Got a recurve kit with weights, 3 sets of springs, and 3 what look like bushings? Now how do I aplly this kit to my GS? Its a '69 GS 350 with a TA 212 cam, Edelbrock 750, and stock everything else. The distributor is new (reman I guess) from local parts store with the Pertronix conversion. Which set of springs should I use? Do I need to change the weights? Thanks, DB
Someone else can answer this better than I, but when you're swapping parts and checking things out, just be sure the advance isn't kicking in at idle. With the right weight/spring combo that can happen easily. Which really makes things crazy.
DB, I can't tell you the desired curve for a 350 but in general: This is ALL done with vacuum disconnected and the port on the carb plugged. The bushings regulate the mechanical advance. For instance, say you have 12 degrees initial and want a TOTAL of 30. You need a bushing that will allow only 18 degrees MECHANICAL. So that's 12 initial + 18 mechanical for a total of 30. Bigger bushings = less mechanical available. The springs and weights determine the RATE of Advance.. that is, how quickly and at what RPM the mechanical advance begins and ends. For example, on a big block Buick a ballpark is 14 initial and 34 total "all in" by 2500rpm. So you need a tachometer. If your tach is in the dash (as opposed to on your timing light) you'll need someone to watch it while you operate the throttle and watch the timing light and marks. With the engine at operating temperature - with your timing light set initial to 12 degrees at idle (rule of thumb is to use as much initial as possible without causing detonation/ping). Another popular way to set initial timing is with a vacuum gauge (you should get one). Connect the gauge to an unported manifold vacuum source (usually on the bottom of the carb) and advance the distributor timing for maximum vacuum. If your timing light is a dial-back you can check total. If the 350 and 455 have the same diameter (circumference) crank damper you can mark the damper at 1.75" clockwise which = 30 degrees. Then you don't need a dial-back light.. the new 30 degree mark will line up with the factory timing tab and you just add whatever that reads to 30 for your total. Check the circumference (or someone can tell us) then divide by 360 degrees, multiply by 30. For example, if your crank damper is 15" circumference divided by 360 = .00416" x 30 (degrees) = 1.25". It's handy even if your timing light is dial-back.. good for checking with both methods. Take the throttle up until the advance stops going up. Hold the throttle at that point and check the RPM. Lighter springs will bring the total in quicker (lower RPM), heavier = later/higher RPM. You probably want it all in between 2000-2500rpm. Change springs as required. Initial Advance is at idle. Mechanical advance is what's "built" into the distributor.. curve. Total Advance is Initial + Mechanical. With vacuum advance connected you'll probably see 40+ degrees... this is NOT Total advance.. don't let anyone tell you it is. There are adjustable vacuum canisters out there if you choose to keep the vacuum option. Vacuum advance is used to maximize fuel economy at cruise, not for performance. Think about it.. when at WOT vacuum goes away as will the advance that goes with it. So at WOT you'll only be using the TOTAL of 30 degrees or so. When at cruise RPM vacuum will be at max as will timing, which helps economy.
