The Stovebolt Site Forums The Shop Area Engine Shop Ported vacuum Carter on '59 235

A couple of other points...GM has spark advance curves shown on the Heritage pages for each year and while they are not all the same for the 235, they don't deviate by much. The 1959 235 represented changes that may not be completely understood now. The camshaft was changed and certain other things as well. There was a copy of an interesting internal memo explaining the changes to dealerships. I wish I had saved it as it is gone now...it disappeared when they cleaned up the on-line pages. Mostly it had to do with GM's corporate decision to help eliminate smog and a move to make certain engines produce greater torque at lower rpms so less fuel would be necessary. The torque curve for the 1959 235 makes it easier to understand. Torque reaches a near-max at 1600 rpm and stays a nice flat line all the way over to 2800 rpm. If you study the data for other 235s (say the 1955 model), you'll see differences in the content and how it is presented. For one point the spark advance is shown with rpm data and it is clear no spark advance happens before 500 rpm...and vacuum advance doesn't kick in until around 1800 rpm. But again that's for a different design.

Another point. The Carter YF3211S (which is an auto choke model) was the one Carter engineers came up with for the 1957 through the end of production of the 235. As you might expect it runs a little leaner and sits a little lower (because of hood/body style changes). Also it used a 2 stage metering rod. They're not always easy to find these days, but worth watching for I think.