Jerry,
I just posted on this in the Jag forum (Fuel pouring out top port of carb..)
In my case the float hinge had popped off on one side, the side which contacts the button shut off on the grose jet....
This probably isn't the case it sounds in your situation, but the bottom line is the float is not contacting the jet to push it far enough up as fuel fills the bowl, allowing it to shut off the fuel intake for that carb. The excess is probably also pouring back into your intake into the exhaust. I would bend (adjust) the float to make less clearance distance, this is trial and error. The idea is to make sure the float rises high enough to close the jet. Start with a gradual change, see if possibly you have the factory procedure for your car which would give you a starting point. You probably aren't having the issue on the other carb, so you may measure both float to jet shut distances to see if this may be the case. A backfire with this issue is an engine fire in the making. Leave the air cleaner(s) off while you try to get the float level set properly. Also, I was able to cut down on the fuel pouring initially by adjusting that carb on the car, but of course, not a good fix, just trial and error and my trying to avoid pulling the carbs and checking the floats. Your jet may be bad, but sounds like an adjustment. To test that you could switch the jets, see if the same condition occurs in the other carb..... Hope this helps, and I don't think that Grose jets are too horrible, try the float level adjust before you scrap them. (Maybe swap the jet and float to the other carb, then see what happens... a quick start should tell you right away if you need to replace the jets and floats, test swapping just the jets first though. Also, have you loosened and calibrated the throttle shafts on the carbs? Just a thought, but all of these steps I did corrected the problem and tuned the carbs to work together.)
Brian /bcforum/images/%%GRAEMLIN_URL%%/cheers.gif