Engine bogging under throttle?

[JohnKimble]

Hello,

My question is in regards to my 1985 Chevy k10 350. Today I finally pulled it out of storage, it's been sitting for over a year (sta-bil in the fuel tanks).

I hooked up a new battery and it fired up without issue. After a minute or two I began to give it some gas (while in park). If I slowly depressed the gas pedal, the engines sounded fine. If I quickly hit the gas to the floor, it would bog and stall out. If I slowly increased the RPM's, then quickly floored it, it would bog and hesitate.

I let the engine idle for about 10-15 minutes. I tried hitting the pedal to the floor, and it roared without issue. I'm not sure if anyone has any idea as to why after 10 minutes, the truck appears to be running fine. Could this have anything to do with a new battery and the ecm being calibrated?

I'm not sure if that even makes sense in a 30 year old truck, but I really couldn't think up any other reasoning.

[TrailerTrash]

makes perfect sense to me. old engines need to be warm to run best. my 79 wants to sputter and die till it gets warmed up then it runs awesome.


has it been swapped to electronic fuel injection?

[JohnKimble]

Nope, it's all stock. It does have the CA emissions package, so I'm thinking there's some computer calibration that needed to be done.

[E.D.75GMC]

My 75 has been doing this as well actually. It hadn't been on the road for a few months over the winter. I put stabilizer in the tank as well and filled it to the top and started it up and ran it to operating temp once per week. Last week I renewed the plates and started to drive it again and I'm having the same problem as you. Isles fine and runs well under light throttle but when you stab the gas to merge onto the highway or anything that requires quickly speeding up it starts to bog out and lose power. Haven't been able to figure it out, nor could the shop I took it to. I tried carb cleaner and fuel system cleaner in the tank to no avail.

[minitrail]

What kind of carb do you have? I had the same problem with my truck and it ended up being the accelerator pump. Mine was swapped out a long time ago to an edelbrick 1406 but I am guessing the Rochester's have the same system if sorts. It's essentially a rubber plunger that squirts extra gas into the carb on acceleration. Open the butterfly and look down in with the truck not running. Move the linkage as if you are flooring it and you should see some gas squirt in. If that rubber plunger is damaged the gas will pass back up through the seal rather than into the carb. Not sure that's it but I would check there especially if it was fine when put away.

[rich weyand]

^^^ This.

When the throttle is snapped open, air rushes in faster than the fuel circuit can speed up. This results in a super-lean condition and the fire goes out. Fuel injection systems have no problem dealing with this, because they are reading the mixture and adjusting it in real time. Carburetors deal with it by using an accelerator pump to squirt a calibrated amount of raw gas into the carb throat. If the rubber gasket around the accelerator pump wears or age hardens and therefore doesn't seal, you will get a bog on quick throttle openings.

When you slowly open the throttle, it's not a problem, because the fuel circuit doesn't fall as far behind the air flow and the super-lean condition does not exist.

Replacing the piston on the accelerator pump is pretty easy and fast, and will remove this as a possible problem. Should be done occasionally (~5 years) anyway.

[LBJ]

Sounds like the old "sucking air" in the fuel line or just needs a new gas cap. The sucking air can come from the rubber hose between the fuel pump and the chassis which can have a hole in it and yet not cause a problem all the time. Also, the gas cap can be clogged and not venting which can give you one heck of a time figuring that one out. New gas caps are cheap. Fuel line is even cheaper. Or, may need a new fuel filter. May be something else entirely, but always check the simplest items first.