles are just too thin. My GasGas uses a PWK & the LTR jetting kit uses a thicker needle so you can control it better with the pilot cct from closed, ending up with bigger pilot jets & less large droplets being sucked through the needle. I'm down to 38 Pilots & that's pretty small.
OK so I need thicker needles so I go up a size with some OEM needles that are supposed to be leaner (thicker diameter according to conversion chart). No diff. Hmm, measure them & the DEK ones & they are both 2.68mm at the base diameter (closed throttle before taper starts).
So I order some BGNs (3 steps leaner & shallower taper on to of that). Still filthy rich. Measure those. 2.70mm. Hang on that’s virtually the same & a sight thinner than the chart says they should be. (N is supposed to be 2.725)
What’s going on? Aren’t these supposed to be thicker?