MILO

I've been trying to dial in my total mech advance at 36 deg but can only get 20-24 deg. I read the Lars paper, not applicable for HEIs and some other papers from other Chevy performance forums. Stock h-balancer correctly lines up as I verified TDC at 0 deg.

Base/intial timing at the h-balancer is 12 deg. With an advance curve kit with the lightest springs, I can only get up 20-23 deg with my adjustable timing light with the H-balancer lining up with 0, RPMs at 4000.

Now I read, actually on another forum, that a stock HEI is only adjustable up to 20 degrees because of emission concerns. Does this mean I need an after market HEI or am I missing something here?

BSeery

Make sure that the weights are not binding up and that the advance plate can make full movement. I had one that was stuck before and would not advance more than about 10 degrees.

MILO

Thanks for the suggestion but the weights are not binding, the whole advance shaft moves freely. You think I should diassemble the dist and lube everything? Or are these stock HEIs limited to how much advance you can get?

page62

I'm confused. Why isn't Lars timing paper applicable to HEIs? I personally watched him time my car using his method. Are you adjusting timing at high rpm, like you're supposed to? You should be able to turn the distributor more than far enough to get this amount of advance dialed in.

FYI: Initial timing should not matter.

Twin_Turbo

How much initial are you running? the mechanical advance is mechanically limited to about 20 degrees so if you're aiming for 36 set initial to 16. You can also get a new center plate or modify the original to allow more max. mech. timing. The shape of the plate determines the advance rate (combined with springs & wieghts) & the max. amount of mech. advance.
The stock springs are heavy so the timing comes in pretty slow
You can not run the stock vac advance with this setting though since it will add too many vac. degrees on top of the 36.

Fevre

Directly from the Lar's bible, the book of dist:

NOTE: This procedure cannot be used on the HEI ignition systems. Removal of the springs will cause an artificially over-advanced condition that will never be achieved with the springs in place. You can use the basic technique described in this paper with the HEI units (setting timing up to 36 degrees), but to check total timing, you must install a set of soft springs. You cannot remove the springs altogether. With the soft springs in place, rev the engine until the centrifugal advance is pegged out. Adjust for 36 degrees total. Then re-install your original springs.

page62

Oops, my bad. I was thinking of his procedure from the advance curve kit: install his springs then measure total timing (without vac advance) at 3500 rpm.

In any case, with a set of soft springs from a recurve kit there's no reason why it wouldn't be possible to dial in 36 degrees at 3500 rpm.

MILO

Thanks for the input. There must be something wrong with the distributor. Without vacuum advance and the lightest spring installed and initial timing at 12 degrees all I can get at 4000 rpms is 20-23 degrees on the balancer lined up at the zero mark. So 23 minus 12 equates to the distributor advance curve is only allowing 11 degrees?? I'll have to compare the weights and center plate with other advance kits. The one I bought was packaged by Spectre? found at AutoZone. Advance Auto were out of the Mr. Gasket brand but if I remember correctly they look like what I have.

isosceles

I am thinking of a few things that could be wrong.
1. The mechanical advance is binding.
2. the weights are on backwards.
3. dist is installed off one tooth? (not sure about this one)
4. inaccurate timing light?

Even if the stock HEI is only adjustable to 20 degrees, with the added mechanical advance you should be able to exeed 40 total. On my 79, getting 36 degrees in by 3000 rpm give me about 10-12 at idle. If I set it to 20 at idle, I would end up with 40+ total mechanical.