Firstly, the Civic 1200 engine is an extraordinarily strong little machine which has high rev capability. To exploit this some good cheap modifications which can be made easily are the fitting of a sports exhaust and perhaps a Weber carburetor. The sports exhaust is easy enough, with a set of extractors, a hotdog and a turbo tailpipe should give you a bit more power by freeing accumulation of exhaust gases. Genie makes a good tailpipe; the hotdog can be bought anywhere. As far as extractors go, well in Australia there is a header pipe made by Hurricane, this is all there is for the Civic 1200.
Installation of a Weber is where real performance comes from at this level, note that this is not effective without a decent exhaust system. We have used two types of Webers, the best seems to be the 32 DGV model which is an aftermarket carburetor used on about everything up to 2 Liters. DON’T believe anyone when they tell you this is the wrong carburetor for a little Honda, from my experience so-called experts haven’t a clue about the capabilities of these cars! On my own Civic I have a 32 DIR 21 model which comes from a Renault 12, a father picked it up for about 40 $AUS from a wrecker.
Fitting it is easy: Tear off the old carburetor and air filter. Get an adaptor plate, Lynx makes one for a Datsun 1200 for about 25 $AUS, which is the one to use. Since Dattos use the same Hitachi carburetor, obviously this will work. Get another air filter, we have tried lots of tricks here, but the best seems to be the RAM Flo type filters, once again they cost about 25 $AUS.