Rebuilt 2.7 engine refuses to work properly

[72targa]

^^^^ seems that measuring what is going into the engine would be a logical starting point. Hence, measuring the air/fuel mix. Ed knows a thing or two about these cars.

[Einar Irgens]

Well, the AFR was measured this summer, before I went to pick it up from restoration. I was told then that the AFR was about correct both at idle and at higher revs, and that engine ran ok (I strongly disagree with the latter, even though I'm not at all hard to please).

Today I ran a cylinder leakage test, and everything appears to be in order. I also took off the valve covers, and found no loose or missing parts anywhere.

I should mention another symptom that for some reason has become more apparent lately. If I cruise at a steady speed, and then suddenly open the throttle more than about three quarters, a rather audible flapping sound appears. This happens no matter what gear is engaged. Throttle respons is quite good, but that sound scares me. Knocking, perhaps?

Edit: About the last paragraph. To be more precise - If I cruise at steady speed of e.g. 20 mph, and then suddenly open the throttle more than about three quarters, a rather audible flapping sound appears. This happens no matter what gear is engaged. So - the sound appears independent of rpm.

[Einar Irgens]

Update. I had to leave the car in winter storage without having solved the engine issues However, recently obtained some interesting new information.

I first contacted a guy in Norway who from time to time does carburetor tuning for 911 owners, mostly Webers. I asked him if he had ever experienced uneven power delivery due to carburetor faults. His answer was that clogged idle jets can result in this kind of behavior. I have of course blown through the jets with compressed air several times, but perhaps they should be left submerged in thinner for a while too, given that the hole is so small.

I then wrote to Paul Abbott of Performance oriented and asked the same question. His answer was that the idle air correction jets may not have the proper size for a ported engine with increased displacement.



This jet is not easily replaceable, but he has developed an adjustable version, which I have now ordered.



The fouling is noticable at least up to 4000 rpm. I thought the idle/tranition circuit only was participating up to 2-3000 rpm, but Paul tells me that it supplies air/fuel all the way up to 5000 rpm. Of course, the main circuit gradually takes over, but still definitely worth checking out. Which I will do in the springtime, in "just" six months