CarburetorsCarb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
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The Vacuum advance is on ported vacuum from the carb.
I set the timing to 32 degrees max @ 3100rpm and that landed the base timing to 14 degrees. When my engine is idling it's a steady 14 degrees, as soon as throttle is applied the timing gets momentarily retard to around 5 degrees before advancing like normal.
Check out this vid to watch what it's doing exactly:
It will do this with or without the vacuum advance hooked up, and I think it's giving me my stumble/hesitation right off idle that I've been accusing the carb of doing.
Re: Ignition timing retards before advancing from an idle... any ideas?
Yes, timing was set to 32 degrees max @ 3000-3100rpm without the vacuum advance hooked up. But the dist will pull timing like this with or without the advance hooked up.
Summit agreed there is a defect and they are sending me a new dist now.
I'm thinking of trying something when the new dist arrives. I will set it to a mechanical max of 32-34 degrees all in around 2800-2900rpm with a base around 12-14 but I will use a 15 (crank degree) vacuum advance @ 8" vac hooked into the manifold vacuum port on the carb.
This should give a base idle timing of 27-29 degrees and a cruise timing of 47-49 degrees. So we'll see what happens. Alot of the Ol' Timer hot rodders, engine builders & drag racers are using manifold vacuum for their advances. (with a lumpy cam & high compression) And it is suppose to yield a smoother idle, cooler engine temps @ idle, less idle fuel from the carb, more throttle response, less unburned fuel.
But not always, some engine combos react better to ported vacuum. So this will just be a test.
Re: Ignition timing retards before advancing from an idle... any ideas?
Quote:
Originally Posted by Mykk
Yes, timing was set to 32 degrees max @ 3000-3100rpm without the vacuum advance hooked up. But the dist will pull timing like this with or without the advance hooked up.
Summit agreed there is a defect and they are sending me a new dist now.
I'm thinking of trying something when the new dist arrives. I will set it to a mechanical max of 32-34 degrees all in around 2800-2900rpm with a base around 12-14 but I will use a 15 (crank degree) vacuum advance @ 8" vac hooked into the manifold vacuum port on the carb.
This should give a base idle timing of 27-29 degrees and a cruise timing of 47-49 degrees. So we'll see what happens. Alot of the Ol' Timer hot rodders, engine builders & drag racers are using manifold vacuum for their advances. (with a lumpy cam & high compression) And it is suppose to yield a smoother idle, cooler engine temps @ idle, less idle fuel from the carb, more throttle response, less unburned fuel.
But not always, some engine combos react better to ported vacuum. So this will just be a test.
Ported Vacuum is an emissions era crutch, nothing more. Engines respond best to Manifold vacuum as long as the rest of the timing is on. Some cams may want as much as 30-34* of idle timing.
Re: Ignition timing retards before advancing from an idle... any ideas?
I didnt get to watch the whole video, but I did notice that you are using a timing gun with a digital dial back.
I had this exact same problem and it bugged the crap out of me for a long time.
You cannot use that style timing light with the MSD6A box. I talked to several MSD tech guys and they all told me the same thing. Cannot use a dial back/ digital timing light. I was using a snap on gun and had to borrow a friends gun that was probably 20 years old.
If you want verification of this call up MSD they will tell you.
