Attention SU gurus! I have a question about SU carbs, since I am so used to
Mikuni/Weber/SKs and have not worked on SU's in quite a while. These are on a
friend's 1600 race car. Carbs were allegedly rebuilt (but we question the
quality of that rebuild). Here is the deal: I get best idle with the fuel
adjustment all the way in tight... no black smoke, carbs respond as they should
when each plunger is pushed up to check the functioning of the other carb. Car
runs great until about 5200 rpms, then power drops way off and the car starves
for fuel (car stumbles, plugs show lean). If I richen the mix considerably, I
can get the rpms to climb to nearly 6000, but then she is way too rich on the
bottom end. I surmised that we had a float level problem, so I openned them up
and adjusted the needle arm so that they turn off flow earlier to lower the
level in the bowl. I seem to be moving in the right direction now, as I am
able to richen the mix at lower rpms without being too rich and so as to have
it rev to nearly 6000 rpms without choking (but it still is, just later). I
ran out of time to do a lot of playing with it, but I wanted to know if others
with more experience with SUs feel that I am going in the right direction.
Also, do the earlier (N-17?) SU needles run a bit fatter at the top end? I
have a set of older carbs that probably have good needles in them that I could
try if that is the case. Greatly appreciate your help!
Greg Burrows
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