Rich, I saw in the tech section under carburetors that your now having to work with Zamas that aren't 'twin jet'. Bugger, those were easy to mod, hopefully you will get your head around the newer type carbs.
Here's something I've run into when modding the 460 carb. I like the 460 carb because it has the largest venturi of the HD series (17.45mm) plus an offset main discharge nozzle - I think it will flow the best of that range of carbs.
The 460 carb is an EPA carb. I had originally thought that the small jet in the carb was a restriction on the low speed circuit - it isn't. Turns out it is an 'auxilliary' jet like on the twin jet Zamas. Unfortunately, it sits too close to the throttle plate and can cause problems with the idle, especially when it gets drilled larger (I don't know what the max size should be...)
Then I thought "where in the Hell is the source of fuel for the low speed circuit??" - I found it, I had to punch out the main discharge nozzle. You wouldn't believe it, the low speed circuit takes it fuel from the high speed circuit. There is a passage way drilled into the nozzle tunnel that leads to the low speed circuit.
I plugged the passage in the nozzle tunnel with some GB Weld, put the nozzle back in and then drilled a 1mm hole in the wetside just in front of the low speed needle seat in order to feed fuel to the needle. It completely changed the way the carb worked, it went pig rich immediately.
Not only is the idle more stable, but the max RPM is more stable. I'm going to do some more work with the metering springs, but I think I'm on the home stretch with this carb.
I thought you might like the information about where the low speed circuit picks up it's fuel as you may run into the same configuration in other carbs.
