73 Chevy C-10 Pickup straining to keep running

My father passed down his 1973 Chevy C-10 pickup truck to me and my family. It’s been our ‘runner’ truck for many years going to the mountains for wood, lumber from the store, garbage and yard debris…etc. Unfortunately, it recently has been starting and warming up just fine, but once it’s running as I’m driving away from stops or even holding speed on the highway the power ‘fades’ from the engine and it lugs like it is in gear, but flooded and lurches as the engine seems to ‘catch up’. I have replaced the carb(holly quadrajet), fuel pump, fuel filters, battery, fuel lines, throttle cable, distributor cap (ceramic piece too), alternator and more…we still can’t get it figured out. NOW the truck won’t start or turn over - have we reached the end of it’s life no matter what we do? What is left to replace? I don’t think we can afford much more $ to fix it. We also found that somehow water was in the gas tank, which we think was from a kid in the neighborhood messing around. Could that have made a permanent issue?

The best way to figure something like this out is to have one’s hands on the truck, but I will try to help you. A compression test will tell you if the engine is worn out, so that is a good place to start if you suspect that. A vacuum test is also a good idea to diagnose this since worn cam lobes are rather common on small block Chevys, although this doesn’t sound like the case. Beyond that, I would start with the ignition system since it’s very simple. Does this truck have HEI or breaker points? If it has points, you need to set the gap, dwell, and check the timing (should be around 8 degrees BTDC at idle, vacuum advance disconnected and plugged), and a new condenser wouldn’t hurt (is that the ceramic piece you referred to? Or a ballast resistor?). If it was my truck, I would stick an HEI distributor in it and never have to worry about points again. Most Chevy nuts have half a dozen or so of those things lying around, so one shouldn’t be hard to find if you go that route.

Next up is fuel. You said you replaced the carburetor, but I am a little confused since you mentioned both Holley and Quadrajet. Rochester made the Quadrajet, which was commonly used on these trucks, and Holley is a completely different brand most commonly found on Fords. These engines usually came with a 750 cfm Quadrajet, which works very well as long as it is set up properly. I’m going to assume you currently have a Quadrajet on this engine. If in doubt, your best bet is to find an old mechanic who knows a lot about this carburetor because they can be temperamental. The strongest fuel related suspect on my mind, though, is the choke, and you may be able to check this out for yourself. If it’s not opening up all the way, you will have problems like this as the engine warms up. Check for mechanical binding in the choke linkage/fast idle cam and make sure you have power to the electric choke coil, if so equipped (most Quadrajets have an electric choke). If your truck did not originally have an electric choke and your current carburetor does, you need to run a source of switched power to it so it will open the choke as the engine warms up.

Has anyone checked the timing chain…to see if it’s jumped a sprocket or 2??

I wholeheartedly agree with Mark’s post, however in order to check the vacuum you’ll need to get it started first.

How much water was in the gas tank? Water is heavier than gas, and if it’s significant the fuel pump’s pickup tube could be sitting in water rather than gas. That’d mean the fuel lines, carb, and pump will be also filled with water at this point.

Will it start using starter fluid? That’d be a good clue that it’s probably fuel related.

I just now saw the part in the post that says the truck won’t start or turn over. Has the battery been drained or starter burnt up from attempts to start it? If it’s the battery, it can be recharged.

Since water in the gas tank is a suspect, I thought I’d mention this method of determining if that is the problem. You will need a couple of gallon jugs and some rubber fuel hose. Drill a hole in the bottom of one of the jugs the right size to accommodate the rubber hose as a tight friction fit. Jam it in there, fill the jug with known good gasoline, then plumb that into your fuel inlet of the carburetor. Use more rubber hose to plumb the fuel pump outlet into a gas can or other receptacle to catch whatever the fuel pump will be pumping out, be it gasoline, water, or whatever. Keep the jug full of gasoline higher than the float bowl of the carburetor (it’s now a gravity fed fuel tank) and see if you can get the truck to start. If it will run on this, and the fuel pump is supplying good volume and pressure, your fuel is contaminated. You can also use this method to run the fuel pump to drain the vast majority of the contents of the fuel tank if need be, so long as you have containers to keep filling up until the tank is empty.

mark9207 (1st post)- yes, it is a Quadrajet, yes it was the resistor ballast, no it doesn’t have an electric choke, actually has a small choke box with coil spring beside the mounted to block next to carb. HEI sounds like a good suggestion, point taken.

MikeInNH - we did NOT check the timing chain, but that is a good suggestion.

the same mountainbike - Once the tank and lines were drained, we found about 1 liter of water. After draining and refilling tanks with fresh gas it ran fine for several trips and again began to show the same symptoms afterwards.

mark9207 (2nd post) - haven’t checked the starter lately, battery confirmed charged. Drained tank and lines and refilled with new gas.