In the pictures below, the tube in question is seen to be connected to nothing at either end. It seems to me that it has something to do with intake. What is it and how important is it? It also seems that the engine could go for a healthy cleaning. The contrast between the spark plug wires and the valve cover has me suspicious, and it looks like it might have either a valve cover gasket or head gasket leak. Exhaust manifold and O2 sensor look to have seen better days.
That tube pulls warm air from the manifold to assist with warming the carb up when you first start the truck. You need to re-connect it or cap it off at the air filter or else you'll suck water into the engine the first time you drive through a puddle or in the rain.
Ironraven is correct the heat tube is disconnected at both ends and the open tube where it is supposed to attach on the airbox could suck in water.....looks like you have some kind of either corrosion or red clay coating most of the engine block??...pressure wash and degrease the whole underside to get rid of it and then lube the hell out of all the moving linkages (especially the carb)..that coating all over the engine can trap heat and cook the motor...
looking at the pics again ..I think you may (or previous owner did) have a cooling system issue...check to see if you have actual coolant in the radiator..my bet is there is only water in it...looks like rusty water has been spraying the engine for a while ....
Has anyone ever found a good product to replace the tube? Mine is brittle with duct tape holding it together
Engine Yes, this thing needs to be cleaned in a bad way. I pulled the engine cover and snapped some pics. I've never seen anything quite so crusty. The previous owner did at least have enough sense to plug the intake hole. The plate at the exhaust manifold is going to have to be replaced. I don't see enough left to be able to connect to, but why are there two holes? Next, possibly a stupid question. Where do I check the radiator fluid?
...you seem to have a truck that saw a lot of clay dust...wow it's baked on...like in a kiln...HHmm..just me ,but I would nickname the truck "Oast" pronounced ..OH-ST ..Welsh I think..for kiln used to dry barley for making beer..... seriously though I would get that grunge off asap....clay is a superior insulator and won't allow heat to radiate off the engine..the rad is under your seat .heres a parts breakdown of the exhaust and intake...the flex piping can be found at any good auto parts store..or pirate one from an auto wrecker..
Get yourself some "engine degreaser", spray cans; buy a box, 24, I think. Soak and spray, soak and spray; HI-pressure washer. I'm going to say from a mine operation. If you're not going to use the truck at outside temperatures below -20degC; I'd say dump the carb heat exchanger system completely. It really is overated anyway. The thermostate controler for this system is in the air box and controls via vacuum to the air flow exchanger. The pipe you are missing goes to the underside of the truck bed, passenger side; just like the other side of the bed. My system has been completly garbagetized and everything works just fine. Remove the vacuum "T-off" (connect strait to) from the back of the air filter box and go with a strait flex pipe from the air filter box to the truck bed. Eliminate all mechanical parts in between including air flow exchanger (black plastic box with 3 air connectors). You really don't need it.
Engine No pictures yet, but the engine has been cleaned. I started by rinsing it to try to wash off some of the dirt, then sprayed it with degreaser and let it sit for a while. I bought a brush with nylon bristles to help remove the stubborn stuff, and it now is much improved. The first couple times I started the engine afterward, it had a stuttering problem, which felt like not all cylinders were firing. Something was obviously still wet, preventing it from working like it should. When I started it the next day, all was acting normally.
Something else I have recently been made aware of is that I believe eventually you'll suffer from Carburetor Icing if you don't have that warm air intake... I'm not sure if that's 100% true or not but something to think about.
Cleaner I got a chance to snap a few more pictures this morning. While I still wouldn't want to eat off of it, the engine is cleaner than it was.