First I’ll give you the engine specs. 383 cid, 9.8:1 compression, AFR 195 street eliminators 76cc chambers, QFT Slayer 750cfm (8.5” power valve) with the transfer slot at .020” exposure (adjusting idle speed with 2ndry butterflies), Edelbrock RPM AG. Camshaft specs: Howard’s cams 180885-10 - hydraulic roller 278/278 @.006, 225/225 @.050, .525”/.525” lift (I’m using 1.6 rockers so .560/.560” lift) and 110* LSA installed 4* advanced. Initial timing is 14*, getting 38* with the vac advance plugged into manifold vac. I’m getting 15”Hg@900 rpm in neutral with a 13.5:1 afr. It doesn’t like to be any leaner. Trans is a TH350 w/ a 2k stall. I’m using an AEM wideband installed in the DS collector to monitor afr’s.

So the problem is it won’t idle in gear. As soon as I drop into R or 3 the rpm drops to around 500, vacuum at 5”Hg and within seconds dies if I don’t gas it. The only way I’ve gotten it to idle in gear is to richen it up to 12:1 and no load idle at 1100rpm. That only gets it to idle like $#!+ @600rpm though. Vacuum is relatively steady just changing with idle rpm fluctuations. I’ve checked for and eliminated any vacuum leaks save for the PCV (no inline restrictor) which is plugged into the 3/8” brake booster port along with the booster and vacuum modulator. There isn’t a PCV port on the front like my old Holley SA. I’ve checked both of those and no leaks using a mighty vac to pull 15” and watching for vacuum to drop. So now I’m stumped because I’ve checked everything I can think of and this baby cam and average carb just won’t get along. I need suggestions from the dudes who have done this longer and more successfully than I have... I’m new to it so not a huge requirement. She’s also running kinda hot, around 200* with the fan running and a 180* stat in it. I attribute that to it being a new engine and straight distilled water until I ensure no coolant leaks but I’d like to know if something about that is telling or odd too. I’m using a champion 3-row rad and 16” e fan.

Im not ready to use Sofa’s guide yet as the car won’t idle in gear and therefore doesn’t drive. There’s something beyond that going on right now, it shouldn’t be dropping that much rpm going into gear.

Initial timing is is right there in your quote, 14*. My problem with advancing it much more is my total with mechanical advance shouldn’t go much over 32-34 since these heads are supposed to have fast burn style chambers. Maybe my thinking on this is a little wrong. I can’t limit my overall timing since this is a stock style non CC HEI distributor. It’s one of those Skip White units, works great.

Did some more tweaking tonight, little by little I’m getting somewhere. I bumped up timing to 18* initial which helped enough for me to watch the afr in gear at idle. It’s leaning way out before it dies so I backed the idle mixture screws out 1/8 turn at a time until I had a decent ratio at idle in gear, 13.4-14.0. Problem is it’s at an eye burning 12.1-12.5:1 when not in gear. It’s still dropping way down in rpm, about 400 rpm, and tries to lean out and stutter but recovers. Still seems like too big of a drop in rpm even if I’m up against the converter a little bit (it does seem pretty tight for a 2k). Is this normal behavior for a noticeably-larger-than-stock cam at idle? I’m thinking this more of a timing issue than a carburetor tune issue now.

I’m able to monitor my afr’s at idle and it isn’t getting overly rich, it’s leaning out when in gear. So that’s not the problem.

As I’ve read more about what I’m experiencing I’m seeing that, as someone mentioned above, when I place it in gear the load reduces idle rpm, vacuum drops and since I’m using manifold vacuum to advance my timing at idle so does my advance. That means I get double whammied into a slow, sluggish idle. So the only way it seems to combat this is to increase my initial timing, limit overall timing somehow, and see if it won’t idle acceptably hooked up to port vacuum. I went with what I considered to be a small cam for the engine to avoid all this trouble. Really don’t want to have to buy another, much more expensive distributor just to get that tuning function (mechanical advance limiting).