VetteRed1965

My advance starts to come in at 1200, I have one black and one silver spring. What are the ratings on the spring from light to heavy.

65tripleblack

How would that help you? What are you trying to accomplish?

66since71

I can't confirm the color codes, but you can rate them by counting coils from stiffest (fewest coils) to softest (most coils). If there's a difference, thicker spring wire is also stiffer.

Harry

VetteRed1965

Hey Triple, I have the timing all in at 2500 at 36 mechanical,15 at initial. Now my advance starts to move just above idle.Gives an irractic idle. Jumps around between 850 to 1000 rpm's.If I has stiffer springs would this calm it down or It might just be my cam.

This thing now runs like a scalded ape . Thanks for all the help.

VetteRed1965

Harry, Thanks for the info. I'm a newbie at this timing thing. But its not tough once I stopped thinking it .
Now that I have the vaccum advance hooked up. The car runs smoother all the way to red line and pulls great thru the powerband.
Lars knows his stuff ! Now trying different spring rates...

65tripleblack

Tie the weights with a rubber band and recheck. If the idle is rock steady then you've found the cause.

DansYellow66

If your timing marks are jumping around at idle with a timing light then you centrifugal (mechanical) then the most likely cause is the springs are too light and it's starting to advance at idle. The rubber band idea would work well for a check.

Plasticman

I have also found some cheap aftermarket springs too long. If they are loose when installed, I toss them.

I use a small pull (fish) scale to "rate" my springs ("X" wgt. @ "X" length).

Plasticman

VetteRed1965

Tied the weights, now to find stiffer springs. I will try and bend one coil down then cut...

Tiros

I don't have any problems with some advance at idle. You need light springs so that it all comes in on time. The initial, doesn't really matter either. When you get it timed by max advance @ rpm, the initial can just fall where it may.

So with light springs advance at idle is not a problem in fact it is expected! I suspect your "hunting" problem is not related to the springs.

How much vacuum do you have?
What vacuum can are you using?
What idle can you get with the can attached?

What size engine? What size carb?
Is it a Holley DP? Uncovering the power valve at idle?

DansYellow66

It will matter if you are trying to get a decent and stable idle so you can drive the car on the street. With a cam and weights wiggling around at idle because of light springs, trying to set your idle by vacuum and timing is a a joke. Yeah, you can power time it at max advance - but if the avance is jumping around at idle it's most likely going to idle like crap and be more difficult to drive off at slow speed without bucking.

VetteRed1965

I ended up cutting down a few springs to get it stable. Since the advance starts to move about 1200 rpm's. Its great to have a forum like this. Thanks for all the help .

Tiros

I am still not clear on why the advance would be jumping around due to the springs. The weights should attain equilibrium for any given throttle /idle/rpm setting. Why would they continue to move after that point?

Now if the the engine speed were changing due to some other issue, say a vac leak, carb problem etc, for sure the mark will be jumping around as rpm is varying and the weights are moving.

fwiw I have 2 lightest springs available installed. I am for sure in to the advance curve at idle. No surging, hunting, or poor throttle response. Furthermore I can use any of the springs I want, and still obtain the same steady idle rpm. (even with springs weak enough to allow advance at idle rpm)

@the OP:
Glad you got it sorted, but the heavier springs will (generally) kill your performance. I think you have another problem.

JohnZ

That's called "dithering", and it's caused by having a vacuum advance can that isn't properly spec'd for the level of idle vacuum being generated by the engine. That's why the vacuum advance can spec for being fully deployed should always be at least 2" Hg. less than the engine's idle vacuum, so the advance can (connected to full manifold vacuum, not "ported" vacuum) remains solidly deployed against the stop at idle. If the vacuum advance can doesn't meet the 2-inch rule, it will "dither" between fully and partially deployed at idle, which will make idle rpm unstable, which will make the centrifugal advance unstable.

This article explains how the vacuum and centrifugal advance systems work together for peak driveability and performance:

http://www.camaros.org/pdf/timing101.pdf

VetteRed1965

Got it ! I bought an accel adjustable can. My vaccum at idle is 9. So I need to set the can to release below 7 hg. Which is 4 turns in on the adjustable vac can .

Tiros

So dithering isn't caused by light springs, its the wrong can.

@the op:
Don't get the adjustable, the spring adjustment changes the rate, many people use it to limit the max advance, but its just not optimum. So then you have to add the limit piece, and you limited already with spring adjustment, so you wind up with less range.

Get yourself a #236 can, VC-1810 or I think its also called a B28. Its 0 degrees at 4", and 16 degrees at 7". Seems perfect for your 9" idle, and you wont have to mess with it at all. After that do try the light springs again and let us know how it went.

Read and reread Johnz link.
And this is the rest of the story
http://www.corvette-restoration.com/...c_Adv_Spec.pdf

VetteRed1965

Starting to make sense...Not reading your post until I installed a VC1765 B26 5-7 8 @ 11-13

I think your find is better suited...

Tiros

I think the one you have won't work too well with only 9".
I got my 1810 at autozone for $12.00