Firm

My bone stock non-CCC (Canadian Spec) LG4 has always (as long as I've owned it at least) had a tendency to idle a bit rough, only when it's warm, when it does do, it also smells a bit rich.

Over the years I've done all the usual stuff (ignition tune up, vacuum leak check/repairs, etc) so I've pretty much got it narrowed down to the idle mixture settings.

I spent some time over the winter reading up on how to adjust these, and bought one of the flexible adjuster tools with the "double D" end. It's still a bit too cold out to do the job, but I poked around under the hood and tried to get my adjuster tool onto the mixture screws. Fortunately the 'plugs' have already been broken out of the factory Rochester Qjet, and I can just barely see the little adjustment screw heads. I cannot however get my adjuster tool even close to fitting. The 'Double D' screw heads are sitting so close to the casing that I don't think my socket will fit around them. Even if it did, there's so much crap (mostly vacuum lines) in the way that I can't really get even the flexible tool in there.

Knowing that I would need to adjust these with precision to get the settings synced up the task seems nearly impossible. Now, if I had the carb off the car it's be simple to do, but obviously to adjust these right the carb needs to be installed, correctly hooked up, and the car running.

Any tricks I am missing?

sofakingdom

iTrader: (1)

First off, if they were adjusted properly at one time, they probably still are... they don't generally move around on their own. Only reason they're "off' usually, besides the motor underneath them getting changed, is human interference. Meaning, if they haven't already been tampered, they're probably just fine. Which having the anti-tamper plugs broken out is not a good sign; but if it ran OK at one time but has got worse, they're not the issue.

Kinda like "timing"... if I had a dime for every time I had seen some g00b got a wild hair about how his "timing" is "off" without giving the first thought to how such a thing could even happen, I'd be a VERY wealthy moron by now. And my cash register would cha-ching MANY more times a day. I think I might just copyright that phrase, so I can collect royalties. Hmmmmm....

Single most likely cause of your troubles, is leaking plugs. A number of the passages in that carb are drilled from underneath; and when that was all done, the factory spun in some aluminum plugs to restore the bottom of the bowl to fuel-tightness. Problem is, the plugs are aluminum, but the carb body is chinesium; and the 2 VASTLY different metals in intimate contact, form a little battery, which creates dissimilar-metal electrolysis. The chinesium erodes and turns to a white powder. And once that happens, the metal is GONE FOREVER, leaving a ... hole.

Virtually EVERY ONE of these carbs develops this problem sooner or later. Kinda like, there are only 2 kinds of hard drives; those that have crashed, and those that will crash someday. These carbs are EXACTLY like that.

So, put a more or less infinite supply of gasoline on one side of a hole, and vacuum on the other, and the results are pretty predictable. The carb leaks fuel into the intake. The leak is worst at idle, when vacuum is high. The mixture goes stoooopid insane rich, but unevenly; and the car stinks at idle, gets HORRIBLE gas mileage, fouls plugs, and runs bad.

The cure is, take the carb off; take the throttle plate off (the 2 rearmost air horn screws, and 3 screws in the bottom, then finagle the accelerator pump linkage a bit); wire-brush the plugs; sterilize them with some NON-RESIDUE solvent such as lacquer thinner, acetone, or MEK, but NOT brake cleaner, paint thinner, or mineral spirits; and epoxy them over real good. Wait for the epoxy to set up overnight. Then put the carb back together and install it WITHOUT TOUCHING ANY ADJUSTMENTS WHATSOEVER, and enjoy.



The ones numbered 1 & 2 aren't the issue; they CANNOT leak into the intake because they are surrounded by a gasket. Leave them alone. 3, 4, & 5, 6 are the culprits. 3 & 4 leak into the intake, 5 & 6 just drip on top of it. Chances are you'll see the evidence of that as well.

Firm

Wow, great post. I'd never heard of that, but it seems plausible. Guess I'll need to pull the carb and have a look, definitely a warmer weather job, but I appreciate the advice.

DoctorStoopid

Sorry to resurrect a year-old thread, but I thought this information was really helpful and maybe someone else could benefit from seeing this detailed writeup.

I've got a question myself related to this: I'm currently in the process of "rebuilding" a quadrajet but I'm only at the "taking everything apart and soaking it in carb cleaner" stage. It's the original 80,000 mile CCC carb and it's never been rebuilt. All of the rivets and idle mixture plugs are still in place. I've had to drill out the thermostat cover and IAB cap, but I REALLY don't want to bust out the mixture screw plugs unless I have to. Here's the question:

This carb was running fine when I pulled it off the car. It had a bit of a shaky idle, but nothing terrible and it would cruise with no problems at all I chalked this up to it needing the plugs epoxy'd and gaskets refreshed. If it was pretty much running acceptably before, is it a safe bet I can just dip it, rinse it, reassemble it, and not worry about touching the mixture screws, or should I just go ahead and do it anyway since I'm already this deep into it?