engine goes extremely lean off idle

[matt69olds]

My Edlebrock 1910 850 Q-Jet is giving me fits! Idles ok, just off idle it goes dead lean. Higher throttle seems to get better but still lean. Retorqued intake manifold, inspected all vacuum hoses, sprayed carb cleaner all around the manifold, no change. I have a LM-1 in the car, Idles around 14.5-15.1, and jumps around. Driving the car, just off idle goes 18-19, with the trans in park it goes off the scale (22.1) it started doing this all of a sudden, before tearing into this I would like some ideas on what to look for. At this point I'm reasonably confident it's a internal problem. Any ideas or suggestions?

[omaha]

 I will assume this is a 69 olds [lol] . While wideband O2 meters are great tools, I feel they are not the correct tool in certain instances. My opinion is they are not good for setting the idle. The idle circuit greatly affect the off-idle. I would try setting the idle with a vacuum gauge. A lean mixture does not always mean a efficient mixture. The vacuum gauge is a much better indicator for idle situations. Sometime it ends up at 14.7 afr but most of the time it doesnt.  If you richen up the idle it will affect the off idle too. this may not totally solve the problem but I bet it will make a difference. If you still have lean off idle, then you can deal with idle circuts and enrichment circuits and accel pump etc.. But first I would start with setting the idle with the vac gauge and then making sure the ignition advance is steady and working correctly. the widebands are great but a carb is not easy to tune for straight line readings through the "ranges" [RPM, load etc.] {also remember the E-fuels have a different AFR number so you have to run them richer {depending}. FWIW.

[matt69olds]

The timing is locked at 34 degrees. I do set the idle with a vacuum guage, with the big roller cam the idle vacuum is somewhat smooth at around 13 degrees. I don't rely on the wideband for calibration, it is nice to have to confirm suspicions. In this case, the engine runs very rough off idle, as does at cruising speed. I can crowd the throttle and smooth out the engine, as soon as I let off the throttle it starts to surge and run rough again. Itjust started doing this last week. The accelerator pump has a good steady stream of fuel with throttle movement. Any other ideas?

[omaha]

now that I think of the problem a little more with more info that you have given, I am leaning toward some type of debris that might have got lodged into the idle circuit. The "all of a sudden" aspect is what is leaning me in this direction.  Do you have a vacuum advance distributor on your Olds. Sometimes, vacuum advance cans will go bad and make idle and off idle driving a problem. Last on the list could be fuel pressure problems and maybe but not likely, needle and seat and/or float issues.  But, most likely it is something to do with the idle / transition circuit. It is just not getting the fuel for some reason it seems. And, it may be possible that it's only doing this on one side of the circuit {eg. clogged needle opening on the passenger side}.  I would think that the idle for that cam would be in the 13 - 13.5 range on the AFR readings. Good luck my friend. Keep us posted.

[matt69olds]

I did an "autopsy" today, the carb was clean on the inside, I didn't find any debris. I have blown all the passages out, made sure the are all clear using a small piece of wire. I decided to swap in a .149 needle/seat (it had a .110) without the window, I hope this helps with the excessive cranking after sitting. The only issue I did find was one of the outer tube in the top plate that feed the holes above the secondary air door had fallen out. I replaced it, and tapped it in place with a brass punch. The needle and seat pass a vacuum test (as outlined in cliffs book) with or without the vacuum advance functional makes no difference, I'm running a RobbMc 1100 mechanical fuel pump with a holley regulator set at 5.5, the fuel pressure gauge is electric I can see it when I'm driving. I'm putting the carb back together tomorrow and reinstalling it. I have a friend with the exact same carb, if the problem is still there I'm trying his carb. If it still does it with his carb, looks like I need to dig into the engine. Thanks

[Cliff Ruggles]

Edelbrock 1910's came with many different calibrations in them.  Most were actually set up rich at idle and off idle, not lean. 

Nothing was mentioned about the jets, metering rods, power piston spring or if the hanger arms were level and exactly even, which more times than not is the issue with these things.....Cliff

[matt69olds]

I purchased jets and idle tube from you a couple years ago, made a huge improvement in the way it ran. I don't recall what the specs were. Like I said, this happened all of a sudden, went from running like a champ to running like crap. The 

[Cliff Ruggles]

I'd pull it apart for a complete cleaning, and replace the main players, float, N/S assembly, and accl pump.  That should get it back up and working like it's supposed to.....Cliff