Re: '56 Rochester 4GC

Posted by John Payne On 2012/11/5 3:09:01

Thanks Guys. Time for a report on what happened over the weekend, and I've got to say it's good news. We did a total of 550 miles under various conditions, most of which was highway but speed varied depending upon what we were doing, and the outside temperature determined whether to run the A/C or not. After saying all that the best mileage I recorded was 20.4 aussie mpg, which equates to 17.0 US mpg. That was for about 75 miles of pretty much flat highway at around 50 - 55 mph, and no A/C. The only other recording I have at the moment is 18.1 mpg (15.1 US mpg) for 160 miles involving high and low speed running, some hills and about 50% with A/C.

This is as good as it's been for a long time and best of all, it was trouble free motoring for the entire weekend. I can only put this down to two things, and based on what Ross has said, I'm not exactly sure if this could be why. Firstly, I redid the vacuum advance pipe connection at the distributor to try and eliminate any leakage (I didn't think there was any), plus the carby idling jet adjustment mentioned in a previous post. I did also knock the timing back fractionally but I didn't think this would make much difference, apart from potential pinging (there wasn't any). What I can say is that the engine is now idling nicely, pulls strongly from take off and feels good while cruising. I was unable to read Ross's post until we returned today so I was going to report that the idling jet adjustment did wonders for running and fuel economy, but now I won't!

I might try using a vacuum gauge just to see whether further improvement is available, and I assume the objective is to maximise the amount of vacuum being shown, similar to what I was doing with rev's. I have noted Ross' advice and definitely won't thinking about number of turns any more. I've got to say that fellas such as me, who are mechanically minded but don't have the wealth of experience that is available on this website, really appreciate the advice we receive from you knowledgeable gents. Thanks once again. Regards, John