Please help me diagnose this 273
- The advice to adjust valves is good.
- Ignore the compression readings and oil for now; they are not all that bad. Just put in some fresh plugs in the oiling cylinders. Those lower compression readings are NOT what is causing the running and idling problems. A 100% dead cylinder will not cause the idle to hunt up and down.
- With a stock cam the idle vacuum levels are indeed very low. this very much points directly at a vacuum leak. You can get 14 in vacuum easy with good tuning and a moderate cam at lower RPM's. You ought to be able to get 18 in +/- with a stock cam and carb, just a bit less with a 4 BBL.
- It's very probably a vacuum leak with the PO's manifold carb swap. When idling, slowly move a rag over the carb top to start closing it off and see if the idle improves. If so, then that is a very good sign of a vacuum leak.
- Could be at the manifold but start by pulling the carb and looking at the carb base gasket. If it is a stock manifold, it did not come with a Holley from the factor. So it could just be a wrong carb gasket not sealing.
- If no the carb gasket, then use the suggested methods to look for a manifold gasket leak. These tests are not foolproof, as a manifold gasket leak can come from the underside, in the block valley. The low vacuum levels are not normal so their is a leak somewhere.
- Pull the PVC valve from the valve cover and put you finger over the end. If it makes a small or no difference in idling, then that is not the issue.
- Check all hoses from the carb base or manifold to to anywhere for cracks.
- Make sure the secondary throttle blades are on the stop and those blades are almost completely closed. There should be a tinny gap between the throttle blades and the bores.
- Measure the voltage at the battery at a high idle... it ought to be 13.5 volts to 15 volts. This is to check that your new VR is OK.
BTW, I don't believe that a '67 273 would come with a nylon-toothed cam sprocket. So I don't think that should be pursued at this point.
