intial advance

[Keith1365]

i finally got ignition control up and running using direct coil on a small block chevy. The motor has been running fuel only for several years. I am planning on a power adder as a winter project so ignition timing will be important. I have tried several spark advance maps and have started tuning. I have one map that runs fairly well but the idle afr is about 12.1 to get it to idle. it then accelerates well but has a slight hesitation then runs great. I have been experimenting and to get a good idle with an afr in the 13 range without surging, it is asking for about 31 degrees advance at 800 rpm. This is 9.1 compression aluminum head gen 1 small block with a long duration camshaft. Just wondering if it is normal to require that much advance at idle or if I am missing something.

[kjones6039]

That sounds like a lot of advance to me! I run a similar engine and run 16-18 degrees at idle.

Can we assume that the timing has been confirmed with a non-adjustable light?

Ken

[Keith1365]

After checking, this is about the same timing it had before I converted to ignition control. I have 14 degrees initial and about 12 degrees from the vacuum advance so it had a total of about 26 degrees before conversion. Maybe I am out to lunch but it idles better with more advance. Before, the air conditioner compressor kicking in would make it stall unless I turned the idle up to about 1,000 rpm. It will now idle at 850 and the air can kick in and out and only lose about 50 rpm. It has not melted down yet and does not ping off idle. It still has a little bog from a very slow roll but the afr is going off the scale lean for a split second also. I guess I will try to reduce the timing right off idle to see if it is over advanced in the 1200 to 2000 rpm range and then try some more accel fuel.

[kjones6039]

..............then try some more accel fuel.

That will likely take care of that 'bog'.

Ken

[kjones6039]

After checking, this is about the same timing it had before I converted to ignition control. I have 14 degrees initial and about 12 degrees from the vacuum advance so it had a total of about 26 degrees before conversion. Maybe I am out to lunch but it idles better with more advance. Before, the air conditioner compressor kicking in would make it stall unless I turned the idle up to about 1,000 rpm. It will now idle at 850 and the air can kick in and out and only lose about 50 rpm. It has not melted down yet and does not ping off idle. It still has a little bog from a very slow roll but the afr is going off the scale lean for a split second also. I guess I will try to reduce the timing right off idle to see if it is over advanced in the 1200 to 2000 rpm range and then try some more accel fuel.

Just re-read your post.......... You have locked the distributor I suppose?

Ken

[Keith1365]

distributor is locked. Played a little more tonight. Was able to take idle timing down to 27 degrees and still maintain an idle with the air on and get it to idle with an afr of around 13.2. Reduced the timing advance at low rpm up to about 2,500. if you stab the throttle, the afr goes lean to about 17:1, spikes and then goes to about 10:1. I am assuming not enough accel fuel initially but then not enough. Not sure how to correct. I can only go up and down the road a couple of times a night without wearing out my welcome with neighbors.