Where to set timming 0n 86
01-11-2013, 09:33 PM
#1
Thread Starter
Join Date: Dec 2012
Location: oklahoma
Posts: 15
Where to set timming 0n 86
HI , can anybody tell me what degree of advance i should be running on my timing , and also if should be using port or full manifold vacuum for my vacuum advance on my distr. Im running a 86 302 ho bored .30 with stock crank and rods , e cam trick flow springs on stock heads , mallory hei distr 8500 series i think and carbed , took the efi off when i built it , i just cant seem to get it down just right , i believe its set at 17 initial , thanks .
01-12-2013, 07:20 AM
#3
5th Gear Member
Join Date: Jul 2012
Location: ohio
Posts: 3,628
Initial timing should be set at 10 to start with using manifold vacuum.
You can bump it up a degree at a time until you start to get pinging or rattling, youll need to do a test drive after each new setting. then reduce it a degree. You want manifold vacuum because at idle your mix is lean and needs to be lit sooner. As you accelerate the mix richens and the rpms come up the vacuum advance drops off and the mechanical or centrifugal advance starts to take over. at wot there is no vacuum advance and is all purely mechanical.
You can bump it up a degree at a time until you start to get pinging or rattling, youll need to do a test drive after each new setting. then reduce it a degree. You want manifold vacuum because at idle your mix is lean and needs to be lit sooner. As you accelerate the mix richens and the rpms come up the vacuum advance drops off and the mechanical or centrifugal advance starts to take over. at wot there is no vacuum advance and is all purely mechanical.
01-12-2013, 01:12 PM
#4
Thread Starter
Join Date: Dec 2012
Location: oklahoma
Posts: 15
I went out and checked it and it wasnt even at 0 ,WOW , i know i set it when i first got it running , i have been chasing a carb problem so i havent fooled with it but im amazed that it would even start or run at all like that , its now set at 13 and it seems to like it and idles really good so do i really need to use manifold vacuum for the advance ? Also should total be about 34-37 .
01-12-2013, 01:51 PM
#5
5th Gear Member
Join Date: Jul 2012
Location: ohio
Posts: 3,628
You can use ported vacuum but it kind of defeats the purpose having a vacuum advance , you want the vacuum advance at idle and gradually fall off as the throttle plate is open and the mechanical advance starts to take over.
Manifold vacuum advance give you a crisper throttle response off idle. Depending on the advance curve of the centrifugal advance your mechanical timing is all in some where between 2500 and 3500 rpm, so your vacuum advance does nothing. This is why we want the manifold vacuum advance , so that your advance is high off idle and then as you open the throttle the vacuum drops off and the switch between vacuum and mechanical is almost seemless.
Manifold vacuum advance give you a crisper throttle response off idle. Depending on the advance curve of the centrifugal advance your mechanical timing is all in some where between 2500 and 3500 rpm, so your vacuum advance does nothing. This is why we want the manifold vacuum advance , so that your advance is high off idle and then as you open the throttle the vacuum drops off and the switch between vacuum and mechanical is almost seemless.
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