Ok I have a 390 with a standard 2barrel carb and I just replaced my intake manifold gaskets and put it all back together but then my carb started making a poping noise like it was going to backfire everytime I hit the gas.
Finally last night I started backing out the adjustment screw on the right and the popping stopped, or at least it slowed down noticibly and now only does it so often when I'm driving down the road. But the problem is it seems to be idling pretty fast and when I try to adjust the idle screw to slow it down it wants to stall or idles like crap. On top of that the engine almost sounds like it's ticking which I think is because it's running so rich?? When I started backing out the adjustment screw on the right I mean I had to back it WAY out, like 5 1/2 or 6 turns. This can't be right can it? Should I look to change jets and if so what would be a good option?
This is my first time messing with my carb and the only reason I messed with it was because I've got noone else to help me out.
Also I dont know if this has anything to do with it but I noticed all the vaccume lines join into one big line and go over to a black round thing on the driver side wheel well. The big line was unplugged from it but I think it is supposed to be plugged up there. When I did plug it up it actually seemed to run worse! Should I just leave it unplugged then? Could this be the cause of my problems? When I had it unplugged and plugged it still made wanted to backfire untill I backed out the mixture screw out like that.

 

Hi JWest,

The sputtering\backfiring problem on acceleration is not related to the idle mixture screws. These only control the air\fuel mixture at idle. The accelerator pump is in charge of richening the mixture when you hit the gas. If you have to keep the mixture screws out more than 2 turns, you most likely have a vacuum leak. With the sputtering, high idle, inability to have a low idle, and the fact that you have the mixture screws out at 6 turns, you definitely have a vacuum leak. I noticed you said you changed your intake gaskets - I bet that's your culprit. Or, there is a leak under the carb base. One way or another, something didn't seal up.

The black round thing on the wheel well is a vacuum reservoir. If you have a vacuum line that is hanging off the engine, this is a vacuum leak too. You can't have any vacuum leaks at all.

Other possible causes of your sputtering\backfiring issue include improper timing and faulty accelerator pump. Regardless, adjusting the idle mixture screws isn't going to get you anywhere with respect to this problem.

 

so if you can only adjust the mixture at idle then how the heck would you adjust the mixture for all other throttle positions? you can have a perfect idle mixture but it runs richer than bill gates any other time? i am just wondering how you can pay so much money for a carburetor and all it does is make your truck run worse than stock. i happen to have an edelbrock and it runs rich.

 

It has to be tuned for the engine with metering rods and such. Every engine requires a different mixture. No universal carb is going to run perfect out of the box.

 

Well I got it running good. The big vaccume line that goes to the vaccume resivior caused a huge vaccume leak and made my truck run like crap. I thought it didnt make a difference but it does! lol I got that plugged back in and it's running pretty good again it still has an occasional pop every once in a while but I've got to change the oil like, asap. I guess from all my tinkering I had the gas so rich that it actually got in the oil. So I'm changing my oil tonight and hopefully it'll be back to 100% again.

 

FYI - If you have gas in the oil, your fuel pump is going bad. You cannot get gas in the oil by having the carb set incorrectly, no matter how rich you have it. The two don't have anything to do with one another.

Gas in the oil is bad. If you just change the oil without correcting the problem then you're going to get gas pumped into the fresh oil. Gas in the oil is caused by the fuel pump getting ready to go. Are you positive that you have gas in the oil in the first place? One way to tell is to smell it. Another way to tell is if the oil level becomes mysteriously high all of a sudden, since the last time you checked it. The fuel pump on my 351W gave out a couple years back, and after I replaced it, I noticed that the oil was about 1/2 quart higher and smelled like fuel. I changed it right away.

 

Well...... damn.
I think my truck hates me.

 

Make sure you actually have gas in the oil before you take anything on. I can't tell you whether you have gas in your oil or not; I can only tell you how to find out and what is wrong if you do.

 

Yeah I already smelled it. It's gas. That was the first thing I did, the lifters started ticking and I shut it off immediately then pulled the dipstick and smelled gas.