Quote:

Quote:

You will have change something and get it out of tune, so you will have something to work out...



Well, there is still the air cut valve (ACV). My theory is that sometimes the ACV closes under acceleration & causes a temporary rich mixture; more preload or a stronger spring rate should mitigate that. See, I'm not done yet



Ryk, you don't know how true your comment was.

Here's what I've learned about the ACV so far:

A washer with a minimum ID of 8mm and a maximum OD of 14mm will fit in the ACV cap for ACV diaphram preload. I had 1 such washer on hand, 1.2mm thick.

The ACV diaphram coil spring is pretty stout. It measures 48.5mm OAL, .9mm wire diameter, 13.3mm outer diameter, 7 active coils, 9 coils total.

With the 1.2mm thick spacer, the decel AFR's went about a full point (a full whole number) leaner. Curiously, WOT was about half a point richer. I thought that was a fluke.

Next trial was to totally take the ACV vacuum channel out of the picture by removing the O ring and plugging the channel with a small custom-cut rubber "stopper" made from a rubber autobody panel insert. I also removed the spring shim, & left the diaphram & stock spring in.

With the ACV vacuum channel blocked off decel is about 2 full points leaner, & WOT is about 3/4 of a point richer. Somehow the ACV mods are also affecting WOT to a small degree. Not sure why just yet.

Light throttle acceleration response is sharper with the ACV full vacuum channel block mod, however at a cost of a bit more decel popping. It is not objectionable.

It looks like the mains will need to drop from 150's to 148's in order to compensate for the blocked ACV channel. I will order 148's & retest.

The ACV vacuum block mod is completely reversible by pulling the ACV cover, removing the rubber stopper, and replacing the O-ring (it's about 2mm thick & looks more like a grommet than a true O-ring).

Keep in mind the ACV cover is under spring pressure, so keep thumb pressure on it while removing/replacing the screws.

Some of the dual-sport thumper guys with CV carb/s mod the ACV so it cuts pilot air all the time, however I don't see any advantage to doing it that way.

I'm not sure yet if the OEM ACV configuration or the blocked vacuum channel will prove to be best, however I don't think I'll use the ACV spring preload washer again. All in or all out, & tune accordingly.

Now the wait for those K OEM 148 mains...

And some pics to follow when I get some time to post them.