Need Carb help

[LannyL81]

My 81 passed emissions, but just barely at idle....213/220 on HC.....running rich....this is the E4ME carb. I had trouble getting the idle air bleed screw dwell adjusted. Manual says it is very touchy.....mine is the opposite. I can turn and turn it and sometimes it changes dwell, sometimes it does not. About the only thing that causes a change is to fully seat it. I must have an air leak somewhere as I seated the idle mixture screws and the engine barely noticed it, it should have stumbled and died. I have tightened all the carb body screws...and the carb manifold bolts....still no change, checked all the intake manifolds bolts...all tight. Any hints as to where to look next?? I had rebuilt the carb a two years ago, but it has just been sitting on a shelf until I got the engine running now for the past three months.

Thanks,
LannyL81

 

[bigvette1]

Idle Air Bleed

Usually you have about 1 turn on the idle air bleed. I would first set the idle mixtures screws out 3 turns. Then hook up a tach/dwell meter on the green pigtail off the mixture control solenoid - this is a test point. On the 6cyl range the dwell should be running about 30-35 degrees when totally warm and in a closed loop mode. If you are constantly at 50 degrees or way less than 30 you are in open loop and running way rich. Also, put a vacuum gauge on the manifold vacuum port and see how much you are pulling. Should be between 17-19" unless you have a long duration cam.

The idle air bleed is one of the adjustments but remember to get into a closed loop you need a good O2 sensor, the mixture solenoid tapping away (is it?), and the idle mixture set near the right range - if not the ECM is controlling the mixture. Also, the temp sensor on the intake is a feedback to the ECM that will make the thing run rich until warm. The manual should have the flow charts on the carb controls.

If you don't have them, send me an email and I will scan the charts and email them to you. JP Use:
bigvette1@hotmail.com

 

[LannyL81]

I have the idle mixture screws at 3 1/3 turns out according to the 81 Service Manual. I let it run for a good five minutes to get into closed loop; have the dwell meter connected to the green test connector and reading off of the 6 cyl scale. The mixture control solenoid is clicking away. Dwell reading is between 35 and 45, changes almost each time I try....unable to get it to go down to 30. It is a new O2 sensor, mixture solenoid travel at 4/32", about 700rpm idle.

Now what?

Thanks,
LannyL81

 

[bigvette1]

What?

You sound like you have done everything to set up the carb correctly and it is ok. The only thing is a slightly high dwell reading which may be ok also as long as it varies with speed increase and returns to a fairly stable setting and less than 50. What is the vacuum reading at idle? If it is stable between 17-20" you don't have a leak in the mass of Vette hoses.

Maybe the carb is just too rich from too high a float level if the HC on the emission test is too high. If you passed then leave it. If you think you need a new carb or to get yours rebuilt, two places that I have had good succes with is Recarbo and National Carbs. Both have been fair with good results.

 

[Mr. Chuck]

Check the vac hose and fitting real close; just had to replace / trim several split hoses at their respect fitting and replace two tees that had cracked with time and heat, especially if you milage is getting up there. My 81 has 126K+, so I make a point to first check all hose on a regular base or if she starts to act up.