@devo I'm in your neighborhood, and I'm of the opinion that high altitude doesn't really change anything. Engine vacuum is lower or higher, based on altitude, but you do have to give it more throttle, either with the idle speed screw (there is a limit to how much) or with the gas pedal. It isn't like the carb meters out fuel-mix different up here, it just takes a greater volume of less dense air to consume the same amount of fuel from the bowl. Nothing changed for me going up to the ski hill.
@Fj80oregon I'd try out your existing carburetor. In my opinion, carb dip, a proper accelerator pump boot. and a rebuild kit is the way to go, depending on what you are starting with. Especially if you are keeping it kinda vintage, the original carburetor has more value, and it (mine is a 75) has a cast-iron base, so the primary throttle shaft will never wear out there. However, I might have picked up some mpg with the OEM/ new-Aisan version of the made-in-Japan model that you mention; it has smaller jetting, and a choice of smaller jets, and a smaller venturi (iirc), but, the mpg gain is probably because the motor was slowly getting congestion cleared-off of the top of the valves. I have a china carb that is real similar to the Aisan, and made-in-Japan ones, but, I'm afraid to try it out, as they used sealant between the air horn and bowl, so without (easily) being able to remove the fuel, I'd have gas turning into varnish if I shelved it after an afternoon of use; out-of-the box, it also needed tightening on one of the screws that holds the bowl to the carb base.
otherwise, if you are collecting parts...
- a Dorman "cable stop" 1/16-inch hole at local auto store for the stock choke cable-end
- a spacer for the stock air cleaner assembly (it sits lower than ERG-equipped carbs)
- a longer stud for air cleaner assembly plus the spacer (M6x1, iirc) - I cut one from a really long screw from the hardware store, and secured it with a new lock-washer and nut
- I employed flat washers and fresh lock-washers for the (M8, iirc) intake studs, not sure what the original hardware was. An extending magnetic pick-up helps when you drop hardware in the tight spots, and a stubby or crow's foot M12 or M13(generic hardware) wrench to get in between the carb and the valve cover
- A section of fuel line with a smooth (unthreaded) section of a screw secured with a hose-clamp becomes the plug on the tank-return line, so the grinder with a cut-off wheel is what I used (someone should try hacking-in the return line on one of these, drill and tap, the boss is there on the casting)
- You might need some caps for the emission lines? I have exhaust headers, so I didn't need to cap the EGR system.
A tachometer-type multimeter is how I got my 2F idle-speed at about 600 rpm, then adjust the idle mix until it runs smooth or slightly rich.
