The original 12mm Keihin PA carburetor on the NC50 (shown on right), really was problematic for me. The pressed in main jet really limits any easy tuning. The carb didn't respond well to temperature and density changes, so much so that I zip tied a small screwdriver to the NC50 so I can readjust it on days that it didn't want to idle well.
I moved onto the Dellorto SHA 15.15, middle. It does have replaceable main jets and has been much better. The idle air/fuel mixture, you have to adjust by replacing slides, which is unique to my experience. Treatland, http://treatland.tv, has an adapter that will let you bolt this carb directly to the NC50 stock intake. This makes it a very easy swap. The large 60mm air horn on the carb limits the choices in air filters, but again, Treatland has some options and I am using a Mallosi air filter from their site.
I have purchased a Mikuni 20mm VM round slide carb and a Weak Ends intake to use with it. Again, both from Treatland. My suspicion is that I will like this carb since it is similar to many of the Motocross VM carbs that I worked on in the 80s and 90s. The Mikuni has a 43mm air horn.
Right now, I running about 10,000 rpm at 38.6 mph. If we use the Jennings formulas for carb sizing, and the K-Star 44mm cylinder I am using, safe carb bore size comes out 19.6mm.
nice
ReplyDeleteHi I'm setting up a very similar nc50 to yours with an Athena kit and vm20. What jetting size did you settle on for the Mikuni? On another note did you notice the massive size difference in depth of the side transfer ports compared to the casing. Did you have any issues with leaks around the gaskets here? Did you adapt your case port in any way.... there's not a lot of meat to work with there!
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