as most of you know i made a 302 with a 600cfm carb stack ignition(duraspark), .060,280 cam,speedpro coated hypereutectic pistons anyway, i have some autolite platinum plugs that i bought.took one out the other day and the tip was a greyish white, like it is running lean. but it can't be when i rev it up it blows a little black smoke out of the pipes. i also have a high volume electric fuel pump. what is the cause of this. i tried to adjust the mixture screws but i am not good with that stuff,maybe i need my friends dad(he is a mech.)to look at it. it has a new 1406 edelbrock carb.

 

adjusting your mixture screws is not gona do anything for your lean condition, all your mixture screws does, is controll your idle circut, once you crack the throtle they have nothing else to do with carb. a puff of black smoke could come from the initial shot of gas from the acelerator pump. i've not had any dealings with edlebrock carbs but sounds like you need some more fuel. DW

 

i have a 1406 and it runs really lean also. They were tuned for maxium economy accordingly to edelbrock.

 

speaking of maximum economy, i havent seen a SBF yet that didnt like to run slighty on therich side. DW

 

i have a 390 bbf.

 

I belive the person who started this thread and whos question i responded to said they had a 302 and last time i checked it was a SMALL BLOCK. DW

 

you have a 600cfm carb on a 390. that is your problem don't you think

 

i thought black smoke meant it was rich. i had a cheap electric fuel pump on it before and when i stomp it to the floor it would cut out somewhat. but that pump went out already and i traded my friend for a higher flow pump it does not cut out anymore. i am wanting to get a msd 6a ignition so maybe it will burn all the fuel in the cylinders, correct?

 

as opposed to the stock 356cfm 2bbl!

 

The reason the plugs are white doesn't have as much to do with the fuel mixture as you'd think. The reason your plugs are white is because they are too hot. You need to buy plugs 1 or 2 heat ranges cooler. Cooler plugs have a longer insulator core which protects the electrode from excess heat. Since you have your engine built up, I assume you also increased the static compression. Any time you upgrade the compression, ignition, or use power adders (nitrous, superchargers) you need to use a colder than stock plug to prevent preignition. You probably don't have preignition now, but the plugs are obviously getting hot enough to turn white, so they won't last as long as they're supposed to. I don't know much about Autolite spark plug numbers, but for instance, an NGK UR-4 is the stock replacement spark plug for a '77 302, a UR-5 is one heat range colder, and a UR-6 is 2 heat ranges colder. Try swapping for colder plugs, and then see how that does. You can also rig up an O2 sensor into the exhaust if you really want to know how you're running. The Edelbrock #1406 comes from the factory with #94 jets, which is indeed the best choice for fuel economy, but I've found that in modified to highly modified engines, I get identical fuel efficiency but greater performance with #98 jets. The stock metering rods may be too large (secondaries too lean), but this is extremely vehicle-dependant. The fact that you can actually tune your secondary fuel mixture without modifying the metering block is why Edelbrock carburetors are superior to the modular (Holley) design. Let's get plugs that are a bit cooler first so that you can gain insight to your fuel mixture by looking at your plugs. TK

 

A little black smoke out the exhaust can also mean leaky valve seals. Do you like to hot rod your truck a lot? Your high volume pump what kind of psi does it run at. I know edelbrock recommends no more than 6psi which my stock fuel pump puts out a couple psi more than that and it runs fine, if the pump is putting out a great deal more then you could have problems from that, but I don't really think that applies here. A grayish white plug I think that is fairly normal unless you are experienceing pinging or some other running problem. Good luck

 

If its valve seals it would be a oil leak (white or grey) smoke, Black smoke would be gas, Not valve seals. DW

 

DW2455
Your right I got my wires crossed when I wrote that, it was late, I did not intend to misinform.


F100guy
The black smoke could also be due to your ignition being off, so you may want to have your timing checked, just to cover all the little things first it could very well be your problem. Is the carb new or did you get it used. If its used and you have the time get the number off a metering rod and jet and myself or someone can tell you what you have and where you stand from the stock setting, great thing about these carb you can remove and replace metering rods or step up springs literally in minutes and the jets in a coupld more, gotta like that. Later

 

everything on the motor is new along with new rebuilt heads. the pump is about 7-9 psi.