How do you check your can ??
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It should be easy to do with a timing light. You could also use a vacuum guage inline to monitor your manifold vacuum. Clean the timing index area on your harmonic balancer so it is easy to read. Start your motor with the vacuum line disconnected from the can. Set the idle as low as possible without stalling and record what your timing light shows the static timing to be. Reconnect the vac line and observe the timing after further lowering the idle again as low as possible to prevent the centrifugal advance weights from adding any advance while testing. Once you have your baseline you can make adjustments to the can. Remember to keep the idle down throuthout testing. Then you can adjust your idle where it should normally be and increase rpms with the vac line on and off to see ehat influence the adjustment makes.
There may be a better way but this should set you straight. If you have a vac guage you will be able to see at what stage of vacuum the can initiates advance.
There may be a better way but this should set you straight. If you have a vac guage you will be able to see at what stage of vacuum the can initiates advance.
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189 Posts
Hi lockjaw,I do have a vacuum gauge and a digital timing light. Today I was checking manifold vacuum,(12.5_14.5 [email protected]) , initial timing ( 8.3* ) mechanical adv. ( 16.9* @ 2500 rpm) From what I gather ,you get 10/15* from vacuum can. I just want to verify ,and identify where my timing is now . I'm not currently having any issues,just got done with carb/kd cable project and this was next. I'm going the manifold vacuum route and im just checking to see if this is in limits ......buy the way ..I'm re learning all this stuff.:beer: So just hook up vac to can with dist/cap removed and check ? Thanks .
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I just did this, on the bench, but my method should work for you, too. I used a vacuum hand pump with gauge to pull on the can. I watched to see at what vacuum the actuating rod stopped moving. My results were 16" Hg for an adjustable Moroso unit & 7" Hg for the OEM can on my V6 HEI. My tests show that the adjustment only effects the total throw of the actuator, and not amount of vacuum needed. Obviously I can't use the Moroso unit, because it operates way to high and ends up killing my economy because I'm never "all in".
To test while installed, I'd remove cap and rotor. Turn the engine by hand until you have a great view of the actuating rod and pickup. Attach hand pump and do the same test.
To test while installed, I'd remove cap and rotor. Turn the engine by hand until you have a great view of the actuating rod and pickup. Attach hand pump and do the same test.
The vaccum hand pump is what I've used in the past, however the only adjustment in the vaccuum advance can is the amount of advance, and not the actuation point.
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281 Posts
Adj Vac Advance timing
Need timing light and Mityvac pump. Warm up engine. Disconnect advance can end of hose and plug. Check idle speed and base setting. If possible, map centrifical advance. This will give you Initial plus centrifical total degrees. Connect Mityvac to vacuum can. Slowly pump while watching timing mark and record where timing starts to increase and stops. This tells you how much Vacuum advance and at what rate it comes in. Adjust can and repeat procedure. No more than 50 Degrees total please. Good luck.
Need timing light and Mityvac pump. Warm up engine. Disconnect advance can end of hose and plug. Check idle speed and base setting. If possible, map centrifical advance. This will give you Initial plus centrifical total degrees. Connect Mityvac to vacuum can. Slowly pump while watching timing mark and record where timing starts to increase and stops. This tells you how much Vacuum advance and at what rate it comes in. Adjust can and repeat procedure. No more than 50 Degrees total please. Good luck.
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This thread begs the old question of ported/timed vac or direct vac. I have an MSD box , coil and dizzy. Manufacturer wants me to use timed vac. My experi
ence tells me to use direct vac. I run 12 on the crank and 22 in the weights. The vsc advanc
e takes me to about 46. I have no pinging, but I might modify the can to give me a bit less. This is on a roller high compression aluminum head motor.:dontknow:
I have tried the timed vacuum. Works fine on the highway and creates a really nice tough idle rumble. The downside is that withot the vac adv at idle I must open the idle throttle setting to get the proper idle speed (900). In this condition when I shut it off hot it wants to run on and burp a lttle as it stops. I am considering changing the centrifugal stop and eliminating the vac adv alltogether. That kills mileage. With a Quick Fuel holley type double pumper I need all the help I can get with fuel economy. Car makes great power and speed. I am just tired tryi g to strike the right balance of stoichiometric and timing settings.
ence tells me to use direct vac. I run 12 on the crank and 22 in the weights. The vsc advanc
e takes me to about 46. I have no pinging, but I might modify the can to give me a bit less. This is on a roller high compression aluminum head motor.:dontknow:
I have tried the timed vacuum. Works fine on the highway and creates a really nice tough idle rumble. The downside is that withot the vac adv at idle I must open the idle throttle setting to get the proper idle speed (900). In this condition when I shut it off hot it wants to run on and burp a lttle as it stops. I am considering changing the centrifugal stop and eliminating the vac adv alltogether. That kills mileage. With a Quick Fuel holley type double pumper I need all the help I can get with fuel economy. Car makes great power and speed. I am just tired tryi g to strike the right balance of stoichiometric and timing settings.
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189 Posts
Hi all, ok Im getting a grip ,with the adjustable vac cans - you only have control of the amount of vacuum in the adjustment,and not when it starts/stops ok.
Lockjaw I didn't want to go there ,but yes that's where I'm at. I want to test the can like you all have suggested to see where its at in the timing equation
80v6 That's what I was looking for -- the how U do it part. I will do that test in the next few days.
There have been many articles on the subject I've looked at a lot . One of our members gave a link to a good read,but I don't remember where. Something like----- Mike goble Vacuum advance 101 He talks about having the correct can deployment ect.....
:beer:
Lockjaw I didn't want to go there ,but yes that's where I'm at. I want to test the can like you all have suggested to see where its at in the timing equation
80v6 That's what I was looking for -- the how U do it part. I will do that test in the next few days.
There have been many articles on the subject I've looked at a lot . One of our members gave a link to a good read,but I don't remember where. Something like----- Mike goble Vacuum advance 101 He talks about having the correct can deployment ect.....
:beer:
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189 Posts
Sorry, I forgot.
In the article he gives a huge list of cans and specs.so you can have a bit more control of timing. My can is marked AS-20 ,and wasn't on the list --- Anybody have knowledge on this can ????
STOP!------ Just found something, Summit page - Accel # 31035 " Accel adjustable vac advance chambers for GM permit infinite adjustment to both the amount and rate of advance."
It also is marked. AS - 20. Sooooooo. ?????? Somebody clarify please :dontknow::dontknow::dontknow:
In the article he gives a huge list of cans and specs.so you can have a bit more control of timing. My can is marked AS-20 ,and wasn't on the list --- Anybody have knowledge on this can ????
STOP!------ Just found something, Summit page - Accel # 31035 " Accel adjustable vac advance chambers for GM permit infinite adjustment to both the amount and rate of advance."
It also is marked. AS - 20. Sooooooo. ?????? Somebody clarify please :dontknow::dontknow::dontknow:
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2,102 Posts
the factory used a bushing on the advance can to limit travel and different spring pressure to control when it started to advance .the adjustable ones i have seen the adjustment changes the spring pressure therefore delaying or advanceing when the vacuum advance comes in.buy delaying when it comes in you also limit its advance because of the needed vacuum is increased to a limit greater than the engine will develop.the best way is to yus a hand pump and a timing light to set it where you need it for your particular engine set up and the vacuum range it runs in
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