Until the early 1960s, these blow-by gases were removed simply by letting air circulate freely through the crankcase, wafting away the gases and venting them as emissions. It's also undesirable because the unburned gasoline in it can gunk up the system and produce problems in the crankcase. This escaping gas is called blow-by and it's unavoidable. However - and this is where crankcase ventilation comes in - a certain amount of that mixture of air and gasoline is pulled down by the piston and slips through the piston rings into the crankcase, which is the protective cover that insulates the crankshaft. Meanwhile, the rising piston pushes the air and gas left over from the explosion back out of the cylinder through an exhaust valve. The rotation of the crankshaft not only pushes the piston back up into the cylinder so it can do all this again, but it also turns the gears within the car's transmission that eventually make the car move. The pressure from this explosion drives the piston in the cylinder downward, where it causes the crankshaft to rotate. A mixture of air and gasoline is pumped through a system of tubes called the intake manifold through each cylinder's intake valve (or valves), where a spark from a spark plug causes the mixture to explode in the open space at the top of the cylinder called the combustion chamber. Okay - one, two, three, go!Īn internal combustion engine is built around a series of hollow cylinders, in each of which is a moveable piston designed to glide up and down inside it. But to do that, we're going to have to give you a quick refresher course in how the internal combustion engines found in most automobiles work. Or at least it shouldn't seem complicated after we've finished explaining it to you. But it really isn't all that complicated. Unless you're a real gear head, just seeing the phrase "positive crankcase ventilation" probably makes your head hurt, because it sounds, well, complicated. The two "towers", for lack of a better term, located in front of the choke plate, should be bowl vents.Alexey Dudoladov/the Agency Collection/ Getty Images You would have to remove the airhorn to check for sure but, there should be three open vent holes into the bowl. If everything works, it runs good and you're satisfied with it, you shouldn't have to change anything.Īs for the carb bowl vent, the plugged hose was likely the vapor return line to the vapor canister on whatever vehicle the carb came from. If it were my engine, I would probably connect it that way but, that's just me. The PCV, transmission and power brakes, if your truck had them, would all get constant vacuum from the manifold. The PCV valve goes into a thick hose, then into a reducer for a smaller hose, then plugs into the carb on the front drivers side, under the accelerator pump. Right now the threaded hole on the back of the manifold is connected to the transmission, so if I connect the PCV to it, where would I connect the transmission hose? Or would I add a splitter? The hole is in an intake runner so would be a vacuum source. On this manifold, you could use the large threaded hole at the back for the PCV hose fitting. The port on the back of the manifold connects to the transmission on mine, I assume that's correct. Mac3687 wrote:If it helps in the meantime, here's the spacer I have: I have no idea if the current setup is okay or if I should change anything. Gasket #1933 adapter in place, which does not have that big PCV port on it, hence the routing you can see in my drawing. Because the previous owner put a 2 barrel carb on a 4 barrel intake, there's a Mr. The big thing that I'm confused about is every photo/diagram I see shows a carb spacer that has a vacuum port on the back, that links directly to the PCV valve. I can take photos, but I figured this would get the gist of the routing across: I am however a tinkerer and I've always worried I didn't have everything connected right, and am ready to fix it. I've had the truck for three years, it's been my daily driver for most of that time, and it generally seems to run fine. My dilemma is that I have no idea if my vacuum lines are routed properly. No dashpot, but there is a choke unloader (or are those the same thing?) Forgive my ignorance here, I'm more of a motorcycle guy, and when it comes to some items on my truck, I'm a little lost.įor reference, here's what I'm working with:ġ969 F100 (I was told the engine was from a 1970 truck)
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