The Main Jet with o-ring should be a snug fit; better to err on tight rather than loose, I have found. Having a tighter fit may make it a little more difficult to pull out the jets on the next rebuild, but hopefully you won't have to do that so often.
I have found that when you don't have a tight seal on the Main Jet o-ring, throttle response is compromised because there is an inaccurate amount of fuel/air mix via the emulsion tubes when the needles are raised. Having a loose fit allows an extra amount of air to mix with the fuel and that may create symptoms of a lean mixture.
But back to your overflowing issues. Recheck your float heights. According the webs, a '73 CB350F is 21mm. You'll need either the
float height tool (I've seen people get crafty making a guide out of old credit cards), or a set of
calipers with a depth gauge. There are a few methods to verify the heights: the clear tube method which is not fun and can get messy and time-consuming to fine tune floats by having to remove the bowls, or you can give the cool low-compressed air trick developed by Strynboen which involves hooking up your fuel line up to a compressor with an in-line regulator and using air as a substitute for fuel to gauge the fuel heights across your carbs.
According to Strynboen:
to adjust the floth height...the air escapes..until the valve get stuck of the flot...and the exatc point is clerly to be heard..and use your messure gerete you get a perfekt adjusting...vitaut any fuel vaste all over the shop....
It's a really clean and relatively accurate method to get your float heights measured evenly across the carbs.
When you're bending the tangs on the floats to adjust the heights, to measure the height, lean the carb rack back a bit to ease off some gravitational weight that the floats will have, in fact, I even rest the carbs on the intake side opposite the air filter intake (basically, tilting the whole carb rack 90° of its stock orientation), and then glide the float height gauge or caliper depth gauge across the mating surface of the float bowl against the surface of the top of the float and see how the bottom of the tang interacts with the float needle. Make sure that the float needles are fully seated. The tang should just gently caress the float needle. Keep doing this until you 21mm feels close. This is where the compressed air trick comes in handy. While the carb rack is in this 90° orientation, rubber bands can be used to keep the other floats down to make sure that the fuel, represented by air here, does not leak (or hiss out). You only need a small amount of air, so it helps to be in a quiet place while doing this so that you can hear the hiss of air leaking out as you measure the float heights. Simply move down the line as you feel comfortable with the float height adjustments.
I hope this makes sense. I was hoping tequila would help but maybe it did not.
