Hey guys, I've got a 10.25 compression 300-4V Skylark, as some of you may know. I want to limit my mechanical advance to 18 degrees crank at about 3000 RPM. With the 2 speed and 2.78 gears, it seems to want a lot of initial. It bogs off the line at lighter throttle then picks up, and nothing I've done with the carb (Edelbrock 600) seems to work. I'm using manifold vacuum advance. I can't just jack up the initial with the stock advance curve because it'll ping. So, after all that, what's the best advance kit to limit my advance? I've got a Mr. Gasket in there but it doesn't limit it more than a few degrees. We're still talking 37 total at 4400 with 10 initial. It runs like a dog on 7.5 initial. PLEASE HELP! Thanks! Aaron
Your problem is most likely having the vac advance connected to manifold vac insead of ported vac. OR, If your car is pinging with only 18 deg (mecanical), then your timing chain or balancer has probably slipped and/or your readings are wrong. Most V8 cars want 36 deg total mechanical at 3K, and you can run 10-12hg of vacuum on top of that. I have an Olds 442 with 400 big-block with 10.5 compression and i'm running 16 deg inital, 36 deg total with 10deg of vac and it runs perfectly. You don't want to run full mainfold vacuum because you're essentially negating the purpose of the vacuum (to give you more advance in low-load high vacuum situations) like cruising, and removing the vac advance under high-load low vacuum situations (like WOT). I've found that running full manifold vac tends to cause problems. You're putting full vaccum advance in even at idle which is not good. If you're running a standard can to mainfold vac, with 7 deg initial, then you're really running 23deg advance at idle!! no wonder you're having problems! First thing to test would be to plug you vaccum advance and vacuum port, set your timing to 36deg at 3000 RPM and let the inital set where it will (it really doesn't matter that much) - then drive the car and see how it runs. My guess is it will run great. If it doesn't ping that way, then the problem is the way you're connecting your vacuum advance, and just get yourself a smaller advance can (stock is 16hg and you want a 10hg or a 12hg can) and connect to ported vaccum and you'll be running like a champ. :grin:
Thanks for the quick reply! I'm still jealous of your cars! After installing the weights and springs in the Mr. Gasket kit...I can now dial up initial...I have room to play with for the total...with 13 initial, I'm now running 33 degrees total...it only pings from low to high shift...I'll be out of town for 10 days, but I'd still appreciate if anybody has anything extra to add...I'm always tinkering with my old cars...sometimes they run worse, sometimes better! p
I disagree. There is nothing wrong with running manifold vacuum to the advance cannister. Under high load, vacuum is low, and vacuum advance goes away leaving you with mechanical and initial. Most stock Buicks run best at 30-34 degrees total. If you bring that advance in quicker, you must limit the vacuum degrees to 8-10* This is best accomplished with an adjustable cannister. Increased initial timing allows the throttle blades to be more closed at idle. Lot's of stock engines used full manifold vacuum. Ported vacuum was used in later applications. I run 16 initial, 32 total, + 10 degrees vacuum. I idle at 26 degrees. Car runs great, with great throttle response. It also runs cooler. There is nothing wrong with doing things the way your trying. Ported and full manifold vacuum will go away at WOT. You just need to limit the mechanical, so you don't overadvance. The easiest way is with a bigger advance stop bushing, or have the distributor recurved. Best of luck.
Well, I got back in town and started fooling around some...and I've got it running 16-17 initial, 35 total, ported vacuum (please don't yell at me Larry p) I'm using a Mr. Gasket weight kit to limit advance and the heavy stock springs because it pings bad with the heavy springs from the kit. It was coming all in before 3000, and the car just didn't like it. With the stock springs, the car feels as lively as I think it will with the 2 speed and highway gears, plus I don't hear any ping even though it's 84 degrees out. The only problem is without the manifold vac it may heat up more when idling in traffic. But it still runs 190 or a little less on the freeway which is what it did before. It seems that I'm running about 45-48 degrees total with vacuum advance, which is OK with me. So, we'll see if it continues running good and how the gas mileage is...Thanks for all the advice...it's good to hear second and third opinions on things when things are running goofy! Aaron
