smoking new engine

I have a new 350 chevy crate engine, it is the 260 hp version I put it in an old car for reliability I added a comp cams 292-501 cam and had the heads machined for comp cams dual springs ( this was done by a machine shop ) it also has an aluminum intake, headers, HEI, 570 Holley avenger carb. This engine has about 1000 miles on it if that. it has always run a little fat but since reassembly it has a serious smoking problem, it smells strong like gas fumes however I have jetted and re jetted over and over, I have tried 6 different carbs so far. I have removed and reinstalled the heads twice just to be sure even though I didnt find anything wrong. I have changed plugs over and over and new pcv valve. nothing seems to help the problem. its alot of smoke, it is very light gray in color. This is driving me nuts so if you have any advice please share, Thanks in advance to all who offer advice.

Welcome to AF, have you determined whether it is oil being burnt or a rich mixture?

I am not sure how to determine that, it doesnt seem to be oil there is normal condensation but when running there doesnt seem to be any oil coming out of the pipes.

Well, burning oil is pretty hard to mistake for burning coolant/water.

If it really is oil, look to see that you have the correct neoprene valve stem seals on the head. Generally there are 2 types for Chevys, the o-ring type and the umbralla type.

If these are missing, or of the wrong type there, the engine will smoke lots. Its possible when the new valve springs were installed, they were left off. Its an easy mistake to make, since not all engine designs use them.

Otherwise, burning coolant comes to mind, try pressure testing the cooling system. Use the correct tester with a pressure gauge and look for a slow pressure drop in the system.

I had thought of both of those things but had dismissed the valve seal thought because of a machine shop doing it, but you make a good point since the guys working there are human too. I will check that and if that isn't it I will move on to the cooling system. Thanks for your input and I will let you know what happens.

Update, after very close inspection of the valve seals I noticed that some of them had moved out of place and were letting oil through. I am in the process of replacing them with better quality seals that are more likely to stay in place. The moral to this story is, just because you had a so call professional do the job doesnt mean it isnt their mistake. Ahh brings back memories of the time I had a machine shop install cam bearings and they didnt do that right either. Many thanks for all the help!

Thank you for the update.

check the valve stem sealage.oil could easily come through there and itll smoke terraibly.id say the macheine shp did a crummy job.