Needle configuration

[canyncarvr]

Given: L1 is NOT the length of the straight section of a needle, but the length TO the spot on the needle the diameter is 2.515, so there is likely some taper involved in the L1 measurement.

So, the larger the L1 diameter, the sooner the taper has to start on the needle to get to 2.515 on needles of the same L1???

Akin to º of taper. Other specs the same, a 'B' (1.25º) needle's taper starts sooner than a 'C' (1.5º) because the slope is 'slower'.

Putting three needles into JD's spreadsheet though, CEJ-CEK-CEL shows only what you'd expect from different diameters, namely the bigger the leaner. Maybe the spreadsheet doesn't take into account the angle start difference between different diameters? Maybe it doesn't make that much a difference? At some point, a larger diameter should cause a RICHER bottom due to the sooner starting taper º ?? Or the two offset each other?

Enlightenment appreciated.

 

[BRush]

I had a look at JD's spreadsheet and it seems to take the tapered portion of L1 into account. It calculates an "LT" dimension, which appears to be length of just the straight section and uses LT to determine where the taper actually starts. The formula for a single taper needle:

LT = L1 - (Dia - 2.515) / TAN(PI / 180 * Taper)

and the formulas for determining needle diameter relative to throttle position look like they are taking all that into account.

 

[canyncarvr]

Thanks for looking, BRush.

I just looked at the spreadsheet pictures!!

I know there are equations listed somewhere in an XL sheet, but even if I found 'em, I don't know that I'd understand what they were telling me.

Which still doesn't give me a sense for 'rule of thumb'.

ie: A BEL-1 is two clips richer than a CEL-3

A 'rule of thumb' derived from the above gives you an idea how to change angles, and know how close you are to the same overall fuel delivery.

Quite an amazing device, the carby!

 

[BRush]

I’ve noticed sometimes that the chart that shows the relative richness or leanness of one needle against another does not match up to my own sense of what it “should be” in the 1/8 to ¼ throttle range. But this stuff confuses me so most likely it’s my own mental map that is off. Some slow winter day, I was planning to trace it down to see where what formulas the graph is using for the plot data, just to satisfy my own curiosity.

 

[canyncarvr]

If it ever is (satisfied), I'd like to hear about it.

Thanks for your consideration of the 'issue'. ;)

 

[fishhead]

The taper does run out higher on the larger diameter needles but remember the dif is .1 mm per step or aprox .004 or .002 per side so it doesn't show up very well as it is a very small increment. The 1/4 degree dif between the c and b tapers shows up better because the slope is very slight to begin with. I'll ask my trig student to calc the difference and let you know.