Trev is right. Nothing the OP could have messed up on the timing belt would change the ignition timing, as measured with a timing light. But that does not rule out improper alignment of the belt.

The belt controls valve timing at the cam sprocket -- a possible explanation for the back fire and idle problem. It also controls the selection of a plug to fire at the I-shaft sprocket; that one has to line up to make sure the path from the coil to the correct spark plug is complete regardless of where the computer puts the ignition timing.
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Art Benstein near Baltimore

With her marriage she got a new name and a dress.