How much vacume is good without any leaks when having a stock setup with a single carb and single intake manifold ? How to measure the vacume (gadget) nearby the manifold senter brass inlet coupling ? Will vacume increase when installing a dual intake manifold with 2 Carter Weber carbs like the onces i bought from Tom langdon ? Thanks Martinius.
18 to 21 inches. Eighteen will run strong and smooth but with a factory cam but around twenty shows an engine in really good shape. If the butterflies (throttle plates) are closed on either one, two, or three carbs then the vacuum will remain the same at the manifold port. Most vacuum gauges come with a diagnosis sheet that has some really good information on it. They can be used to check out evrything from timing to worn valve guides.
Thanks Even for the information I will have my son to measure the vacume for me as he baught the gauge a while ago to measure his 500 cc Rotrax airplaine engine. Thanks a lot Even.
Intake Manifold Vacuum The ignition timing has much to do with it ~ too much advance will raise it right up but can damage the engine . Most important is a steady reading @ hot idle . My current truck's worn out 250 CID L6 has 15" @ idle in gear ,this engine wants TDC ignition timing for some odd reason ~ it runs peppy and smooooth as silk so I leave it ~ on a perfectly flat road , I can feather the throttle @ 55 MPH and still get 15" of manifold vacuum . Your 235 will run best near ball on pointer , you're supposed to do a "Throttle Ping Test " after every tune up and give it as much timing advance as it'll take without ping or knock when you stamp the throttle @ 35 MPH in high gear . If the gauge's needle makes a rhythmic ' tick ' @ hot idle , that's a miss even if you can't feel it , prolly a sticky valve caused by wobbly valve guides .
Most greatfull for the advice ! Looking foreward to get the testing done and implicate all your advices when measuring the vacume. Thanks a lot Martinius.
