I wish my car was fuel injected.

Anyway, I can't get enough machanical advance out of the damn thing. I was wondering why my new Vortec 350 ran great except at WOT. I can only get 12 degrees of mechanical advance out of it. I opened the slots that limit total advance, making sure nothing was binding. Then I replaced all the weights and springs with the lighter springs and proper bushings, and tuned it up with a new cap and rotor. Well, it's better than 5. I ended up stretching the light springs :nono: so I had to put the medium springs in, which is what's in there now. You can feel the timing kick in, but stop at 2000 or so. What it looks like is it needs a couple longer light springs. Anybody go through this PITA with a stock HEI distributor? Is there some kind of stopper of some sort prohibiting further advance, or something else? I already made sure the vacuum portion works properly(and will be replaced by an adjustable unit), and everything works freely as it should. Still no more than 12. What confuses me is the rotor moves far more than that when you twist it, installed in the motor, simulating mechanical advance. I'm confused Anydoby know what's going on?

 

I had read somewhere that the stock HEI mechanical advance maxxed out at 20 degrees of advance. I had problems with a Mr. Gasket recurve kit (don't do it!) limiting advance due to mechanical interference, but better luck with factory stuff.

Is it possible that the weights are sticking slightly advanced at idle and only giving you 5 or 10 degrees from there? The soft springs have done that to me.

 

Sounds like Something is messed up.
The advance weights or centerpiece is not intalled right
or something is causing them to bind, preventing full advance.

What is the number stamped on the distributor housing?
You could allways go to the wreckers and get another distributor
out of a carbed car. Most have 20 to 24* mechanical advance.

I find the lightest springs in the advance curve kits are way too light. They cause the timing at idle to be all over the place.
The timing is already advanceing at idle.
I use 1 med spring and 1 light spring. This allows plenty quick advance and stable idle timing. Try it.

 

Now that I think of it, don't the 2 heavier springs restrict timing to around 10-12 degrees?

And yes, I also noticed the light springs were a bit light at idle. Any idle over 600 RPM would cause idle speed to jump due to ignition advance, making engine idle speed between 600-1000 RPM impossible.

I even tried to slightly shorten the light springs to tighten them up at idle slightly. Didn't work.

Theoretically the 1 light spring/1 med. spring would work. But wouldn't that med. spring limit total mechanical advance?

And I checked again, everything is free in the distributor. I had it out a dozen times and even tore it down. Had the cap off 20+ times.

 

"Theoretically the 1 light spring/1 med. spring would work. But wouldn't that med. spring limit total mechanical advance? "


Nope , try it. Your putting way too much thought and theory
into this. Get a advance timing light and play with the different combinations of springs. Seems the best overall street performance is not all in by 2500, but and nice smooth advance curve that ends between 3000 and 3500 or so.

Total mech adv should be 32 to 36 deg with 12 to 16 initial.
Cruise vacuum advance will range betwwen 10 and 20 deg at high vacuum. This varies from motor to motor.

 

You don't have the shaped centre plate (the one that the weights work against) in upside down by chance do you?

I tried that and it will definitely limit the advance!

I think it worked better than the Mr. Gasket kit...

 

Nope, it's in there right. So is everything else. And I still won't get more than 12 degrees. I did take a close look at the directions, and the curves they show say one set of springs maxes out at 8 degrees or so, one a little over 10, and the lights at about 20. I guess I ought to try the light springs again, for the sixth time. If it weren't for the light springs being so light that they'd advance at idle, I'd stick with them. Anybody have any ideas about keeping that from happening?

BTW< I opened the advance slots in the distributor, filed everything, even lubed the weight pads and ground down the center plate slightly. I should have plenty of room for advance, so might there be anything else to get more advance out of it, if swapping to the lighter springs doesn't work?

If they don't work, I'm going back with a mixed set.

 

I gather you're using aftermarket springs from the fact that you refer to directions and curves to look at.

I was experiencing just what you are when I used Mr. Gasket weights because they interfered with the rotor, but only once the rotor was tightened down. I was having the same results, about 8 or so degrees of advance, then it just stops hard.

I started clearancing the rotor with a Dremel and grinding parts left and right before I just hauled the Mr. Gasket junk out and went back to factory weights. Their weights were too long, IIRC.

At the time I lived in a small town where you could freely roam the dump so I attacked a few HEI distributors for the weights, springs, modules, whatever. I found some weights that were almost twice as thick as the ones I was working with and had good luck with them.

 

The weights control how much advance is in the distributor. The springs control the rate of advance. Heavier springs may control full advance to 4000 rpm while light springs may control full advance to 2500 rpm.

Use the lighter springs to check the advance since the engine will be at full advance at a lower rpm (2000+). You can mix and match the springs to control the min rpm wanted for full advance. You can also mix and match the weights and the center cam to control the max total advance.

 

The springs don't "max out". They continue to stretch as RPMs increase. You're reading something wrong. The weights and the cam they work against are what "maxes out", when the weights have swung out to the point that thethey can no longer rotate the cam any farther.

The way to keep the 2 light springs from affecting your idle, is to use something else. Don't bother trying them, the springs aren't the problem, and the light springs aren't the solution.

The combo I've always used is either the 2 medium springs, or one med and one light. Depends on the car and motor. 2 light springs will usually not even retract the thing all the way to base timing.

Have you even tried flipping the cam upside down from the way it is now? Also, have you checked to make sure the bottom of the rotor isn't interfering with the weights?

They do also make different cams for different applications, that allow different amounts of centrifugal advance; this is why I don't trust just any junkyard distributor, because some of them are set up to run like tractor motors.

 

Bottom of the rotor is not interfering, I checked movement with the rotor in place. I also tried the centerpiece upside down. No-go. I checked EVERYTHING I could think of. And the chart I was looking at was a graph of the rate of advance at a particular engine speed. It would take like 10,000 RPM to get more advance out of the medium springs. If anything's wrong it's the graph. Because at 6000 RPM which is my rev limit, the limits are as I posted, with the timing coming in at different speeds. No flame intended.

Still can't figure it out. Im going to check to see what the mechanical timing is like on my C-10. I may need to borrow some distributor numbers and order a replacement.