Distributor recurve springs
 

Hey guys I was having a problem with my truck it did not have power on take off from a stop,so rebuilt the carb problem still there, It ended bean the vacuum advance so I took the distributor out and exchange for another sense it's lifetime warranty, long story short had to go thru 3 distributor because mechanical total timing to high finally got one with the L13/l18.Now here I go with the question about the springs,how do they work, do the softer springs allow total timing at lower rpms,or the stiffer spring allow timing at lower rpms, please help me understand this thing about the springs so I can recuve my distributor.
I have one set of each soft, medium and stiff springs. thank's in advance.

TASBOJ.......

The softer springs allow earlier advance. But initial power on takeoff is mostly related to the initial timing. I run my 460 at about 18 deg BTDC. Just keep bumping it up a couple of degrees at a time and see how it drives.

Thank's Turbo Dog for the quick response,my disy is set with stiff springs at L13 which gives me 26* mechanical total timing and my initial at 10*BTDC = 36*,This is my problem if I'm driving @50 mph and I step on the gas my engine pings,I thought the total timing should be in by then @ those rpms, and no matter if I drop my initial to 5* or 2*BTDC it still pings @ this speed.If I'm at a light and try to stomp on the gas it pings isin't the stiff spring suppose to delay the mechanical timing on take of I'm stump any advice Thank's

TASBOJ

Hey Tas. Bad gas can cause this. You didn't happen to fill up your gas tank just prior to this ,did ya?

Hi JEFFFAFA I always put gas in the same gas station never had a problem with their gas,I fill up with 89 octane. this pinging thing all stared wen I changed the disy, do you think it could be the vacuum advance pulling to much.

Just spit balling, but is your vacuum advance connected correctly to ported vacuum and initial timing set with vacuum advance disconnected and plugged at carb? Not familiar with the Mallory Unilite if that is what you are running as posted in sig line.

gfw1985 yes my vacuum is ported, and timing set with vacuum disconnected,I am running a pertronic ignator now I will change that on my signature.
I think the vacuum advance myth be pulling to much,some of them have a number stamped on them for the degrees they pull, does anybody know which one I need for my set up.

TASBOJ...

First things first - vacuum advance will not cause any problems related to acceleration from a dead stop. Notice racing engines don't even have vacuum advance, and they do pretty well off the line. Vacuum advance is for economy and driveability tooling around - it is completely unrelated and distinct from mechanical advance. Lighter springs means mechanical advance comes in at an earlier RPM than stock. Limiting the total advance via the slot means the initial crank timing can be advanced much farther than would be the case otherwise. This will make for a lot better off idle acceleration.

Vacuum advance is likely the problem with pinging at part throttle acceleration or under load going up a hill for example. Remember there are three components to engine timing advance - initial (crank) timing, mechanical advance (springs, weights, slot) and vacuum. The mechanical is RPM only, the vacuum is load dependent.

It sounds to me like you don't have the initial and mechanical where you want it, and you need a light to be sure - and too much vacuum advance at highway cruise speeds. It sounds like 18 slot is used (not 13L) that's 36 degrees "total" mechanical plus your initial. That's putting you a bit too far.

Get your mechanical setup where you want it, and the vac won't be a problem at cruise. Modern vac cans are adjustable for the amount of advance with a 3/32 or 2.5 mm allen wrench. Try fully clockwise (about 12 turns) to start and then back off a couple turns at a time till there is no pinging at cruise and part throttle acceleration. Pinging with full throttle acceleration from a dead stop is caused by too much crank (initial) timing.

The best way to be sure, get some timing tape or mark your damper out to 40 deg BTDC. Disconnect and plug vacuum advance. Using a timing light and a tach you can watch the timing at idle, that should be your initial. As RPM increases the mechanical will come in. This should be limited to about 36 or 38 degrees, by 2800 to 3000 RPM you can play around with the initial till you achieve this figure, it is dependent on the advance slot in the breaker as you've discovered. The vacuum advance will add around another 10 degrees on top of this by the time engine vacuum comes back up - steady cruise, part throttle. This is close to 50 degrees BTDC, but remember too modern gasoline and high compression don't get along very well. You will likely have to back off a bit on the initial unless you're running the good stuff. Hope this helps.