81 in stock condition with egr valve removed. Carb rebuilt because it was leaking and running bad at idle. New plugs. I set the timing per manual. Timing at 6 degrees with est disconnected. 26 degrees with est connected at idle and will jump to 36 at idle. 48 degrees all in at 2200 but you can see the timing is not smooth. Now I get erratic idle and it fails emissions at idle but passes at 2500 rpm. Any ideas whats causing the high advance at idle to be so high. Thanks Dave

 

I hope you used someone who knows Quadrajets when you have it rebuilt....seeing how you still have the same issue at idle.

The carb could could be leaking excessive fuel at idle. Do the idle mixture screws work??? Do you know how to check them to make sure they are working CORRECTLY ???? Because if they are not...you have no way of correctly setting the idle mixture and it will give you problems...period. Especially at idle. BEFORE cranking the engine...turn the idle mixture screws in until they seat. DO NOT TIGHTEN THE TO DEATH!!!! Count the number of turns for each idle mixture screw. Then back them back out to where they were. This will give you your "baseline setting". CRANK the engine ...get ti to idle and turn ONE of them in and see if the engine dies...or has a really hard time running. Then back it back out to where you checked its setting initially. Then do the other idle mixture screw the same way. IF the engine dies...then the idle mixture screws are able to be adjusted....IF when they are turned in all the way...and the engine is still running...your carb is leaking fuel and you can not meter the idle circuit...thus making you have a rough idle

You CAN NOT trust the mark on your balancer ( unless it is a new balancer) for timing. I have encountered numerous balancers over the years that the outer ring has spun and will give you a headache trying to use the notch as a perfect reference. You have to use a piston stop device in number 1 cylinder and manually spin the engine until it hits the stop- and mark the balancer and then turn the engine the opposite direction and ,mark it when it stops to verify that the notch is correct. Between your two marks on the balancer will be TDC.

Is your centrifugal advance is working in the distributor correctly and not hanging/binding up.

I have also noticed that sometimes the vacuum advance that I get in from a parts store is NOT correct. it will bolt in place ...but the cut-out for the advance is NOT the same and often times will allow the timing to be allowed to advance more...due to the limiting of the rod is increased due to the cut out is longer. I have seen it many times.

This is where I would start and or check. The obvious vacuum leak check. And remove and PLUG off the vacuum hose to your headlights and HVAC from the fitting on the intake. I have seen the headlights causing a vacuum leak and makes the car run like crap when it is connected...and when it is removed and the fitting capped off...the engine runs much, much better. I had one the other day that was just like that. the headlight actuator relays were leaking VERY BADLY.

DUB

 

throttle position sensor and/or map sensor.

have you put a meter on to check the carb dwell?

 

This is an 81 ecm controlled. Tps is new and set at .056v at idle and moves with throttle advance. And dwell is at 30 degrees for the mcs when the idle is steady. Is the idle timing suppose to be at 26 to 36 degrees at idle. Dave

 

nope
6 deg plugged or not

 

Another common problem is the O rings on the idle air bleed valve fail...which cause the idle to do strange things.

Spray a little silicon around the base of the idle air bleed screw and then count the turns as you remove the screw. Check the O rings, replace if needed, spray a dab of silicon on the O rings and re-install the idle air bleed screw to where it was.

The idle air mixture screws at the base: turn all the way in with the engine running and engine should die. If not, then there is a leak, either air or fuel....although strange that dwell is showing 30 which is correct.

Let us know what you find-out.

 

Timing set at 6 with est unplugged. est plugged in I have 26 degrees with a jump to 36 degrees all at idle. I will check the mixture screws tomorrow. One thing I noticed is when cold with timing light connected at start the timing was at 6degrees as engine warmed up timing went to 26 degrees later jumping to 36 degrees at idle. How much does the temp switch control timing. Dave

 

Been awhile since I set stock timing, but with computer disconnected I remember 6 - 8...and it should not change with the computer disconnected.

Now when the computer is connected, the timing will change when it goes into closed loop. I remember seeing a value in the 20's range right after connecting, so the #'s you have seem similar.

But I would also check the balancer....it may be shifting on ya. Yes bit of a PITA to check but sounds like it is necessary.

 

timing is not controlled by idle screws or bleed off.
30 deg says it is fine.
timing is done by
rpm
manifold vvac
baro pressure
throttle pos
HEI module.

carry on