okay guys i havent posted in a while, but i yet again need the help of you guys. i have a 79 bronco with the 351m/400 v8 in it i was having minor idle problems before i did my upgrades, but not as bad as now. i put a edelbrock streetmaster 400 manifold on her and a 650cfm holley double pumper carb. now im getting a loud pop from under the hood evry now and again it sounds like a backfire through the carb but being in the truck driving its kinda hard to get out and check. second problem is when i come to a stop at a light or something i have to keep my foot on the gas a lil to keep her from stalling while in gear.if i put her in neautral its fine. i set the idle speed up to almost 900rpms where as before i could sit at a light and idle at 200rpms and be fine but now when she tries to idle even with it set so high she still tries to keel over and die. im thinkin it maybie a vacuum problem from the booster, but i dont know.

any suggestions?

 

The two problems are probably related, and to the carb - since they started after you put the carb on. There very well could be a vacuum leak, the first place to look is the carb's base gasket (you did put a base gasket on, right?). Re-torque the carb. I would also re-torque the manifold to specs. Then check your air/fuel mixture screws. Have you checked them? Two full turns out is a good rule of thumb to start with.

How did you jet the carburetor? Do you know if it is jetted properly for whatever your elevation is? The "pop" noise could indicate a lean condition.

As far as that manifold and carb, are they matched for your motor? If you have a stock motor, your carb and manifold may be too much for it. Double pumpers are not necessary on stock motors and are harder to tune; they were made more for racing than for everyday driving.

"i set the idle speed up to almost 900rpms where as before i could sit at a light and idle at 200rpms and be fine but now when she tries to idle even with it set so high she still tries to keel over and die."

It used to idle at 200 rpm's? That's not really even possible. When you say that it is close to 900 now - a stock truck in park will idle pretty close to 900. When in "D" my 351 idles 700-750, and a little higher in "P". I've never seen anything that could sustain an idle at 200 rpm.

Also check your timing, I always re-check the timing after making engine mods. Your symptoms do mimic those of improper timing, although it could be one of a lot of things. Start with the carb though, since your problems started after you put it on.

And a long shot - is that manifold new? Maybe it has a crack in it?

 

did you adjust the float level for your carb after installing it? i definately agree with j about the lean condition. this could be caused by a vacumn leak or by low float levels.
if i remember correctly there are two plugs on the side of the carb one for the front float and one for the back float. if you remove these you can raise the float level by turning a screw on top of the carb slowly until fuel just trickeles out of these holes. then you reinstall the plugs. once you have done this you can put a vacumn gauge on the engine and see if you have a leak. remember that if the timing is off you will get a low vacumn reading so you better adjust the timing first.