Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
lean and variable A/F ratio
blarson:
Ahh, it sounds like I didn't attach the clip correctly. I unknowingly ran it though one of the holes instead of over the back of the float. Full throttle is in the range of 13.5:1 so perhaps the clip position is making the float a little artificially high. Crazy thing is that I drove the truck about 150 miles today and the amount of time spent super rich seems to be getting shorter and shorter. I really can't explain that. The carb hadn't been run for years and was pretty corroded. I did soak it in carb cleaner and blow it out with compressed air. My original hypothesis was some corrosion that I didn't succeed in getting out but now that you point out the correct clip position....... Time to pull the airhorn again.
I'm not sure if this is related but I am also getting some backfire through the exhaust that is progressively worse the faster I lift the throttle. I perceive that to be related to a leak between the manifold and exhaust pipe due to a stud failure that I'm taking care of on Monday. When that happens AFR goes lean while it pops and then rich once the engine slows to the point where backfire stops. We'll see what happens when the stud is fixed. The O2 sensor is on the other side and there isn't a crossover in the system so it's a little perplexing. I was assuming that exhaust was contaminating the intake. We'll see.
As a side note I've been turning in the APT a little at a time to set cruise now that I've had more time to drive it. I'm back down to 4 turns now with freeway cruise fluctuating between 14-15:1
blarson:
I lowered the float level to 3/8 and the extreme rich idle condition following full throttle decel appears to be gone now. My AFR fluctuates quite a bit at constant throttle settings but watching a bunch of youtube videos and seeing essentially the same thing leads me to believe that to be normal. Normal like a worn out ignition system I cannot say. I'm going to leave well enough alone with that particular issue until I can get it on a dyno.
My last two problems are this exhaust backfire on full throttle lift decel and some choke issues. I'm going to fix the exhaust leak before blaming anything on the carb. I think all I need to do with the choke is replace the metal coil. It doesn't seem to want to close all the way anymore but also doesn't want to open fast enough to avoid a very rich condition about a minute after start either.
Thanks again for the help everybody!
429bbf:
couple of things the round brass thing that you backed out with a screwdriver in one of your earlier posts is the top limit adjusment for the power valve.when mash it to the floor and loose vacumn your spring maybe pushing the needles up to high out of the jets.i had to play with my carb a little bit to get it set right. one last thing is your vacumn pulloff working correctly on the choke?or when you step on it is the choke flopping in the breeze causing crazy readings.imo
blarson:
Thanks! I did screw that limit screw back in a few turns it leaned the truck out a little at WOT. I kept it around 14.1 but it sounds like a little richer than that is actually a touch safer and won't materially impact my fuel economy or emissions. I resolved the exhaust leak today and that actually smoothed things out considerably to the point where I'm not bouncing around a full point on the AFR anymore. I essentially disabled the choke until I had funds to buy a new one by turning the cap all the way open 100% of the time. I'll be sure to double check the pulloff at the same time as soon as I replace it just to confirm that last little bit of bounce isn't related. Thanks again everybody!
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