I have been maintaining FX for almost 3 years and first of all never reply on one single mechanic, for each work search for specialist, take one or two option for all the work you do. if you have carburator issue visit specialist same as for suspension because mechnic will say we will do it all and bla bla but woh apna khancha mein laga rahta hai
First as for un stable at first and 2nd gear it could be due to bad foundations (all 3 or could be any one), than proper tuening could be the reason, if you have not change the plug fires since you purchase do change that as well or at least check it.
Their is one mechanic name Irshad at Tariq Road, near tip top try cleaner his mobile no is 0300 - 2237538, do visit him he is very good mechnic he also got compression test facility if their is some thing related with your engine.
Also try to do some basic maintainance by your self