I read all the stickies about timing and so after replacing the plugs and plug wires, thought I'd give the timing a go.

I will admit that the Vette has a very cheap after market HEI unit on it but it seems to be running well but now Im confused and a little worried.

Got my timing light out, disconnected and plugged the vac advance, set the light at 36 degrees and shot the balancer. The timing light was off a little ( was actually at 32 degrees ) so gave the distributor a little twist and got her bang on 36 degrees by 3150rpm

Hooked everything back up and went for a quick drive. Seemed more responsive and thought all was good.

Came home and decided to check where my initial was etc.
Disconnected vac advance and plugged it. Checked again and was all in 36 degrees by 3100.
Checked initial and found it was 17 degrees.

When I hooked up the vac can again, the timing at idle went up to 41 degrees.

Now this is where I am confused.....
36 degrees - 17 degrees = 19 degrees mechanical.
41 degrees - 17 degrees = 24 degrees vacuum.
Initial = 17 degrees.

Total 19 +24 + 17 = 60 Degrees

As I said, the car seemed to be running OK but looking at all the other posts, 52 degrees seems to be the maximum.

Have I got it right or wrong and what can I do to limit my timing to 52 if indeed it is at 60.

 

your can is producing too much vacuum, believe the stickies recommend the correct cans that give less advance

 

So I need one that will pull about 16 degrees?

 

Is the engine pinging?

 

Doesnt seem to be, not that we can notice anyway!

 

I think what the OP is getting at, is that if he has measured his timing correctly, he's at 60 degrees of advance while cruising, and the car runs fine, which should not be the case.

Remember, you have to be above 3150 rpm for all of your advance (mech and vac combined) to come into play, which means you'd have to be out on the highway running fairly fast.

Scott

 

If you want to eliminate 8* of travel out of 24* total, take the vac can off first.
Mark where the actuating starts then use some vac hose and suck the rod full travel, mark it, or it will be the phisical stop of travel in the channel rod travels in.
Divide the total movement between your two marks into three equal sections.
You want to restrict the last third of movement of the actuating rod.
Figure a way to do that and you got a 16* vac advance can instead of 24*.

I used a little weld in the channel and then ground it with a Dremel to get exact travel I wanted.

 

Many hi-perf distributors have an adjustable vacuum can. Mine came with a small Allen wrench that is inserted in the hose nipple to adjust the total vacuum. I'm not 100% sure how it works yet, but I will be trying in a few days.

 

When you plugged the vacuum advance line back in, did the idle increase?

If it did, it may have started to take on some mechanical advance as well.

 

Had a similar issue recently. I have the B28 can which pulls in 8 dist degrees = 16 crankshaft degrees when fully acutated. Per Lars this is to much for modern fuels. Per his instructions I reduced it down to about 5-6 dist degrees using a rubber bushing to reduce the arm travel on the vac adv can.
Seems to have done the trick as I do not hear pinging under high gear lite acceleration.

 

Thats not quite correct. The wrench is used to define when the advance comes in, it doesn't adjust the amount of advance.
As others have posted, to adjust the amount of advance you either need a bushing, an adjustable cam or weld up the slot. Probably other ways.

Talking of using a bush to limit the advance, any one got any pictures showing what they used/did?

 

That's not quite correct. The wrench will adjust both amount and rate on the Accel advance 31034. I have one installed and it does exactly as advertised. Great for fine tuning the advance.
http://shop.accel-ignition.com/adjus...points-v8.html
With the Accel advance you can still use a bushing, etc to fine tune.

 

Some adjustable vacuum advance cans come with a cam that lets you adjust the amount of advance, like so:

http://www.summitracing.com/parts/cr...FU4F7AodV0wAPg

Scott

 

I stand corrected guys, my bad for giving wrong info!
Are all adjustable vac cans the same then? Im sure the one I had said it just changes when the advance comes in but as I didnt want to use it I may not have read the instructions......real guys dont read instructions, right? lol.

 

My policy is to throw the directions in the trash.....that way, when I finally give up and decide to read them, I know where they are!

Scott