Hey guys Im new to the forum but not so new to fords... anyway, straight to the problem

I have a 1988 escort 5dr 1.6 carb. On the way to work the other day it started running quite lumpy... was getting lose of power when accelerating, even backfired a few times. When I (eventually) got to work there was a strong smell of petrol after I just parked up whihc immediately made me think of a number of possible problems...

1) spark plugs need changing
2) HT leads need changing
3) Fuel filter needs changing
4) lambda sensor needs changing

I had an oxygen sensor problem when I had a 5 series and the symptoms were slightly different so I thought id go for the cheap options first and changed the plugs and ht leads, both to no affect. Now Im looking to change the lambda sensor to solve the problem as this is the next most feasible solution but, without meaning to look like a plonker, I cant find it on this car.... With my two previous cars the sensor was located just after the cat before the middle pipe of the exhaust but after sticking my head under the car I cant seem to see it. Can anyone either enlighten me as to where it is or suggest what else could be a possible solution? Many thanx in advance