I'm still having fits with my timing...........(taking it to a shop in the morning however).

Been trying to run between 16-18 intial, with 18* bushing, which should, and does put me at about 36 total. Problem is, she runs hot (was pushing over 220*) there when cruising about 70 on the highway. I can slow down to 60, and she will back down to around 210*.

Came back to the garage, backed the timing down to 14*, and ran the highway again. This time, she never got over 200*.

To much vac advance? At 14 initial no vac, when I add vac I'm at 30* at idle........

 

i have been using 10 degrees from the vacuum advance for several years, when i go over that (to 16 degrees) we tend to have pinging and overheating problems that go away when the advance is reduced to 10 degrees(using 36 total mechanical advance all in by aprox 3200 rpm).

i have read many posts that disagree with a 10 degree limit to the vacuum advance but it works for the engines i work on and the reformulated fuel in california.

 

Your timing issues are more complex than you may think. A properly "timed" engine only performs at it's highest when all other factors are considered. Take fuel ignition for example. First, rich mixtures ignite easier and burn quicker than lean mixtures. Rich mixtures occur at wide-open throttle (WOT) and under heavy loads (such as pulling a trailer or driving up hills). Second, dense mixtures in the cylinder (which occur at or near WOT) burn quicker than sparse mixtures (also called “weak” mixtures that occur under part throttle conditions). Combining these fundamentals results in the realization that “rich, dense” mixtures burn very quickly and do not require as much ignition advance as “lean, sparse” mixtures. The engine requires much more spark advance (from the distributor) during part throttle operation than during a full throttle drag run or when it is required to pull a heavy load on hills. To get the proper ignition timing, your vette uses a “mechanical advance” system (consisting of weights operating against springs) to compensate for engine speed; and a “vacuum advance” system (consisting of a vacuum diaphragm that moves the breaker plate) to compensate for engine load. At WOT there is no engine vacuum and the vacuum advance does not work. Combined, the mechanical advance and vacuum advance allows the engine to run cooler because the extra advance at part throttle will fire the lean mixture earlier so that it burns at the piston dwell point at TDC. Without the vacuum advance, the timing is retarded, and the piston is on its way down the hole exposing the cylinder walls to the heat of combustion and overheating the engine. I would suspect that your vacuum advance is suspect. Also, be sure you allow these mechanisms to achieve the total advance you are looking for and not to set your initial advance too high.
Good luck!

 

It was my timing light............dayum........

I thought I had reduced timing to 14*, but when I took it to the shop they checked, and it was 23*.......freaked me out!! Suprised I didn't blow the biatch up as well!! I you wonder why it wanted to run hot....

Tossing the cheap timing light away.......righ now!!

 

Dayum. Ever run it without Vac. Adv.?

Brett

 

That is one area that some of us forget about. The calibration of our equipment. It seems that your light was off around 9-10degrees. That would be pretty serious misadjustment. At least you only overheated and not blew something up.

Now is your chance to get an adjustable timing light.

kdf

 

No, but have thought about it. Not really sure I need it, not a DD or anything.....

 

If you're going to run your 36* total from the distributor only, then unhook the vacuum advance and leave it off. If you're going to run 36* total from the distributor and vacuum, then you'll need to back off of your mechanical adv. a few degrees to limit your total adv. to 36*.

Got a timing light yet?

 

I remember you saying that u didnt have the correct balancer installed. Did you ever get the correct one installed yet?

 

Balancer checked out fine. It is the correct one for my motor.

**Just got the timing light delivered. Went with a digital Innova with advance and tach.

 

Where did you get it?
Cost?
Why that one?

Thanks
Wade

 

Not really true. You have to set up your mechanical advance to give a maximum advance of 32-36 degrees. The exact number is dependant upon your combo and what your engine likes. Full advance should come in by 2500 to 3000 rpm again dependant on what your engine likes. There should be no mechanical advance below 1000 rpm. Once you have that you can add a vacuum advance canister to add an additional 10 degrees. This will give you a total of 42 - 46 degrees. But that will only happen sometimes. If you are driving below 2500 rpm you do not yet have full mechanical so the vacuum helps it along. If you are running WOT you don't have vacuum anyway so you get what the mechanical dial in is. The reason stock distributors like a lot of vacuum advance is because they have very slow mechanical advance curves. My 74 was still advancing at 3500 rpm and probably did get full mechanical advance until 4K or over. When you quicken the mechanical advance to come in sooner you have to limit the vacuum advance to compensate. If I'm wrong someone will correct me but this is my understanding. Lars?????

 

Hooked up the new timing light........got 10* when "dude" said he set it at 16*...?? WTF? Reckon he was on the #3 plug wire? One of us doesn't know what he's doing......With the new light I click the advance button until the TDC mark lines up with O on balancer tab. Then check the reading....15*. Can also just strobe and see where the TDC mark is on the tab...right at 15*. Correct? To check my advance, I set the light on 36*, and rev'd upwards towards 3000 rpm while watching the mark. It gets to just before the 0 mark on the timing tab.

Put her back at 16*, then backed down to 15*. Was tipping out over 36* around 3000 rpm. The new light is nice! Has a dual screen showing digital timing and rpm.

How much vac advance should you get at idle?

 

Got in from Summitt.......was a little over 100 bucks.

 

From your description that sounds right. I have one of those timing lights also. They work really well! Are you using the 21* blue bushing? The MSD vacuum can is a 16* unit. Depending on the amount of your vacuum at idle the can should be pulled all the way in....thus adding 16*. Add that to your inital and that total should be what your light shows at idle, assuming your using manifold vacuum. I think I said that right.