1990 Oldsmobile 88

Hi guys,
I have a 1990 Oldsmobile 88 with 81,600 miles on it.
I recently just changed the exhaust system and gave it a tune up. I also changed the electronic distrubutor. When I start the car after it has been sitting, I get a smell of gas, as if the car was a boat. Even though the car is almost 19 years old, I have no miles on it really. I also recently had the timing belt changed around 70k and ever since then the car doesn't run right. I brought it to the mechanic and he said the timing was correct. Why does my car have the shakes? And what could the smell of gas be coming from?
Thank you!