rodneybeauchamp Posted October 25, 2017 Share Posted October 25, 2017 What should the vacuum gauge reading be on a 63 Riviera 401 at idle? Where should the reading be taken from? thanks Rodney Link to comment Share on other sites More sharing options...
Seafoam65 Posted October 25, 2017 Share Posted October 25, 2017 Take the reading from any vacuum port on the intake manifold or carburetor base plate that has full vacuum at idle. Normal reading would be somewhere around 18-20 inches of vacuum. Link to comment Share on other sites More sharing options...
Jim Cannon Posted October 25, 2017 Share Posted October 25, 2017 This is a problem on the '63 Riv with an original AFB carburetor. The vacuum port for the distributor is "ported". So it is not open to full manifold vacuum at idle. (Other later Rivs are not; this is one of the little differences between '63 and other years that drives the novice crazy.) So vacuum at the distributor port will not be correct (it will be very low). There is no little port on an original '63 AFB with unported vacuum to connect to. The little vacuum port on the front of the intake manifold for the A/C system has a check valve in it. You can't use that. I hate messing with the power brake vacuum line, but you could temporarily connect there, if you wanted to. So the easiest place to pick up full manifold vacuum is on the PCV line off the back of the carby. Use an adapter to "Tee in" a vacuum hose size that your vacuum gauge will connect to. Keep the PCV valve connected (so that idle mixture and RPM are not impacted by your gauge). At idle, you might see 18-20" Hg, but you don't need to see more than 17" Hg. Depending on your cam, you may only see 16". More important is to look for a steady needle at idle and up, at higher RPM, to indicate all valves are moving freely and sealing well. Reading and interpreting vacuum gauge readings is a bit of a learned art. You can do a lot of diagnostics with one, once you learn how. 2 Link to comment Share on other sites More sharing options...
Seafoam65 Posted October 25, 2017 Share Posted October 25, 2017 I get some cars in my shop with very wild camshafts that produce only 8-10 inches of vacuum at idle. In some cases on cars like that with power brakes it is necessary to install an aftermarket vacuum pump to the car to work the power brake booster. I absolutely detest monster cams in cars, but the first thing the average car enthusiast wants to do is go into the Jeg's catalog and buy the wildest most unstreetable camshaft that they can buy. Link to comment Share on other sites More sharing options...
rodneybeauchamp Posted October 25, 2017 Author Share Posted October 25, 2017 Thanks Jim and Winston. I bought a used gauge of reasonable quality (made in USA) at a recent swapmeet and after trying the port for distributor vacuum advance and the take off for the heater & air conditioner vacuum, was wondering if I had a dud gauge. Your replies make me optomistic as the readings were low. Will give the PCV valve a go with a made up T. And take your point about the readings being steady, will also look for that. Rodney ????? Link to comment Share on other sites More sharing options...
Bill Stoneberg Posted October 25, 2017 Share Posted October 25, 2017 Check this image out 2 1 1 Link to comment Share on other sites More sharing options...
jsgun Posted October 29, 2017 Share Posted October 29, 2017 Vacuum gauges are awesome. I used to tune the timing and carb on my ford with one. Link to comment Share on other sites More sharing options...
JZRIV Posted October 29, 2017 Share Posted October 29, 2017 Guess this is one topic where you want an engine that really sucks 4 Link to comment Share on other sites More sharing options...
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