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By Dave V - 11 Years Ago
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I'm confused on timing my new rebuilt 312. Trying to time it by the vacuum method along with a timing light. As I advance the distributor to increase vacuum reading it does run much better but the vacuum advance can hits the intake manifold when I reach 17" hg @20 degrees advance. I'm sure I could get a higher vacuum reading yet if I pull the distributor and rotate it a notch but I'm concerned about the initial advance climbing over 20 degrees. The engine does have an Isky E4 cam advanced 2 degrees, the Mr. Gasket lighter advance springs along with a rebuilt distributor modified per a post here to give 26 degrees centrifugal advance. Is it possible the springs are too light allowing extra advance @ idle or? Dave v
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By charliemccraney - 11 Years Ago
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That's one reason I don't time with vacuum. You may find that the engine is hard to start and you will have far more total advance than you need. It's not likely that the springs are too light. You can test it by reving the engine slowly with the vacuum advanced disconnected and watching the timing marks. If it advances immediately, then they are too light.
It also seems like an E-4 should have more vacuum than 17 with a more normal initial advance setting. What is your idle rpm?
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By The Master Cylinder - 11 Years Ago
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Dave V (4/12/2014)
... it does run much better but the vacuum advance can hits the intake manifold when I reach 17" hg @20 degrees advance. I'm sure I could get a higher vacuum reading yet if I pull the distributor and rotate it a notch but I'm concerned about the initial advance climbing over 20 degrees. Dave v
Dave, what is the condition of your damper? Did you verify TDC? If not it could have spun and your timing marks are NFG. I time my 312" with a vac gauge and find it runs best at 18" hg which equates to 16° advance.
Here's a link to a thread where I had a similar question as yours. http://forums.y-blocksforever.com/Topic88289.aspx
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By Pete 55Tbird - 11 Years Ago
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Dave
Your first question was what to do about the distributor vacuum advance can hitting the intake and limiting the amount of advance you could set. Either pull the distributor and jump one tooth or pull and replace the ignition sparkplug leads on the distributor cap as needed.
The weight or strength of the advance springs is what controls the rate of mechanical distributor timing as the engine RPM is increased. The total is controlled by stops on the distributor plate and is a function of RPM until the limit is reached.
The distributor vacuum advance should be disconnected and plugged while timing the engine.
Go for highest manifold vacuum and as the timing is advanced the RPM will increase and the manifold vacuum will increase too. Then back off 1 or 2 inches of manifold vacuum. Road test and listen for pinging and hard starting while hot. As many others have said limit total mechanical advance to 34/36 %. Pete
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By Dave V - 11 Years Ago
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Thanks for the replies. I was gone yesterday and did not work on the car. To answer your questions, I did have the vacuum line disconnected from the advance can and plugged at the carb, idle 550 RPM, degreed the cam when assembled & found TDC, checked the damper for accuracy and even put a scribe mark on it @ 38 degrees. Master Cylinder: I really appreciated your article pertaining to the same problem. Is it still running ok? I will be working on the engine again today and check the rate of advance on the lighter springs. I forgot to mention that I do have a Pertronix II in this distributor and the coil to match. I'll reply to all later. Thanks again Dave V
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By MoonShadow - 11 Years Ago
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Moving the wires one notch is a quick and simple solution. Of course the "correct" way would be to move the distributor but either way will accomplish the same thing. Chuck
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By The Master Cylinder - 11 Years Ago
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Dave V (4/13/2014)
...Master Cylinder: I really appreciated your article pertaining to the same problem. Is it still running ok? I will be working on the engine again today and check the rate of advance on the lighter springs. I forgot to mention that I do have a Pertronix II in this distributor and the coil to match. I'll reply to all later. Thanks again Dave V
Dave, still running good, starts easy.
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By Dave V - 11 Years Ago
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I did get back to the engine today. I rotated the distributor 1 tooth so that the #1 on the cap is correct. Started to set timing again and found the light Mr. Gasket springs started advancing timing @ 900 RPMs and stopped advancing @ 1850 RPMs. I was getting a fluctuating needle on the vacuum gauge which I realized was coming from the 600 Holley leaking fuel thru @ idle. Installed a pressure gauge and found 8 psi fuel pressure coming from my FE fuel pump. Made a makeshift bleedoff in the fuel line to hold the pressure @ 6 psi and the engine ran very well. I will pick up a fuel pressure regulator and start over. I'll keep you posted. Also, is there a way to remove the temp sending unit bushing in the cylinder head. The old sending unit for my 56 is 3/8" pipe but the bushing in the 57 G head is 1/4"? Dave
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By The Master Cylinder - 11 Years Ago
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Dave there is a puller available for the sending unit bushing, from the normal repro parts places. I got mine from my go to place, Tee-birds Products. http://www.tee-bird.com/catalog_search.cfm
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By Dave V - 11 Years Ago
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So this is just a press in bushing? I should be able to pull it out with a slide hammer screwed in to it? Dave
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By Talkwrench - 11 Years Ago
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Dave just to let you know I have a Pertronix ing 3 and the 925D springs in mine with a modified timing plate, advance starts almost straight away and stops around 2400 rpm, advance quite quick. my timing [if I remember right] is 13 initial and total at 34 . Vacuum on top runs it up to mid 40's . Mine is an auto and a little tired I get 19 - 20Hg out of gear.
I Would not have thought you would get much more than17 Hg with your cam, maybe Ted or Tim would know for sure?
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By Dave V - 11 Years Ago
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I did order a fuel pressure regulator from Summit and expect it to come in today. Hopefully I can install it right away and do some more testing. I did remove the temperature sending unit bushing with a slide hammer. Worked well. Installed the 56 one. Will keep you posted. Thanks Dave
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By Dave V - 11 Years Ago
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Found time to get back to the 312. Installed the fuel pressure regulator and had to set it as low as 5.5 psi to prevent fuel from leaking thru the carb while idling. New problem though. When I turn the engine off gas drips from the secondary throttle shaft on the passenger side. The engine does run very well. Maximum vacuum is 18" so I backed it off to about 16.5" which gives 18 initial timing @ 500 RPM, 38 total. I'll try it out on the road this weekend. Dave
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By The Horvaths - 11 Years Ago
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Yes, it's a press-fit bushing. I made a slide hammer tool with some pipe, a pipe cap, and a steel disk. A gentle nudge with a propane torch helped a lot. Some sealer helps when putting the new one back in.
Edit - didn't make it to the second page before responding. Stupid cell phones!
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By Dave V - 11 Years Ago
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I did get the car out yesterday and was very pleased with the way it performed. I did have to drop the timing down from 18 to 16 degrees initial ( had a slight pinging ). Put about 50 miles on it and no problems. Thanks for all your help to get it to this point. Dave
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