'72 Truck Dying on Incline

[capturedlive]

My '72 GMC Sierra 2500 (402 cu. in.) has recently been giving giving me a pretty hairy problem. At one point on the freeway where there's an incline (and no shoulders) it starts losing power. Punching the gas only makes it worse, and it's only when I release the gas and ease back into it that I have the best luck of getting over the hill. Then, once I'm over and either going downhill or on level road it's fine. However, the other day during rush hour, I completely lost my power and had to stop, put it in Park, and after a couple of attempts, roared the engine back into life and was able to resume (amidst horns and cursing).

I tell mechanics the problem and they scratch their heads. It might be the filter in the gas tank... or it might be the carb... or it might be the points...

Before I take it in, I was hoping this issue might be familiar to someone on the forum. I really don't want to fund a slew of services without a firm resolution.

Thanks.

[Shyguy]

Sounds like it could be many different things causing this. One could be the sock in the tank collapsing cutting off the flow of fuel. Another could be cracks in the two places where there are rubber fuel lines on the suction side of the pump. The rubber hose on the suction side of the fuel pump could be collapsing. The fuel filter in the carb could be plugging. Also the fuel pump could be giving out.

Before I replaced the fuel pump I would check all the other stuff.

[TBONE1964]

My first thought is float level in the carb. If the float has a hole in it, or it is stuck half way down in the bowl, it will not let the fuel fill the float bowel which has the gas required to let the accelerator pump give a shot of fuel. When the truck is on an incline, it is not supplying fuel to the accelerator pump.

Does that make sense?

[darush01]

I agree with what was mentioned above, if you have access I'd change the carb to see if that helps but if your not like me and sitting on a ton of parts then I'd check the hoses on the pump to see if they are soft and collapsing and the other things mentioned above because rebuilding a carb is expensive and if you don't know what your doing I don't recommend trying it I couldn't get mine set right at all
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[Hawghauler]

Does it do it only on an incline? Does it do it immediately on the incline or only after climbing for a while? It could be something other than fuel. If it does it only on an incline and not when you are getting on it on the flat, it could be the ignition power grounding out and reducing power to the coil. If it only does it after climbing for a while, then it most likely is fuel related. i.e. float, or filter causing starvation. Try flooring it on the flat as long as you dare, and see if it happens then. If it's fuel related it will happen then as well. I've had ignition power do strange things with a broken or grounded wire. If you can't replicate it on the flat or downhill, try disconnecting the keyed hot wire to the coil, running a hot wire to the positive on the coil and bypassing the main keyed wire and go up a hill to see if happens then.
I had a Firebird that would almost stall, only on left hand turns, I tore the carb apart, replace fuel pumps, filters, etc with no results. When I finally hot wired it, I found that was the problem. I had a Chevelle that on inclines would suddenly just die, then before I could do anything, it would suddenly fire again and blow off both mufflers. The Firebird was grounding out, and the Chevelle had a broken wire that looked fine.
Good luck, and let us know how it fares.

[pritch]

You don't happen to have one of those Holley Eco-miser carbs do you? They'll do that same thing.

[capturedlive]

Thank you for all your input; I'll make a list from them and bring it with me to the shop. No, I'm not sitting on a pile of parts, nor have a chunk of change sitting in the bank for moments like this, so I'm hoping it doesn't involve replacing the carb. And no, I don't believe this is a Holley Eco-miser carb. I'll report back when I learn what exactly is going on. Thanks again!

[Boog]

I had similar issues with one of my old trucks years ago. It got to where it almost wouldn't pull itself at all. Mine turned out to be a siezed centrifugal advance. It was barely moving at all. I had to completely disassemble the distributor to clean the inner shaft. It worked fine after that.