[JP Noonan]

My 75 2.0L (same FI as the 1.7L) had a similar problem. Ran great until warm. In my case it was a bad inline resister some PO had put inbetween the CHT sensor and the harness. If you don't have one then I'd agree with DD check that the CHT in working properly. Look at the Tech Article section on this site and the 914 club site, there is a D-Jet testing article that tell you how to test the CHT sensor.