Is the distributor supposed to shake back and forth? It appears to be on some kind of slide bracket that allows it to move, and there is a line from the carb back down to what looks like an air pump that causes this. Can someone explain how and why this all works? Thanks!
Shake? Well it is supposed to move but not shake, basically, when your engine is ticking over it needs the spark to be just before the piston in the engine gets to the top of its stroke, only a few degrees before, if this happens all is well and it idles away quite happily, but when you stomp on the gas pedal the engine needs the spark to be a tad earlier than a few degrees, and later engines do this by having the plate inside the dizzy twist, the plate that holds the points, so the timing (when the spark is sent to the plug) changes, your engine does the same thing but by turning the whole distributor, this is done using the vacuum from the carb, at idle there is a little bit of suction down the pipe but when you open up the throttle there is more suction and it twists the distributor round and gives the engine a earlier (advanced) spark and off she goes till the engine isnt working so hard and the vacuum drops off, putting the timing slowly back near the idle point when your just cruising down the road, If your dizzy is shaking then something is worn or lose, it should twist with a minimum of play.
Maybe shake was the wrong word, it is twisting back and forth, so it sounds like the vacuum advance. I'd just never seen it before.
Movement Well as long as its just twisting and its running ok, then you dont have a problem old chap, ifn its doing an irish jig and its running real bad then its different story
Yeah, it's wagging back and forth, that ain't right. As I understand it, the distributor should twist along the arc as vacuum increases (i.e. when you press the accelerator). This thing is flopping back and forth at idle. I'm assuming there's a rubber valve or reed or something inside the vacuum advance mechanism that has gone bad. It doesn't look serviceable, so I'll just pop in a new one and see what happens. Sucks that you have to take the distributor out to get it in, but oh well. I'm guessing this will fix it. It's running really rough, like the timing's bad (which it may be, anyway), but this should help.
Another thing occurred to me, what if the mechanism is fine, but I'm not getting enough vacuum from the manifold? I don't have a pressure guage at the moment, is there any shade-tree mechanic method of determining if there is enough vacuum? If there's not, is there an easy way to find the leaks, or do I just start replacing manifold and carb gaskets?
If it starts quickly, runs smoothly, and doesn't smoke a lot then your vacuum is OK. You lose vacuum mainly due to valve problems and if rings are really bad but it'll smoke like a chimney by this time. Advancing or retarding timing will also change the vacuum reading. A cheap vacuum gauge is probably around 20 bucks and is a multi purpose tool. Read the chart that comes with one and it will show how to check the valves, timing, and even the fuel pump since most have a pressure scale also. Continue to ask questions and work on your truck; before long you will be giving answers.
Dizzy Wobbling Chick ; You're the victim of aDPO or DPM , the dizzy is now junk as someone let the engine lean on it when it was out of the truck , bending the shaft . this was a _really_ common occurrance back in the day ~ the dizzy MUST NOT have this wobble as the engine is running . The good news is : prefect used distributors are super cheap as these fine engines get tossed out on a regular basis . I bought a N.O.S. one for $50.00 off Flea-Bay . You can use either dizzy , the early , low cap 216 one or the later , high cap 235 one , I'd recomend the later one . The vacuum advance fits either one .
That could be, but I think it's a faulty vacuum advance. I will replace it tonight and see. The distributor doesn't wobble at idle or when I disconnected the vacuum line. I think the valve inside the advance mechanism is not holding vacuum.
O.K. Then , It wasn't clear what movement you had . NAPA's Echlin and also Standard Ignition still carry the vacuum advance . Remember : it connects to the vacuum source on the CARBY , not the intake manifold ! there should be no vacuum @ idle and it gradually increases as you speed up the engine .
Yeah, it's connected to the carb, I misspoke. I bought the new mechanism from Classic Parts today, so I'll try it out tonight and see what happens.
Ok, installed the new vacuum advance mechanism and same result. At fast idle or above, the distributor jumps back and forth. At slow idle or if I disconnect the vacuum line, it does not. a) This leads me to believe that I'm losing vacuum intermittently somewhere else. Is this correct? If so, where would that be? Carb base gasket, intake manifold gasket, etc.? b) Could this be related to my other "dead cylinder" problem (https://talk.classicparts.com/showthread.php?t=8981)? For example, if the valves were out of adjustment or stuck, would this create an intermittent vacuum problem? I'm not sure if my two problems are related or not. I think I need to start at the beginning by checking the valves, then setting the timing manually, checking points and spark plug gap and finally setting the timing with a light. I don't think I've lost compression in those cylinders, I think something is just way out of adjustment.
Yes , a valve is stuck or burned causing vacuum pulses in the intake . ~ this is exactly why I always say to begin with a valve adjustment .
Guru Ifin i was you i would listen very carefully to Nate, he's only been wrong once, it was a wednesday, 23rd of feb 1979!
Just to tie up a loose end, this was solved in conjunction with my dead cylinder issue here: https://talk.classicparts.com/showthread.php?t=8981
