Mitsubishi Repair: timing and miss firing, crankshaft pulley, correct tension

Question
i own a 90 eclpise 1.8l. i recently got my timing belt changed and since then i have had problems with my car, the guy is reputable, i taken my car to him for many years. he did my timing belt before with out problems. anyway, after i got it back i noticed it was miss firing and running rich. but it will only miss fire every time i start my car and a few minutes after, then it will just run rich while i drive. i checked the timing and i had it at 7BTDC and now its way off, like at 12 or 15. do you think the timng belt was installed wrong or something. i have also been told that if the BALANCE belt is off it will make my car miss fire too. but how can that belt affect the timing. i dont think it can be the plugs, and wires, i just replaced them thinking that might be it. i doubt it is the distributor, but i am planning on replacing it to see if it solves it. at about $2.35 for 91oct gas i can aforred to go olny about 12 miles to half a tank much longer. any help i would appreciate. thanks.    oscar

Answer
Oscar,
Don't bother with the 91 octane fuel.  That's really only meant for higher performance engines.  If you just use a good fuel system cleaner like STP, that will help with cleaning out your fuel system.

Some of the best mechanics have a very difficult time with timing belts on small engine cars.  And the biggest problem is that they screw up the balance belt.  When the balance belt is installed, the crankshaft pulley MUST be aligned with the oil pump sprocket, or else you'll have problems like you're describing.  This problem is not as prevalent in the SOHC (single overhead cam) engines like yours, but it's still important for the mechanic to get it right.  If everything is not aligned properly and set to the correct tension, you will experience many problems.  I've had balance belts that have snapped only days after that it had been installed.  Many mechanics will swear up and down they installed the balance belt correctly, because they do not want to go back and check (it takes about 3-4 hours for the average mechanic to remove and install a balance belt).  

Take your car back and insist they re-check the alignment on the balance belt, so both you and your mechanic can be 100% positive that it is (or isn't) the problem.  Once you can rule out the timing belt and balance belt, all other things to check are relatively easy.
Good luck!