I finally got my webberized brumby rejetted at a carb shop. Now it does not diesel (run on), hesitate from down low, doesnot ping in 2nd and 3rd at 4200rpm and can idle alright when its warm. There is just one thing about it, at idle every so often after 20-30 seconds I think it misfires, the tach drops about 50rpm and makes this bassy thud sound, (not metal on metal), thats the only way I can descibe it. Also the body of the car moves a bit but only for a moment while it hapens. If I rev it up to 1000rmp it doesnot do it. Has the problem got to do with ignition or fuel or am I being too vague? The mech also advanced the timing.

I really think that there is a problem with the ignition. the only problem the carb can have is if it runs out of fuel. Then it would conk out. So probably the problem is bad plug wires. The plug wires on a Sube are so long, there is more of a chance for faulty wires. Test them out. Nothing over 10,000 ohms.