make sure that the vacuum advance hose is attached to the fitting at the center body of the carb. this will give you ported vacuum and cause the advance to only be there when the rpm's are above idle, if it is hooked up to manifold vacuum, it will have advance all of the time and it will affect your performance. the way to tell is when it is idleing, take the hose off at the distributor and put your finger on the end of it, if you can feel it sucking, it's hooked up wrong.
when you set the timing, disconect and plug the vacuum hose at the distributor, that way you set it with only initial advance. and like I suggested before, set the timing at 10 degrees, it will run better still and shouldn't cause it to ping.

so you know, the 71 1200 did not have EGR, if you are refering to that pipe at the left rear of the block that is about an inch round and a hose going to the intake manifold, it is the PCV system.
the PCV system and a primitive vapor recovery system are all the emission controlls that they used on 71 to 73 USA models.

I found the timing mark and it is set at 5 BDC as the manual states for N. America. The carb is a new rebuild manual choke variety. The dwell angle reads 52 degrees. I have no standard air cleaner. The only hose that plugged into the old one was the vent line from the gas tank and it doesn't draw a suction or anything. The PCV works OK, just got through checking it. I was screwing around with the old suction lines (only the EGR and distributor have them) and they need replacement so that should help. It ran better after pushing them on tighter. I replaced the coil and in the process switched the wrong wires to the - and + tension leads. Got those back and it has acceleration again .
There have been no engine tear downs except replacement of head gaskets throughout its life. It is tight and leaks no oil or burns any oil. A very clean exhaust. I just got through with a test drive and it seems strong, just not quite smooth on idle. I'll try to include a photo on the avatar when I get around to getting one.
I certainly appreciate all the help. This old thing will be up and running good again soon I'm sure. Many thanks to all and I'll keep you apprised of the situation.

Good point rgrinder ... dwell can cause rough running, as does bad points. I worked on a Chevy with that problem last year. It would only run at high idle, and not very smooth at that.

I would like to add it's likely you can solve this without spending money replacing any parts. Too often guys start replacing parts (cap, rotor, plugs, etc etc) without fixing the problem. Even with used parts it should still run smooth. The points are the most likely to go bad, and a dwell meter will help tell the story there.

Another thing to check is the play on your throttle shaft. These carbs are old now and they wear immensely. I had to put on a Holly/Weber just because I can't find a stock carb that doesn't have a worn out shaft. A worn shaft makes the engine idle rough, and/or kills the engine at stops and it can not be tuned to idle correctly.

Mareo

it almost sounds as if you need to go back to the basics.
first pull and check the gap on the plugs, spec is 0.030-0.035, it's best if you set them at 0.030 as they will wear to a larger gap. then set the points (this is assuming that you are running a point type distributor) use a dwell meter if at all possable, it is much more accurate, dwell spec is 49 to 55 degrees, again try to get it set to the lower figure. after you have set the points then set the timing, I always ran mine at 15 degrees (second mark) because of altitude, you might be best off setting yours at 10 dergrees (center mark) only set the timing after the points are set, the reason for this is that for every 1 degree of change in dwell, the timing will change 2 degrees and this will affect the way that it runs.
good luck

Quote:
The A12 engine is very smooth and quiet. This high idling is usually caused by a vaccuum leak (unless your carburetor is shot).

Examine carefully all the vacuum hoses on the engine, especially the ends of each hose. Plug temporarily the hose going into the PCV valve (in the manifold, just under the carb) to see if the engine slows way down. Also plug temporarily (as a test) the hoses: vacuum advance on the distributor, the small hose going to the air cleaner, and the hoses going to the circular diaphragms on the carburetor. Just put a golf-tee or something to tightly plug the end of the hose.

If nothing shows up, spray the carb-manifold junction and the intake manifold-head junction with WD40 -- if is smooths out while spraying a particular spot, tighten the bolts or replace the gasket. The idea here is that the oil temporarily plugs the leak and you can hear the engine run differently.

The TDC timing mark is almost certainly the biggest mark of the five (the last to line up in direction of rotation). If there is a bigger mark in the middle, that's the stock timing mark. Newer engines had the timing marks on the front cover (clearly marked with numbers), with a single mark on the crankshaft pulley.

If your camshaft is off a tooth, that might cause very rough running ... have you changed the cam or had the engine apart?

Thanks for the reply. My idle doesn't smooth out until it is around 1000 rpm. I can never get it down to 800 without the engine jerking around and running rough. Even my 4 cyl Nissan truck runs like a sewing machine but the 1200 is really rough. I'm still trying to confirm the TDC mark on the pulley, but the ignition timing looks correct with the light and all best I can tell. I just changed out the coil now also. I can get the thing to start and run, but again low idle and slow driving under a slight load and the engine runs bad. I'll keep working with it.

there are actually 2 different screws, 1 to set the mixture with, and the other to set the idle speed with. you found the mixture screw, the speed screw is the one on the side to the rear as I remember with a spring arround it too. some call this one a throttle stop screw. adjust this one to raise your idle speed, and then adjust your mixture screw for the best idle smothness. once you have raised the speed, you should be able to turn the mixture screw in more and get things where you want them.
remember that as the speed screw is turned in (clockwise) the idle speed will increase, if you have a tach. set it at about 750 to 800 rpm, THEN adjust the mixture screw.

30 weight synthetic is good, I use 10W-30 regular oil myself. 20W-50 was not the recommended oil originally.

30 weight is used where it doesn't get too cold (stays above 40F). 10W-30 has a [url=http://www.castrolusa.com/expert/ae_article.asp?article_id=16

Thanks for the reply and yes, it's an A12 engine. While going through the manual one more time I noticed that I don't use the recommended weight oil. I guess I better upgrade at the next change. I been running a synthetic 30 wt. instead of the 20w-50 that the book says. Hmmm, hope that didn't affect the operation of this old thing too much. I noticed "dimlight" on the board. Great, he doesn't live too far from here & thought I might have lost him at the first of the summer when the computer crashed.