Just installed a Ram Jet 502 in a 69 Chevelle, car has severe vibration from idles rough, smooths out between 1200 & 1800, anything over 2000 vibration gets worse.
Engine came equipped with a flexplate with a big weight on it. Not thinking, I installed my flywheel.

Any ideas?

That would be the problem....Always read the instructions first...:D

What's the flywheel off of?

402 small block

scratch that, i meant 402 big block

mean,
That is the problem. The 502 is considered an "externally" balanced engine and has to have the weight on the flywheel to keep it balanced. You need to put the original flywheel back on. If you need a manual transmission flywheel, you have to purchase the correct one for the 502, it is listed in the GM Performance Parts catalog. As an alternative, if you have a good balance shop near you, take them the original 502 flywheel and the 402 flywheel and have them balance the one you need to match the original.

By the way ... DO NOT run the engine any more until you get it fixed, you can very easily "kill" a bearing with a flywheel that far out of balance.

I don't have an original 502 flywheel, I used the flywheel off my old 402 big block. I have the 502 flywheel getting shipped overnight. I put approximately 8 - 10 miles on motor @ low rpm. That shouldn't have hurt it, should it. Hopefully not, we'll find out tomorrow.

Any help would be great. Thanks to all. I'll let you know how it works out.

Problem fixed, was flywheel. Thanks for all the help!!

Car is a powerhouse, woo hoo!!