REELAV8R

I had some time while waiting this week for new fuel pump push rod to show up so I decided to mess with the mechanical advance on the distributor.
I have a Mr gasket kit that I bought when I was still running the original engine and had used it to re-curve the ignition. The only components I used were the springs. It comes with three different strength springs colored black gold and silver. The black ones are very weak and could not be used together. One can be used in conjunction with a stronger spring only or you'll have full advance just above idle.
On my rebuild I decided to try the gold and silver together. One of each. I noticed that in this combo there is almost no tension on the springs and the weights do not return to full retracted position. So then the timing would be free to advance several degrees at a very low rpm until some tension is on the spring and it starts to do it's job by holding back the timing until higher rpms. The weights would also be free to fluctuate until rpm got high enough to apply tension to the springs. Neither situation is desirable. It would make timing at idle erratic at best and cause rpm fluctuations.
The only way to combat this is to use only one or the other of the siver or gold and put a stock spring or one of the very weak springs on the other side. These at least have tension on them in the fully retracted position. I settled on one stock and one very weak spring for my combo. Haven't run it again yet to see where full advance comes in. At least it will be stable at idle this way.

I also notice that the weights and center piece do not allow as much mechanical advance as the stock set up. Stock is about 20* the Mr gasket is something less. Didn't/couldn't run it so I don't know how much, but I could manipulate it and clearly see that it advanced less.
This would mean more intial timing if you want to get that 34* to 36* all in timing less vacuum.
I also tried the mr gasket weights with the stock center piece. This does not work as the weights interfere with each other and if one advances prior to the other it hangs up on the other weight.

So basically there is almost nothing in the kit that will work for this engine. The stock engine didn't seem to care about the unstable weights at idle and the springs worked to re-curve the timing. This one is much more sensitive (greater overlap) and will not tolerate the sloppiness of the springs.

cv67

Had the same experience with an MSD curve kit no matter what I tried couldnt get the motor to "run".

Wound up sending it to this Bob Jennings Dyno Shop in North Hills ca
$80 and the car ran the way it was supposed to, night and day
Let him do his own tweaking on it. Says most those bushings are not accurate nor the springs any good. Worth it.

7T1vette

Most likely, the advance plate in your distributor was binding and causing an excessive load that those springs could not overcome. Either that, or your distributor was not a GM brand distributor for which those springs were designed.

Are you sure that Mr. Gasket kit was correct for your distributor?

REELAV8R

That's a good point. I did have some binding last year due to dried out grease on the shaft of the mechanical advance. But that has been fixed for quite a while now. It advances and retards freely.

It is the original GM HEI distributor. I thought maybe there was a problem with it initially as well. I pulled out my GM HEI for the 400 I have and same issue on that one with the springs. Both are stock units from the 70's.
Fact is the springs are just a little too long. Maybe only 1/8 inch or less but they need to be slightly shorter just so some tension is on the pins to keep the timing fully retracted until RPM's start to advance the timing by stretching the springs and not by taking up slack.

resdoggie

Threw my Mr Gasket kit in the garbage where it belongs for the same reasons you mentioned. My original HEI distributor was inspected and a new composite gear put on during my retro roller install. But here's something interesting. I looked up the specs from the FSM for my '76 L-82 non-California dist'r. Seems the GM engineeers of the day had this 36* advance cased back then and probably a lot earlier than that. With the original weights and springs re-installed, my mech'l advance can be set to all in by 3000 rpm. Also, the original vacuum can comes in at 8* or 10* with a total of 12*. So, for my setup, I'm using the original HEI dist'r with an MSD HEI upgrade kit set to 34* and with vacuum, 48* total. This is considered near optimum by many expert tuners for my build with hyper pistons and AFR 195's. I will guess that this "optimum" is about 95% or better for peak performance. And that's good enough for me.

1977L48

if you have a large cam, ie choppy idle, the springs will make your idle unstable, meaning you will set your idle, give it some gas, and it will not return to your idle due to the weights advancing and your vacuum advance kicking it. ive always had great luck with the mr gasket curve kit, on basically stock engines because of the small cam and low compression ratio