Mechanical advance
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Post Fiend
Joined: Nov 2005
Posts: 7,437
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From: Charles Town, W bygod Va
Mechanical advance
Stock durasparkII system, I am getting 15 deg mech advance (vac unhooked) at 1500 rpm and it doesnt go any higher, at least not before 4500rpm. I diasembled the dist to find I have the 15l marking wich should be 30deg mechanical. Both weights move freely but one spring is a lot stronger than the other. I think I need a lighter return spring to let the second weight oovercome the spring to getr the other 15 deg it should have. The only other thing I can think of is the lighter spring is too light and advancing at idle. My question is why would my dist have a spring so stiff? Is this a normal thing from the factory?
Here is a link explaining the mech advanc operation http://www.reincarnation-automotive....ons_index.html
Here is a link explaining the mech advanc operation http://www.reincarnation-automotive....ons_index.html
pedant
Joined: Jan 2008
Posts: 23,576
Likes: 38
From: EXTREME southwest CT
In my limited experience it is not uncommon to see a '2-stage' mechanical advance with one spring much stiffer than the other.
Read step 13 of the Crane adjustable vacuum instructions:
http://69.20.53.62/pdf/271e.pdf
Read step 13 of the Crane adjustable vacuum instructions:
http://69.20.53.62/pdf/271e.pdf
Moderator
Joined: Jan 2001
Posts: 56,949
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From: Virginia
These are emissions engines. They run hotter and leaner, so they have to be conservative with the timing. Otherwise they ping. If you de-commission the smog and add a aftermarket carb and intake, and a 180 thermostat, you can usually get more aggressive with the timing curve.
I have also found they run way too much vacuum advance on the stock units. If you set your initial timing to around 15 degrees, and disconnect the vacuum advance, the throttle response and pickup is much better. But then you need to limit the vacuum advance if you want to hook it back up.
I have also found they run way too much vacuum advance on the stock units. If you set your initial timing to around 15 degrees, and disconnect the vacuum advance, the throttle response and pickup is much better. But then you need to limit the vacuum advance if you want to hook it back up.
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Post Fiend
Joined: Nov 2005
Posts: 7,437
Likes: 4
From: Charles Town, W bygod Va
Sounds like I need the kit in ARDWKNTRK's link. Thanks for that, BTW. I've got an edelbrck rv cam performer intake and 1406 (I think) carb on my 351w. I've got the initial timing set at 20deg, and it seems sluggish still. I am not sure what's going on with my advance, according to the 15l markings I have, I should get 30deg mech. advance, since I am only getting 15, I assume that either 1) The heavy spring is so heavy that it wont allow the timing to advance (or it starts advancing at 5k rpm or more), or 2) The light spring is so light that it is advancing 15deg at idle, and the 15deg I am seeing is from the heavier spring....
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