This post won't be useful to anybody using a CB750 in a bike, but I'm posting it in case it's useful to someone using one in an application where it's exposed to lateral G. I use a CB750 in a vintage racing car (see my avatar), and I know there are people who use them in racing sidecars, where they also see lateral G. This post is about my solution to a problem I encountered where the fuel sloshes to the side of the float bowl durng a turn, and the engine starves out. I got some good advice on this forum and was able to work around the problem to some extent by playing with fuel pressure, float level, and jetting. But the ultimate solution was to create a sump in the float bowl and extend the main jet down into it. Here's how I did that.
The first photo is a shot of the end result, showing the brass sumps attached to all four float bowls. The subsequent photos show how the modification was fabricated. Each float bowl was modified by boring an 11.5 mm hole in the bottom, which was subsequently tapped with M12x0.5 thread. The brass sumps were turned from hex bar on the lathe and have a male M12x0.5 thread at the top. The bore of the sump is 10.5 mm, which is a big as I dared make it. There's an o ring around the base of the thread. Yes, I know that's not the right way to use an o ring, but it was the best I could come up with. There's also Loctite stud mount on the threads, partly to keep them from vibrating loose and partly for sealing.
Finally, the main jet is lowered by placing a male-female union between it and the carb body (final photo). The union is turned from 1/4" hex brass. (The one shown in the photo is a prototype that was made from aluminum.)
The sumps are designed to be exactly 10 mm deeper than the stock float bowl. If I were to do it again I would probably opt to go even deeper, maybe 15 or 20 mm. The 10 mm sumps work pretty well, but still lean out slightly in one turn at my local track.
