STRANGE TIMING ISSUES
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Logistics Pro
Joined: Jan 2011
Posts: 4,762
Likes: 54
From: Antelope Valley ,CA
STRANGE TIMING ISSUES
ok so i've been playing with getting the timing right on my 390
here's what i did and found out today
marked my balancer at
tdc
8 btdc
and 30btdc different marks for each location
i checked timing with vacuum advance disconnected
8btdc
i hooked up vacuum advance and checked timing with engine at 3500 rpm
it was wayyyy past 30btdc more like 45-50
so i disconnected vacuum advance and checked timing at 3500 rpm
35-38 btdc
so my vacuum advance is advancing the timing even more than the mechanical advance ?? any help ideas ?
here's what i did and found out today
marked my balancer at
tdc
8 btdc
and 30btdc different marks for each location
i checked timing with vacuum advance disconnected
8btdc
i hooked up vacuum advance and checked timing with engine at 3500 rpm
it was wayyyy past 30btdc more like 45-50
so i disconnected vacuum advance and checked timing at 3500 rpm
35-38 btdc
so my vacuum advance is advancing the timing even more than the mechanical advance ?? any help ideas ?
Laughing Gas
Joined: Jul 2010
Posts: 1,128
Likes: 123
From: Chico, Ca.
Do you have the stock dizzy? 35-38 deg sounds correct for total mechanical advance. You cannot set the timing correctly with the vacuum connected. I don't know if that's too much advance with the vac. Is it running poorly?
Kurt
Kurt
Laughing Gas
Joined: Jul 2010
Posts: 1,128
Likes: 123
From: Chico, Ca.
Kurt
Thread Starter
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Logistics Pro
Joined: Jan 2011
Posts: 4,762
Likes: 54
From: Antelope Valley ,CA
THANKS SLEEPY , so i guess it's normal ,
i have the vacuum plugged into the timed port on the side of the holley carb
mechanical is set to the 15L so 30 +8 = 38
maybe i'll try the 13L and a little more intial
i have the vacuum plugged into the timed port on the side of the holley carb
mechanical is set to the 15L so 30 +8 = 38
maybe i'll try the 13L and a little more intial
Thread Starter
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Logistics Pro
Joined: Jan 2011
Posts: 4,762
Likes: 54
From: Antelope Valley ,CA
port on bottom of carb has 15 iom ( inches of mercury) at idle
timed port on carb has 0 iom at idle and jumps up to 15 iom at 1000 rpm
timed port on carb has 0 iom at idle and jumps up to 15 iom at 1000 rpm
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Post Fiend
Joined: Apr 2008
Posts: 8,261
Likes: 15
From: Big Sky Country
That's what i run on my 390 and it seems very happy, 13L for 26 degrees mechanical + 12 initial for 38 total, the vacuum advance (ported) kicks in an additional 12 degrees, all in by 3,000rpm.
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