Zenith carburetor trouble Help!

I recently reassembled the catalytic converter on my 79 MGB and today put the carb back on. When I started the car, the engine revved up to about 2800 rpm and held there steadily. I figured the idle speed screw was out of adjustment, but fiddling around with it didn't change the rpm. This led me to believe either the piston or the valve was sticking, however after inspection this didn't seem to be the case.

After that, I couldn't figure out what might cause this. I tried leaning out the idle mixture, and this brought the rmp down to around 1000, but at this mixture the engine was jumping from 500 to 2000 back to 1000. My dad and I timed the engine a few months ago and the car was doing just fine.

I need to leave for college tomorrow or thursday at the latest, but I can dedicate all my time to fixing this problem up until then. If anyone could provide input as to how to fix this problem, it would be greatly appreciated.

Alex

Alex, I'm not an ZS expert but I do know a bad piston diaphragm can cause similar problems. Check it for condition, no splits, tears or stiffness. Replace if bad.

Clifton

Thanks Clifton. I'll check that out today.

Check the diaphram....Also check around the manifold for air leaks...When you removed the cat did you touch the intake or exhaust manifolds?