Carb heater?

[mrtleavitt]

Ok, I'm still fighting a small miss on cylinder #4 on my 390. Everything appears to check out ok, plugs, wires, cap, rotor, timing, compression, and everything else I can think of. I was talking to my Grandpa who is the man when it comes to old fords. He is the one I bought the truck from, he's had several mid-60s thunderbirds with Fe engines, so he knows what he's talking about. He was telling me that the only other thing that he had heard about this problem is if the engine doesn't get hot enough then it might have problems burning all the gas, which makes sense because cylinder #4 is farthest away from the main water passage. He then explained that's why the stock setup on the Fe motors had a heater line running through the base plate of the carb. Plus, I'm running a 160 degree thermostat compared to the original temp of 195. So, he convinced me that this could be my problem, has anyone else heard or experienced something like this? I've always wondered why Ford ran a heater line through the original carb but never dug into the physics behind it, but obviously it has something to do with the Air/Fuel mixture. Any comments?

[BRUTUS_T_HOG]

gasoline (or any liquid fuel) doesn't burn unless it's vaporized.. so that coolant line through the base of the carb is to help the fuel turn into a vapor so it can burn in the engine.

the thermostat could definetely have an impact, but also you could have arcing from the spark plug wire or the spark plug could be too cold to keep contaminates off

[fomocoguy]

I wouldn't be too concerned that you don't have the coolant heated spacer anymore, because when the engine is up to operating temperature the bottom of the intake gets hot enough to vaporize the fuel, that is IF THE ENGINE IS GETTING UP TO NORMAL OPERATING TEMPERATURE. In my opinion 165 degrees is not normal operating temperature. You will probably make more power and get better mileage (due to more efficient fuel atomization and complete combustion) with the original heat range stat. That being said, if the miss is present from the moment you start the truck it may not do a thing. My advice: spend $5 changing the stat and see what happens. I've had a number of cars run like crap when the stat stuck open and the car couldn't get up to normal operating temps.

[mrtleavitt]

Ya, I totally agree about the thermostat, but it bugs my that there was once a carb heater on there, obviously for a reason. I just figured if the designers of the engine knew that it was needed, then wouldn't it be wise to keep it on the motor? Maybe the normal operating temp wasn't enough to vaporize the gas? I don't know, just thinking out loud.

[71PA_Highboy]

The reason for the heater was not to help atomize the fuel, but to keep the carb at a constant temp over different ambient air temps.

Once the engine is at temp, the water running thru the carb heater is actually cooler than the bottom of the intake (180 vs the exhaust temps in the crossover and the oil temps).

The other benefit is that in the wrong conditions (or right depending on your point of view) it can keep the carb at operating temps and prevent the carb from icing over (and yes, I have had this happen to me).

hth,

eric

[mrtleavitt]

Good info, thanks everyone!