I have a 1973 350/250 and I just installed a rebuilt quadrajet carb.  The idles and runs fine, however when I start it cold it belows out white smoke for an instant.  That did'nt happen with my old leaky carb.  I made varous adjustments however no change.  Any ideas?

Frank

white smoke should be an indication of water, not gas. Do a compression test and make sure you do not have a minor leak in one of your gaskets.

It could be a compression leak, but it could also be condensation in the exhaust.  With the rebuilt carb, it could be a bit leaner than before, and thus a bit hotter causing some condensation to form when shut off, and turn to steam right after it's started.   But check the head gaskets anyway, just to be sure.

Thanks for your help, I will check compression etc.

Actually, a minor coolant leak won't show up in a compression test.   It would be better to do a chemical block test.   This is where a fluid is put in a chamber with an air stone, and held on the radiator opening.   Any vapor from the rad will go up through the container and air stone, bubbling through the test fluid.  If any compression is leaking into the water jacket, it will find it's way out of the radiator and turn the color of the test fluid.

NAPA has these kits/testers.  Autozone did, but may not now.  Or a decent shop can do the test.

I had a white smoke problem with my car on start up,at the end of a downhill run coasting, and after slowing down after sustained high speed driving. The actuator valve on my turbo400 trans was faulty,and this resulted in the transmission fluid being sucked up into the intake manifold and fouling no.7 sparkplug. If you have auto trans you can check by pulling the hose off of the valve (right hand side on a T400) and checking for fluid-fluid loss indicated diaphram is shot.

Thanks I will check the trans