CV Carb Needles Dyno Test

 

The needles used in CV carburetors are always a source of questions. People often try to draw conclusions from measuring the needle diameters at various points, but the problem with that is that the needles are often different lengths, and that can skew results in a direction not indicated by the shank diameter.

 

Anyway, I've done some limited dyno testing in search of an answer and I'd like to share the results. I went with two popular needles used in late model carbs as well as the 27094-88 needle (N65C) from the 1988 Sportster, which is a very popular needle in the performance community.

 

 

 

The results had a fair amount of variation, I did my best to pick a result for each needle that was representative of the average result.

All of these results were taken with the same main jet, and within a very short period of time between each other.

The test bike was a bone stock 1999 Buell M2. Stock CV carb (some jetting tweaks is all), engine internals are all stock, stock muffler, stock ignition module, coil, plug wires, and 10R12 plugs. The carb slide hole had not been drilled and it's using the stock slide spring. The testing was performed without an air cleaner in place to save time.

Notice that the carb always goes lean when the throttle is first opened, then fattens up as the rpm's come up, eventually ending up too fat, then it comes back a bit.

Changing the main jet (which I did a bunch of) basically moves the whole line up or down without really changing it's shape.

My general impression is that the needles aren't terribly far apart. However, the NOKK line is enough flatter than the others that it's probably the needle I would recommend. I particularly like how it richens up faster than the others.

 

 

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