Carb? Ignition? ??? HELP

Well I have a problem that is driving me crazy. I have a 1977 MGB and it will not idle or rev up. If you try to rev the engine it back fires and pops and cracks then will not idle. However if you pull the choke it will atempt to idle but the engine looks like it is going to jump out from under the hood. The engine has a Zenith carb with a manual choke and I have check the ignition and all is correct. Also when adjusting on the carb it never changes the sound of the engine unless you adjust the idle that does effect the sound and it will hold a very high idle. I am at the end of my rope on this thing. Please lend me some help on what this could be. One other thing, I have checked for vacume leaks and can not find anytihng and the fuel preasure seems ok. One other strange thing with the choke fully out the car seems to run ok for a short whle and then it all starts again. Please help.

Thanks in advance
JM

JM, Check the carburetor diaphragm. If it is split or leaking it can cause the problems you describe. A new diaphragm costs $5-$6.

Clifton

JIM DID YOU FIND OUT WHAT YOUR PROBLEM WAS AS MY MG SEEMS TO BE SUFFERING THE SAME , BACKFIRING ON ACCELERATION, IDLE SPEED WILL ONLY MAINTAIN IF KEPT HIGH 5,000 REVS. aNY IDEAS? MALL

Clifton is right - it's probably a split diaphragm. If it is, after you replace it (be sure you put the small locating tits in the correct slots on the piston and carb body), then remove the plugs and clean them. They are probably fouled. You may even want to replace the plugs if this has been going on a while.

Let us know what you find.

John