rochester 2g will not idle below 750-800

71 cj5 with a 225 with th350 and 2g carb. I rebuilt the carb with all new part(power piston,power valve,brass float and .51 jets). I have set the timing with timing light(10), set dwell with a dwell meter(28) and adjusted the ldle mixture screws with a vacuum gauge(20-22). All that being said i cant get the thing to idle below 750. You can take the screw out and still no change. Also i had to turn the idle mixture screws out 4 turns to make it run. It has a very rough idle at 750 and idles better at 1000 rpms. I'm stumped!! Too big of jets or something else. Runs good at speed. Any advice would help!

 

Sounds like a vacuum leak......


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That's what it acts like but i sprayed carb cleaner all over the motor and nothing..

 

Might also try removing the idle mixture screws and bLowing out the passages with compressed air. I had a similar issue and it doesn't take much debris to clog or restrict the passages in a 2g.


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excessive wear in the throttle shaft?

 

Could be your engine/carb combination is just happier at 1000rpms.

 

I tore mine down, all the way. When I put it back together I had a few things close, but not quite right...

A good soak in solvent and a bath in the ultra sonic cleaner with white vinegar and a bit of tide detergent got it clean.

The accel pump hanger needed to be flipped over as I had a WOT condition, had to readjust the float...

Other than that, I put .050 jets, rather than use the .051 which were there. All new parts that I could find... Quadrajet.com kit and all extras...

I polished all the other pieces to get them rust and oxide free and that seemed to let me get the idle down as low as I can and still keep it running.

 

I blow out the idle mix screw holes and double checked the float and pump. All looks good. I still have a dead spot off idle and will not idle smooth below 850. I still am wondering if the jets are too big. How do you know if your jets are to big and what size should they be. Im about to lose my mind!!!

 

Are the mix screws still turned out 4 complete turns?
Should only be 1 1/2 to 2 turns max.

 

Check the spark plugs. That will tell if running rich.


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Yes 4 whole turns. It will not idle at 2 turns. I will check the plugs this afternoon.

 

What distributor? You are set at 10 degrees btdc, but the book says for either 5 or 0 for the stock distributors.

 

Stock dizzy. I set the timing at 10 cause of the auto transmission. It's real rough idle 0-5

 

Stock dizzy. The points window is between the 1 and 2 tower on the cap I set the timing at 10 cause of the auto transmission. It's real rough idle 0-5

 

What screw are you taking completely out? (first post)
And you state you have a TH350 behind the V6. Does that make this a 2wd vehicle? The CJ5 isn't a long enough chassis to have an auto with a t/c behind the engine.
The timing for an engine with an automatic tranny is different than for one with a manual tranny. By 2º to 4º .

 

Member Daryl regularly puts TH-400's in 3B's and early '5's without modifying the wheelbase.

Back to op. might also check for vacuum leak at the line going to the transmission modulator valve. You would need to plug off the line going to the trans and see if there is a difference.
Gotta ask, did it do this before the carb rebuild? Why was the carb rebuilt?


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I'm 100% sure it can be done (th350 in a cj5) cause I did it.

It all started when I went out of town and when I came home the jeep had a dead battery. A friend of mine tried to drive it, when I was gone but said it wouldn't start. I put a new battery in it and it would start if you hold the pedal down but not idle like it had a huge vacuum leak. Changed the points but nothing. I finally got it to run and idle rough after changing the elec. fuel pump to a original manual pump. And I have been trying to get it to idle right every since.

 

what was the fuel pressure of the electric pump, what is the pressure now.
and how is your charging system? how did it drain down so bad, key on dead coil, dead resistor?
my gut is telling me you need wot to start to lessen the load on the starter enough for it to fire the ignition and the lighter electrical load from the mechanical pump just helps it fire the coil, try a 12v wire to the ignition + from the battery with it running.

 

That could be the whole problem. Fried coil.
And like Nickmil says, check that modulator connections at both ends. My '78 Cherokee did the same thing, and what I found is that someplace that I was off the road with it a branch or something caught that line under the vehicle and pulled it off. Instant vacuum leak!