viven44 Posted February 22 Author Share Posted February 22 The springs in the distributor pull the advance back towards zero. The restriction keeps the plate from being able to move too quickly. But the restriction also must provide some kind of limit to manifold vacuum. We see that in how it's implemented in the system OK thanks! I'll need to use my old bad distributor (with a bad bearing) as a test vehicle to practice/learn about some of these things. Link to comment Share on other sites More sharing options...
Gary Lewis Posted February 22 Share Posted February 22 I think there will always be some flow, we are talking only 20" Hg or less, which is several orders below absolute vacuum... Edit: Also what happens when the vacuum advance is not in effect (when throttle is changed).. it has to go somewhere.. does that count as a "bleed" Link to comment Share on other sites More sharing options...
viven44 Posted February 22 Author Share Posted February 22 Thanks for making this video, I never doubted that you won't hold vacuum in steady state.. I THINK you need a constant source for this to work properly. My comments do read that way and I apologize, what I meant (or now mean) is that with a constant vacuum source/air pump such as an engine, with a restricted line, you won't be able to pull that much vacuum as you are pulling with the MityVac. I don't think the vacuum reading on the gauge is a good indicator of how much vacuum advance happens, it may be inversely proportional. I don't know much about how vacuum advance works but 1) Would it be possible to see how much advance happens on the distributor with varying vacuum hose diameters on the MityVac ? 2) same above but with a constant 20" Hg vacuum ... Shop vac? or engine ? Link to comment Share on other sites More sharing options...
Gary Lewis Posted February 22 Share Posted February 22 Thanks for making this video, I never doubted that you won't hold vacuum in steady state.. I THINK you need a constant source for this to work properly. My comments do read that way and I apologize, what I meant (or now mean) is that with a constant vacuum source/air pump such as an engine, with a restricted line, you won't be able to pull that much vacuum as you are pulling with the MityVac. I don't think the vacuum reading on the gauge is a good indicator of how much vacuum advance happens, it may be inversely proportional. I don't know much about how vacuum advance works but 1) Would it be possible to see how much advance happens on the distributor with varying vacuum hose diameters on the MityVac ? 2) same above but with a constant 20" Hg vacuum ... Shop vac? or engine ? I had a constant 22" of vacuum on the dizzy. The Mityvac has a check valve, so if there's no leak then the vacuum is constant. And I don't think the size of the hose will change that - unless you get to an extremely small hose, much smaller than we have on these vehicles. And the amount of advance is proportional to the amount of vacuum. However there are springs in the vacuum advance canister that the vacuum has to overcome, so that determines the start point for the advance. That might be in the 10 - 12" of vacuum, but some canisters are adjustable for that - see the Crane Cams instructions for that. Link to comment Share on other sites More sharing options...
viven44 Posted February 22 Author Share Posted February 22 I had a constant 22" of vacuum on the dizzy. The Mityvac has a check valve, so if there's no leak then the vacuum is constant. And I don't think the size of the hose will change that - unless you get to an extremely small hose, much smaller than we have on these vehicles. And the amount of advance is proportional to the amount of vacuum. However there are springs in the vacuum advance canister that the vacuum has to overcome, so that determines the start point for the advance. That might be in the 10 - 12" of vacuum, but some canisters are adjustable for that - see the Crane Cams instructions for that. OK I think i get what your are saying. Going back to the electrical parallel, current flow would be proportional to resistance of the load and anything else in series, and if the load past the series resistor was an infinitely high resistance there would be no current flow, thus no voltage drop across the resistor. In vacuum, since your distributor has infinite resistance, there is no air flow, so there should be no vacuum drop past the restrictor, but I am also intrigued by how the vacuum restrictor works.... One possibility is that the vacuum restrictor is a controlled vacuum leak device which would limit how much suction is placed on the distributor. If it is, should be called a "vacuum leaker" lol... Sounds like a case of marketing taking over. I still have all the emissions parts I pulled from my donor truck. Hoping it has a restrictor. I'll play with the restrictor and see how it works. Some of the other things were broken with age so I decided to not reuse any of it, maybe there are bits and pieces that can be reused. Link to comment Share on other sites More sharing options...
Gary Lewis Posted February 22 Share Posted February 22 OK I think i get what your are saying. Going back to the electrical parallel, current flow would be proportional to resistance of the load and anything else in series, and if the load past the series resistor was an infinitely high resistance there would be no current flow, thus no voltage drop across the resistor. In vacuum, since your distributor has infinite resistance, there is no air flow, so there should be no vacuum drop past the restrictor, but I am also intrigued by how the vacuum restrictor works.... One possibility is that the vacuum restrictor is a controlled vacuum leak device which would limit how much suction is placed on the distributor. If it is, should be called a "vacuum leaker" lol... Sounds like a case of marketing taking over. I still have all the emissions parts I pulled from my donor truck. Hoping it has a restrictor. I'll play with the restrictor and see how it works. Some of the other things were broken with age so I decided to not reuse any of it, maybe there are bits and pieces that can be reused. If the VREST does have a vacuum “leak” that would explain how it keeps the vacuum to the dizzy low. Otherwise I can’t see how it would work. Link to comment Share on other sites More sharing options...
viven44 Posted February 23 Author Share Posted February 23 If the VREST does have a vacuum “leak” that would explain how it keeps the vacuum to the dizzy low. Otherwise I can’t see how it would work. OK we are back to square one. Looks like it is just a smaller opening restricting vacuum. Found this in the 84 Factory manuals -Emissions/Diagnostics book, which for some reason is a larger book than the engine book It is an interesting read, I have never picked up that book until now. Link to comment Share on other sites More sharing options...
Gary Lewis Posted February 23 Share Posted February 23 OK we are back to square one. Looks like it is just a smaller opening restricting vacuum. Found this in the 84 Factory manuals -Emissions/Diagnostics book, which for some reason is a larger book than the engine book It is an interesting read, I have never picked up that book until now. Cool! So now we now the orifice sizes, although I'm doubting there are any jets around that small. I need to record this for posterity. Link to comment Share on other sites More sharing options...
Gary Lewis Posted February 23 Share Posted February 23 Cool! So now we now the orifice sizes, although I'm doubting there are any jets around that small. I need to record this for posterity. It is now in my copy of the Master Parts Catalog, as shown below. But it turns out that there are two different part numbers that are red, although I'm assuming they have the same size orifice. Link to comment Share on other sites More sharing options...
viven44 Posted February 23 Author Share Posted February 23 It is now in my copy of the Master Parts Catalog, as shown below. But it turns out that there are two different part numbers that are red, although I'm assuming they have the same size orifice. Very cool. A cheap source of these orifices would be flux core welding contact tips and a rubber hose on either side. I know there's 0.025, 0.030 for sure, Not sure about 0.020 and 0.015. I don't believe a 0.025 tip would have a 0.025 opening though. There should be tolerance built in so its probably a larger opening. https://www.harborfreight.com/0025-in-mig-welding-contact-tips-10-pack-63796.html Link to comment Share on other sites More sharing options...
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