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I have an 83 5.0 timing issue

New User
Posts: 2
Joined: 12/12
Posted: 12/19/12 12:16 AM

well its a 302 5.0 and it has competition cams cam 500 inter. lift 500 and i was wondering what degrees it should be to idle correctly could some one pass over a little advice please  

Post Reply
Posts: 166
Joined: 04/12
Posted: 12/19/12 09:16 AM

set it to stock timing marks... to start with...

one of my books shows the timing on carb models ... 10 before TDC at 700 RPM...

thats the best place.. i am taking that you still have the duraspark distributer with 3 wires..

figuring out a proper mechanical advance curve and then the vacuum advance curve is quite time consuming on an instrumented dyno...  or in a car with detonation sensors in the side of the block..

i could probably type a response in for an hour.. and it still would only explain the theory on how it makes a difference on how much advance you need...

there are some aftermarket distributers with electronic adjustable advance curves .. so you can use a tiny screw driver to change the position of the rotary switch. you can select a slightly different advance curve setting...

on the mechanical advance there are actually 2 stages..
speed at which the mechanical advance starts to move
speed at which the mechanical advance reaches the maximum
total amount of mechanical advance.

on the vacuum advance..
vacuum level at the point it starts moving
vacuum level when it reaches full advance
total advance amount.

and on dual vacuum chamber models.. there is a secondary diaphragm to throw into the calculation..

google this term.      duraspark advance curve       it will take you to a bunch of forum posts..

idle quality is usually controlled by the carb idle circuit.. but i can also spend an hour on properly adjusting the carb...  if you are still there .. there is a forum thread over in mustang monthly on the 4100 carb..  the theory is the same...   do you have a 2150 2 barrel or the 4180 holley 4 bbl HO carb..  i have some good info on both..  

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New User
Posts: 2
Joined: 12/12
Posted: 12/19/12 09:26 AM

well i just bought it and i can tell by idle its off alittle but it has a 4bbl holly it was gonna be for drag but im not goin that far yet  

Post Reply
Posts: 166
Joined: 04/12
Posted: 12/19/12 08:13 PM

set it to 10 degrees and see how it runs first...

use a vacuum gauge to set lean best idle... i can describe that.. if you need..

if  you have a flat spot as you come off idle...   there are ways to fix that also.. and its NOT rejetting the mains in the carb...

idle circuit
idle transition circuit
primary main circuit.

then because you are drag racing.. you are going to have the secondaries open very early and need a well timed accelerator pump discharge amount and time..

the idle transition circuit is important because when you come off idle.. if the idle transition circuit goes lean.. or rich.. you will loose power at that point..  before the mains come in and the car takes off hard...   hence the flat spot..   this may really help with your 60 foot times and your launch..

can you post the number off the air horn of the holley...   LIST - R-12345- 3A..   or an E3ZZ-2356-2A  

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New User
Posts: 7
Joined: 05/13
Posted: 05/30/13 04:56 PM

My 1983 Capri RS will not idle well until you hit 15 degrees with the vacuum advance unhooked and the vacuum port on carb plugged. I have a list 1850 600 cfm holley on mine. This is about the same point where the EFI engines liked to be timed also.  

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