My 75 is running a M4MC quadrajet over a 350. A couple nights ago "flames" were coming out and tonight it backfired. The problem is intermediate and when it the problem is present the slightest push will get power but past that the pedal just feels boggy unless you floor it, risking flames and backfire. The idle screws are turned about 2- 2.5 turns out. The bigger idle screw on driver side is pushing a little to raise idle(). I have heard things about the APT(?) or maybe this is the accelerator pump. Also I am not totally carburetor terminology savvy.

 

I hope one of our talented/expert tech member's can help you with your problem.
When was your last tune ? Plugs/wires/ignition etc ?

How many miles on your 350 ?
Has the carb been rebuilt ?
It helps if you can put as much information as possible into your post to help member's ~>Help you...

It's sometimes difficult to help with just words and not being there to hear/test drive, so post as much information about your problem that you can....Good Luck

 

Thank you for the friend invite & response, God Bless you. Roughly 40,000 miles maybe less. Wires replaced within a few weeks and I checked the new ones for damage earlier tonight. Timing set at ~6 degrees. I did not replace spark plugs but I got the car in August. Carb was rebuilt(paperwork says and overhaul) maybe in 2001.

When I first got the car, (no custom exhaust or any work on carb by me) it had a slight delay from stop to accelerating and would sometimes stall from stop.
At first the choke was suspect. I cleaned it(just spray choke cleaner) and observed it to find the it was functioning(based on my observations) and didn't appear to be a problem. Then I discovered the idle mixture screws. Probably tuned more those times then I needed but I felt I was learning.
Then I learned of the other idle screw on the driver side which actually lowers and raises the idle rpm(to best of my observations).
Now through all this the slight delay never left entirely and the car would often still stall from say backing up.
I felt the engine bogging the night the flames spat and all I thought I had modified was the idle screws.

This sounds like the accelerator pump? I read this can be a gradually worsening problem and sounds suspect to my problem.

If you need more details, HOLLAR

 

Once more, inconsistently the engine will run proper it makes me jealous.

 

Below is from a Google's Search...I hope it may help until one of our expert member's can make a suggestion/solution to your problem. Check out the below links:


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1

 

Hey. Back firing thru the carb sounds like a timing issue! Check that & your spark plugs. Also if you have a vacum leak. It will run like crap. Also check to see if your spark plugs wires are on tight. Also their might be a leak around the carb base.

 

The backfiring I was aware of was from the exhaust pipe(Sorry I didn't state that earlier). Umm I am pretty confident its not the timing, I have checked it twice and the problem intermediately comes and goes. I can't imagine a vacum leak causing this large of a problem that comes and goes either. If I'm wrong correct me and thank you.

 

Sorry if I shut you down but you may be right Rick I always noticed fuel around the carb and ignored it.

 

i will check if it is getting the proper spark from the coil and i will double check the gasket for the carb as well because it might need a thicker one. what i mean is the gasket wich the carb sits on. also check the bowles on the sides of the carb to see if it is getting to much air or might be leaking. also see if it is the fuel pump or fuel system feeding the system to much one time to little the next. after running the basics like you did leaves few check points.