1977 LM-1 bone-stock 350, smogger equiped; Starts fine, idles fine and has no problem from take off to cruising speed. Only problem exists when I mash the peddle to the floor. Car just bogs down for a couple of seconds and then finally takes off. Can you give me a list of possible problems that are causing this ? Thanks !

 

Problem sounds like typical "quadrabog" symptoms. Here's the usual culpirts:

1. Secondary accel tubes have gotten clogged or fallen off inside the carb. It's rare these days but it still happens. No way to know without taking the carb airhorn off. There are 2 brass tubes on the airhorn that suck raw fuel from 2 oddly-shaped fuel reservoirs inside the carb's min body. If those tubes are clogged or have fallen off you will get a serious bog off the line. Also, there is a very tiny fuel restriction that lets gas into these fuel wells. If those restrictions are clogged up you will get identical symptoms.

2. Seondary rods are often very lean and will cause a pretty bad bog on a modified motor. If you could tell us what secondary rods and hanger is in your carb now that would be helpful. THis is often 80% of the reason these carbs have a bad rep.

3. Secondary air door tension spring is too tight or the door's movement is sticky/gummed up for some reason. Air valve tesnion spring should be at 3/4 turn from the zero tension point for starters. if you're not sure how to adjust this, just post back- someone will help you out.

4. Secondary vacuum break canister (vacuum can on the pass sicde, front of the carb) is releasing too slowly. Stock it should take about 1 second to go from fully retracted to fully extended. If yours takes significanly longer you'll want to replace it. Also, make sure it's adjusted correctly. The little metal pushrod that goes back to the secondary air door arm should have just a TINY bit of slack in it with the canister fully retracted (enough to let the air door open maybe 1-2 degrees). Adjustement is done by bending (yes, BENDING) the metal link back near the air valve arm until sufficient slack is achieved.

5. This is a rare one but there is plastic cam that lifts the secondary rod arm higher as the air valve opens. If it's worn down it won't lift the secondary rods out of the jets far eough or quickly enough. At max lift look where the arm contacts this cam. if there's a little "notch" there it indicates that the cam is worn down slightly. It should be a smooth curve all the way up and beyond where the arm contacts even at max rod lift/air valve opening.

 

Thanks for the reply Damon,
I have no idea what secondary rods and hanger is in the carb now. As far as I know and very certain that it's the complete stock cc q -jet from a 1987 LG4 T/A. Though the LG4 is no longer in the car, it was swapped for an older LM-1 350. It appears that all of the smog equipment, CC components, and ECM are all original to the 87 LG4 and was put on the 350. I was wondering if the ECM for the 305 is affecting how the 350 runs at this point. Other than the bog when I mash the pedal to the floor, the motor runs perfect. I also noticed that the EGR valve appears to be caved-in alittle on the top, but i can still feel tension from underneath the valve and am able to push it up and the motor will stumble but not die. Don't know if this has anything to do with the problem of the bogging at WOT but thats about all that I can find wrong with the motor. What is your opinion on this Damon ???? Thanks !!

 

Definitely check the tension on the air valve. This improved the stomp it to the floor reaction of the car immensely.

If the carb was on a 305 and it's on a 350 now, your secondaries may be to lean. I'd pull the rods and find out what you've got. Easy enough to do, just be sure you put them back the same way you found them, and be careful with that little screw.

The ECM controls the idle/part throttle mixture on the primary side. It also controls the distributor timing.

The problem you're having sounds a lot like the problem I was having. I also had to adjust the idle air bleed some.

You can find a good description of what to check and how to adjust here... https://www.thirdgen.org/newdesign/tech/quadrajet.shtml

 

If it's really the original carb from an LG-4 it should have a set of really lean CH secondary rods. A switch to a set of DR rods, used on the L-69 HO 305 (that used an otherwise identical carb) will make quite a difference, assuming everything else is in good working order.