Advanced Timing

[bliebler]

The timing at idle on my 73S calls for 5 deg ATDC. I'm not sure if this is set for pollution or to help start up as the piston is going down at that point. I have advanced it slightly, 3deg ATDC, and the car responds better off idle. Even at 2deg ATDC which is advanced 3 deg the car performs much better and I don't have any hard start issues. The full advance appears to come on a little before 6000RPM however, I never did trust my Sears timing light. I had to close my air bypass screws a little to adjust to the higher idle due to the advance. This makes the idle a little richer. Prior to this I had timing set to the Factory spec 5degATDC and played with my idle making it rich by 2 clicks, however, I still had a litttle hesitation off idle. Has anyone else noticed this, any thoughts?

[orange911]

Check that you do not have any carbon blocking the vacuum ports that feed the vacuum pod on the distributor. Also, make sure that your dizzy is advancing per the advance curve for your car. Check it at idle, 2000 rpm, 4000, and 6000 rpm. I know that mine was not advancing right and I discovered lots of wear in an original 90k mile dizzy.

My advice is to eliminate an extra variable. Do this by setting the timing at idle with the vacuum retard removed. If you do not see at least 8 degrees advance when disconnected, then you have a vacuum problem. The vacuum, if strong enough, is suppose to retard the timing about 10 degrees. Now, if you have a vacuum leak or a bad vacuum pod, this will not happen.

Example: Lets say you are leaking vacuum at a TB and you do not know this. Per the tune up instructions, you are suppose to set the timing at 5 degrees retard, right? OK, you adjust the timing with the vacuum hose connected to 5 degrees atdc. Now if you pull the vacuum hose off, it should read 5 degrees btdc. But in reality with a significant leak, the timing might be at TDC or even less. This was how I knew that I had to have a vacuum leak. Also, the higher idle will produce less vacuum and also reduce the amount the pod retards.

Now, lets say you over compensated the advance on the idle timing so that it was at 5 degrees BTDC. You will now be too advanced on the rest of the curve. Now throw in the worn mechanical springs in the dizzy, and you are advancing way too fast. Dizzys are not rocket science, you just need to have a reputable shop rebuild it, if a rebuild is in order. I think this is just good maintenance every 60k miles. I send mine to Advance Distributors and have been very satisfied with his work and price. I know there are people that will charge you $300-400 for a simple rebuild, but again, its not a specialty like MFI pumps.

[bliebler]

Thanks for your advice on my timimg issue. After checking everything out I have come to the conclusion that my problem is not a timing issue. When I rebuilt this engine I installed a light weight flywheel and I believe that is giving me a little erratic idle and that hesitation off idle. If I set my idle at 1000/1050 RPM the idle is smooth and off idle improved. All this is well worth it because the car revs much better than before.