383 intermittent misfire

[johnnycharger]

Hi All
Ok so today I checked the fuel level through the site plug. It was good. I hooked up a vacuum gauge and tried to adjust the air fuel mix. I started at the default of 1.5 turns out like stated in the Holley video. When I adjusted the screws I really didn't see much change. How far do you need to turn it before it affects the vacuum?
I looked down the carb while it was running. I noticed the "butterflys" were completely closed. It is also very loud. Sounds like it is struggling to suck in air. The butterflies looked like they had condensation on them. I don`t know if it was gas or not. It is running smooth except for if I stomp on it. It has a momentary hesitation then it goes. I drove it for 2 miles, looked in the carb again- now the butterflies are dry. Pulled a plug and it was dry and black. I don`t know why they are black again.

[johnnycharger]

Quick thoughts - bc the people you have responding already will give good advice and know more than me.

If you mostly idle, the plugs can get dirty pretty quick and foul.  I have been able to clean and run them without replacing. I am sure you know that already.

I believe your ignition is OK.  I had mine cut out intermittently because of a poor connection at the firewall, and I often have suspected at the battery.  I have also had a coil warm up and do this.  My guess is that these are not your problems.

Re the carb and timing:  Have you adjusted the idle mixture with a vacuum gauge (vac advance unplugged) after the car is warmed up?  This might be part of the dirty plugs.  Also, have you adjusted the timing (vac advance unplugged) after the car is warmed up.  I found with my car that advancing the timing to where it idled most smoothly and the idle speed stopped advancing with timing (the issue with running higher initial is the full advance curve - which you don't want being too high) and then after that, I reset the idle speed screw and then readjust the idle mixture using the vacuum gauge.  For my car, this helped keep plugs cleaner because it ended up being a leaner setting.  They then stopped fouling and the idling did not lead to an eventual misfire from fouled plugs.  My inclination would be to see if any of this helped and then work from there.  Stumble and other issues will be outside the idle circuit on the carb. Those can be dealt with once you are satisfied with the idle.

If someone posts and says this is not the first thing to check or there is something else.  I would go with that over what I have suggested.

   

Thank you for the good suggestions.

[johnnycharger]

https://youtu.be/dPmuvoWyA7Q


Here is what the carb sounds like. I can hear it louder than the exhaust. Is this normal?

[nvrbdn]

If you can totally cap off the air draw through the carb and not stumble the engine, I would say you have a bad vacuum leak somewhere that is drawing major air. Either a rotted hose, or the gasket under the carb. Check for any vacuum ports on the carb that are open, or a leak in a vacuum hose, power brake booster, anything drawing vacuum from the manifold.

[c00nhunterjoe]

   but that will go terribly lean, and your plugs are wet and fuel fouled in minutes. Massive vaccum leak and over rich.

[johnnycharger]

So tonight I looked for a vacuum leak and had no luck. I looked over the carb and vacuum lines and found no signs of a leak. I also sprayed carb cleaner on the lines and gasket surfaces as well as the manifold fittings and had no luck.

[krops cars]

When you put your hand over the carb it should have died or idled  lower. I did not here any real difference. I agree nvrbdn try a vacuum gauge. You should have 18 to 22 inches of vacuum. Let us know what you have. Do you have another carb to try? Also. How old is the fuel? You maybe trying to chase something that might not be the issue.