Hey Folks , Great site , Sure hope someone can steer me in the right direction, Heres the story thus far , She's a ole 73 Comet , 302 , 2 barrel carb , The Carb has been re-built , or at least a kit was put in it , that helped quite a bit . ( I think theres something funny with the power valve however) ,, Anyway fresh tune-up , cap , wires , plugs- motorcraft. , New points, Set with a dwell meter . Just had head gaskits too. was checking things over , On the Vac. gauge its only showing 15 inches, if has a very small bounce like less then a 1/2 inch. I turned the engine over by hand , brought #1 up to T.D.C., pulled the dist. an reset it so the rotor button was pointing dead at the #1 term on the cap . { took a magic marker an made lines every where so I know its rite} , Put a blunt screwdriver down #1 to make sure piston was all the way up , Rocked the crank back an forth several times to make sure it was dead on.I know it was on Compression stroke .I have tried adj. the carb , even before it was overhauled, Still all I can get is 15" of VAC. I checked for vac leaks , using carb cleaner , an then hated to do it but got a squirt can an used motor oil to try it. Nothing { Eng, needed a bath anyway }My timing marks line up with the damper,. From what I read it says cam timing , Pulled valve cover an rolled eng , both valves apper closed + just had heads done, So I give up what is it ????? , On my other cars I've gotten 20- 21" at idle, I dont know if this is why its kinda doggie ???, Could someone had put timing chain on wrong ?? , Could the cam be worn ??? Or have I missed something ??. I sure hope one of you guys know? , Thanks in advance
I don't know much about timeing, but I don't think you want it fireing dead exactly on TDC. I know my car dosen't.
Is the idle nice and smooth? Anything that affects idle quality will affect the vacuum level, timing, rich or lean mixture (that's why you should set idle mixture screws with a vacuum gauge), internal carb air leak or fuel leak, etc. As mentioned above initial ignition timing should be set to somewhere around 6-10 degrees BTDC. BTW, no such thing as a vacuum leak, it's actually positively pressurized air drawn in to where there is supposed to be negative air pressure. One of the few things I remember from Physics class so many decades ago.
vaccum Ok guess I failed to mention , yes I know your not suppose to run your engine at TDC, unless the book calls for it .....I set the Timing with a light to Specs after I fired it up.6 degrees BTDC . I just wanted to make sure ---Starting off that the timing was dead on .... I wanted to make sure that the Dist. wasnt off time by a tooth or so, you never done this ?? replace a dist. an re-time it to the eng . ??? When you replace your timing chain you line up the dots / hash marks-- which happen to TDC...... An I guess were splitting hairs as to postive - negative pressures --- In layman terms if your sucking air somewhere your not suppose to be . It commonly called a { vaccum leak } . least how when I got my first ASE patch ,10 yrs. ago for automotive tune-up that was good enough to pass the test !!!!, An yes I used A Vaccum gauge to set the carb.Yes it has a stable Idle at 6 degree's BTDC , Idle set At 625 RPM,,,, I adjusted the Carb to get the highest Vac. reading possible if I tweak the screws one way or the other by a 1/8- 1/4 turn my Vac. drops off.. ,, However as I was playing around I found if I cranked the Idle up , or Advanved the Timing it would bring my Vac. up,,, However that put me way out of NORMAL Specs, were talking like 15 degrees advanced , An Idle like 1200 RPM, Hopefully someone can tell me why it has low Vaccum,,,, Thanks
Check your intake gasket if its out of place a bit or if its not torqued down properly it can cause low vacuum, and remeber engines wear out as the get old things dont seal like they used to. check for cracks in the lines. low vacuum isnt the end of the world i only have 2 line on my car and they go to the transmission my distrubtor is a non vacuum and i just have a little breather for a pvc.
