383 tuning

[73-charger-383]

having tuning trouble.

it's a 1968 383 that was a 2 barrel car (transplanted into my 73).  I've swapped out the intake for a factory four barrel, added headers, a 600 cfm edelbrock carb, and installed a comp cams 268h which is close to the factory hp cam, 727 with factory 2.73 road gears.

I tried setting the timing with a vacuum gauge - @ idle adjusting for max vacuum and then backing it off 2".  When I do this I'm getting 18" of vacuum, but the car will barely start as it turns over crazy hard (too much advance)....when I set the timing with a light I set @ 16 degree initial, all in @ 3000 rpm, and end up @ 36 ish total.  When I run this, it starts fine, but my vacuum is only at 14 inches.  (all timing changes are done with the distributor advance unhooked/plugged.

When i'm set up like this, if i pull the vacuum line going to the pcv, my vacuum actually jump up to 18" ish inches (by introducing a "leak" the vacuum jumps)... does this mean i'm just crazy rich? 

So --- do i have timing issues, carb issues or both?

[XH29N0G]

I do not have an answer, but I have three questions.  Are all vacuum readings being done at the same RPM?  And do you get a similar behavior opening the idle mixture screws. Is the vacuum advance unhooked when you pull the PCV tube (which I assume you are pulling from the back of the carburetor)?

[c00nhunterjoe]

start at the beginning. What is the 68 motor? How did you degree the cam? What was the initial timing with the 18" reading? What is the problem running it at 16/36 causing you to question 14 vs 18?

[73-charger-383]

not 100% sure i'm following.  It's a 1969 383 out of a c-body (was a 2 barrel). When I installed the cam, I just lined up the crank mark with the cam mark (12 o'clock and 6).  I didn't using the timing gun to check what the initial was with the 18" reading, as to get it started again I had to retard the timing.

I'm questioning it because i've seen a ton of threads saying you should have max vacuum @ idle.  When i'm running it at 16/36, i'm 6" down from where that "should" be. (max 20, backed down two to 18)

The idle mixture screws do change the vacuum, but not as much as i would expect....There's a point where the idle smooths out turning in (richer), but there's also a point where it smooths out leaning it out (and gains two extra inches up to 14")

I'm just at the point where i'm thinking a new carb maybe needed...just want to double check all the boxes before i drop the cash.

[c00nhunterjoe]

The question about the engine was to find out if it is a legitimate origonal 2 bll 383 or it it is rebuilt. A new carb will not change a timing hard start. The cam will affect the vacuum response. I would put a light on it at your 20" reading. I would also verify the crank numbers are correct,  and without pulling it back apart, there is no way of telling how the cam is degreed

[73-charger-383]

finally feel like i've got a bit of it figured out.  I took the distributor cap off to just check everything over as the spark was weak and saw that the reluctor was worn down...I ordered up a replacement, and as i was pulling the old one off, saw that the pin was gone also...I'm guessing it has a lot to do with my tuning issues (i'm kind of surprised it was running at all)..Throwing it back together tonight (and doing the chevy hei module swap)...Should run better with good/consistent spark..