Thread: Sudden problem, truck dies at idle and some black smoke from the exhaust

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I agree with Roger. My first thought was what is the fuel pressure (if a carb?) , what's the float settings? Just replaced the fuel filter? If not, how old is it?

Black smoke is a to rich mixture, 1 or 2 fouled plugs don't usually cause black smoke.

Well heres where I lack expertise. It is carbed but I havent put a gauge on the rail. I know the pump is working good, I've just done the fuel filter. This is what gets me. I've been driving the truck for almost a month now in all ranges of temps and it starts right up with no hesitation. So why now something is different I'm not sure.

All the plugs looked pretty bad, I have no idea how long they had been in there but I'm guessing awhile. Then I found that the distributor cap has a gash inside it now as well, it's not cracked though. How I have no idea.

Secondly this is a 750 carb, granted the motor is .30 over with a mild cam I'm wondering if this is to much? Maybe it's fouling the plugs with to much fuel and I'm just looking at it to hard.

I've never dealt much with having to adjust or troubleshoot carbs so this is a new one to me.

Seems to me that your carb is over-sized. I would think that a nominal 600cfm would be more suited to your 350 +0.030 engine. Sure, you can jet the 750 down, but as you jet it down you're looking at reduced air velocity in your venturi, which is going to affect efficiency. Is this a new-to-you truck, or one that you built or have had for a long period?

This is a new to me truck and I didnt get a thing on documentation. So its all figure it out.

Again, I agree with Roger. A 750 wouldn't have been my first choice... many folks make a 750 work on their SBC's so there's no reason you can't - unless you've never done this kind of work before! In that case I'd suggest you find someone local or prepare yourself for a learning curve.

With some patience and a reference manual, I'm sure you can set the tune-up where it works as desired. Fix the ignition system first, you can't sort out a carb with a suspect ignition!

Yea I have my ignition parts being delivered from summit tomorrow. I'm pretty incline and can learn. I would love to learn about dialing carbs in. I tuned in my 600 holley on my mustang a few years back but not much more than that. As for mechanical experience I designed and installedmy own turbo kit for my daily driver back in 04.

I started off doing body work on an 86 celebrity in high school, Ive swapped engines, rear ends, transmissions.... The usual. But I grew up around the street rod shows in York pa. My dad took me every year, I can still remember dreaming of owning one. However mechanical skill doesn't run in my family, so everything I've done I taught myself by failing or learning through forums like here. It's been a long road but so much fun, I don't regret a bit life's to short.

Ok well upon dealing with the plug and wire issue the thing is still running horribly. So I started with inspecting the carb, I found one leak where the fuel line connected to the carb and fixed it. I then noticed a leak on the other side of the carb behind the electric choke, it looks to be a plunger of some sort for the secondaries. After pulling the air cleaner I noticed a good amount of fuel from that leak down in the intake manifold.

So is it worth being rebuilt or would you go with a smaller carb like others have recomended? If so what any help there is appreciated.

Originally Posted by 1923tbucket

So is it worth being rebuilt or would you go with a smaller carb like others have recomended? If so what any help there is appreciated.

Since the truck is new to you, if it's been running OK then I would probably assume that the previous owner tuned the carb right until I saw evidence to prove that wrong. You may find that the PO went through the whole process of re-jetting the carb and making it right. I'd probably invest in the rebuild, then see where I stood relative to plug color, response, mileage, etc. An easier way might be to just buy a new 600, but I tend to be a bit frugal.

The second leak is the one that would get my attention. You say there is fuel down in the intake manifold? This is inside the carb? Raw fuel? To get a better understanding of what is going on you will need to start the engine with the air cleaner off. While it is idling look down into the carburetor, you should not be able to see any fuel going into the engine. If you see fuel then you can see the problem, ok? If there is fuel coming from the top of the vent tubes then the needle and seat are stuck and not able to shut off the fuel; if you see fuel coming out of any of the 4 boosters (they are those legs sticking out into the venturiis) then the idle is too high or the fuel level is too high. After a good looksee shut the truck off and look again into the 4 boosters, if fuel is dribbling out of any of the boosters then the fuel in that section of the carb is too high and you will ahve to lower the float.
Again, if the engine is at idle (800rpmish) you should not be able to see any fuel going into the engine, the engine at that point will be supplying fuel thru the idle circuit only.
If you raise the rpm to 1200ish you should see fuel coming from the bottom of the boosters, the fuel should be kinda atomized and the droplets should be uniform in size and consistancy and they should be trying to form a bit of a 'cone' under the booster.
If your idle is 1200ish, then you need to lower it down. If you can't lower it then we need to do some advanced troubleshooting looking for other things like vacuum leaks ok? When you solve all the problems it will sit there and idle at 800ish rpm no problem.

Use a face shield to protect your eyes and face from a motor backfire.

No I should have written a little clearer, the leak is on the outside of the carb sitting down in one of the crevisis on the outside of the manifold. I'll go get a picture here and post where it is coming from. I just can't see how it suddenly started one day and caused an issue

Here is where I caught the fuel drip. It's right behind the choke

That is likely fuel running from the throttle shaft. It shouldn't do that on the scondary but it can do that on the primary.
Did you look inside the carb while the engine is running or with the fuel pump running? What causes fuel on the throttle shaft is when you shut the engine off a few dribbles come from the booster and land on the throttle blades which are closed because the engine is turned off - we are talking in a millisecond type time frame here.
The fuel dosn't just run into the engine as much as it runs down the throttle shaft and exits the carb at one side or another.
The problem i see is taht the fuel is on the secondary and since it is sitting in the garage and if the engine has been run it has just been run on the primaries so there should be no fuel any where near the secondaries. That is why you are going to have to look down in it when either the motor is running or the fuel pump is turned on. It sounds to me like the rear float is too high and needs adjusting down, we just have to prove that that is in fact the case.
I hate those carbs, i have a pair of them right now on a tunnel ram that i am trying to get sorted out - just hateful things the 4160.

I didnt I got a bit irritated with it. I will say that normally one pump of the gas and the thing would fire easy every time and there after when it was warmed up you would never have to pump it. Now you can barely get it to start and keeping it running is about the same.

It's just weird that it randomly started one day while driving. It had given me some crap one day driving around town and it straightened out and never occurred again until the other day. It's cranking easy and just not wanting to fire, almost like my mustang when the vacuum advance was bad on the distributor when it had points, this of course does not. With that we could get it to fire and drive and then it would act up, there are just a lot of things to look at.

I know how frustrating it can be.
Your problem, the sudden onset of it etc, sounds worse than i first thought and i am know thinking that it is a piece of trash gotten to the needle and seat. The needle and seat is under the nut/screw on top of the bowl - nut/screw are the adjusting means for the needle and seat. The needle and its' seat is the valve taht allows fuel to enter the bowl, when satisfied a float mechanism closes the needle and seat to shut off the fuel - exactly like the float on your toilet bowl and when they don't work right they can't shut off the water/fuel.
In a carb when that happen fuel will exit the top of the carb via the vent tube - they are at the leading edge of the venturii, the tubes that stick straight up. When needle and seat get trash in them fuel will flow out of the vent tube and mostly run into the engine flooding it and getting as you descibed black smoke.
With engine or fuel pump running you will be able to see it happen. It is very dramatic.
Don't feel discouraged, i am still working on the carbs i was grumbling about yesterday, i now have the plugs out for a look. These things are a challange, that is part of our attachment to them. If they didn't challange us we'd soon get bored and take up bass fishing.