Truck feeling like it is under load?

[Eastonfrench]

So I pulled a 1980 K10 (350 V8) out of a farmer's barn and have brought it back to life. Ever since I started driving it, I've noticed it has really poor acceleration. My dad, who grew up driving the same truck, assures me that it isn't near as powerful as it should be.
From a stop, as well as from when rolling, if i punch the gas, it behaves as if i am slowly pressing the accelerator, and sometimes even stalls out for a second. it eventually gets up to speed, but doesn't really throw you back in your seat.
Ive replaced the following in an attempt to eliminate possible culprits:
Cap/rotor/plugs/wires
Fuel Pump
Accelerator pump
Carburetor rebuild
Air Filter

I ensured the secondary air flaps are opening as well, and I am now out of ideas. What else should i check?

[reed85]

U could do a compression test and wat kind of trans do u have

[bd]

Did you replace the fuel filter?  Check the ignition timing and make sure the mechanical and vacuum advance mechanisms are working correctly.  How many miles on the engine?  A 35 year old truck could have a lot of wear.  Engine compression and timing chain should be checked along with the condition of the harmonic balancer.  Tire diameter and gearing will also play a roll.

[Eastonfrench]

Thanks for the replies!

It's an automatic tranny

I set the timing to factory specs. The vacuum advanced seems to be working (when I open the throttle the timing mark advances).

I did change the fuel filter, to no avail.

I haven't done any compression testing, but the truck only has 80000 original miles, and they were mostly to town and back at about 35 MPH. (An old farmer owned it).   

I'm not sure how to check the harmonic balancer (or even what it is). Or a better way to check the mechanical advance?

[rich weyand]

I would at least try it on direct manifold vacuum, without all the extra crap in the way.  That's all pollution nonsense.  How much of the pollution nonsense is built into the ECM is another question.

Going to manifold vacuum, you should lean out the idle, and advance the base timing from factory specs.

[zieg85]

I'd like to throw my $.02 in and suggest the catalytic converter may be plugged

[Eastonfrench]

Zeig,

Is there any way of checking the Cat? This may be irrelevant, but theres plenty of exhaust gas coming out of the tailpipe. COuld the Cat still be plugged? Any Suggestions?

I am going to take a look at the Mechanical advanced as well as the Cat when i get off work this afternoon-Updates to come

[zieg85]

Not sure, I just take them off temporarily and try it.  When clogged or nearing being clogged they get really hot...  When sitting there at idle, does it rev good?  Also do you have a stock air cleaner?  Is it a quality air filter or some bargain brand.  I've seen cheapo's manufactured with the filter element in backwards.  They look clean but are clogged.  If you have a stock air cleaner, take the filter out for a quick test.  If the catalytic converter is fine and it isn't the air filter more than likely it sounds like timing.  A sloppy (worn) timing chain would also cause this issue. 

[bd]

...The vacuum advanced seems to be working (when I open the throttle the timing mark advances).

...I'm not sure how to check the harmonic balancer (or even what it is)

...[Is there] a better way to check the mechanical advance?

Mechanical advance is tied directly to engine RPM.  Remove the vacuum hose from the distributor vacuum advance.  Being very careful to avoid the fan and belts, throttle the engine while watching the timing mark with a light.  The timing mark should transition smoothly with RPM change, both up and down, beginning about 1,200 RPM.  Then with the engine running at 1,500 - 2,000 RPM, reconnect the vacuum hose to the distributor vacuum advance - the timing should increase.

The harmonic balancer is the cast iron hub on the front of the crankshaft that bears the timing mark.  The outer ring of the balancer is vulcanized to the hub through an elastomer band.  With age and use, the outer ring can gradually rotate around the hub throwing off the timing mark.  For examples of how to check the harmonic balancer and the timing chain, read through Re: Not 100% what's wrong here and Re: 86 C10 Loping.

To check for a plugged exhaust (cat, muffler or collapsed pipe), temporarily separate the exhaust ahead of the cat and road check for a seat-of-the-pants improvement.  Alternatively, if the engine has a smog pump or O₂ sensor, an AIR injection check valve or the O₂ sensor can be temporarily removed from the exhaust and a 15 - 20 PSI pressure gauge plumbed into the resulting hole to measure exhaust backpressure with the engine running, which should not climb above ~1.5 PSI at 3,000 RPM.  You could accomplish the same thing by drilling a small hole in the headpipe and plumbing a gauge there; then plug the hole with a screw when done.  A less direct method (more interpretive) is to use a vacuum gauge on the engine while accelerating under load.

[Eastonfrench]

Wow. Thanks for the input guys.

So after work, I popped the distributor cap off. The mechanical advance is spotless (theres definitely no crud keeping it from engaging).

I do have the factor breather on, with a new air filter, but I will try taking it down the block without a filter here real quick

I am going to see how hard its going to be to pop the Cat off, and give it a road test.

I am really hoping it isnt the timing chain. I cant imagine thats an easy replacement.

Thanks again...Ill be sure to post when I try some of these things.

[Eastonfrench]

SO.

I went and took it around the block with the air filter off. No change, so I think it is safe to say it is getting enough air.
when I got home, I checked the Cat, and what do you know? it was STEAMIN hot. Much hotter than it should have been after a two minute drive.

So I cut it off. The whole exhaust from the cat back. Now she sounds awful ( I knew this would be the case, but it needed a new exhaust anyways), and still behaves odd. It did seem to pick up a little horsepower, but from low rpms if you stomp on it, it stalled out for a second or two still.

So the issue is certainly not exhaust, and certainly not air. Where should we go from here fellas?

Thanks again. I really appreciate the help trying to restore this thing.

[1967KaiserM715]

Check compression, I  almost can guarantee it is low, by stuck rings from sitting, two ways to fix, keep running or do a re-ring job

[Eastonfrench]

Update:
I bought a piece of exhaust union and hooked the muffler back up (its just 2 foot shorter of an exhaust system). Once i hooked it up, I think the truck is a LOT better. It must like a little backpressure. I will let yall know more after i take it on a long drive tomorrow. Cheers.

[Eastonfrench]

Hey guys. I've got a 1980 k-10 with a 350 and a quadrajet. I've got an acceleration problem. When you start the truck up, and drive away, all is fine. But if I give it any more than half throttle, it falls on its face. Sounds like it dies but if I let off the gas it fires back up. I can ease into the gas and it will take full throttle, but I have to really baby it.
I've noticed that if I drive 15 miles, it tends to be less extrem (it lets me give it more throttle before stumbling). I really want to get this thing tuned in so that I can put the pedal all the way down from a stop.
I've replaced the fuel pump and filter. New plugs wires cap and rotor within the last 6 weeks. Removed the cat. Rebuilt he carb and put a new accelerator pump, needle and seat in. Timing is set on 10 degrees initial, and the vacuum and mechanical advance both appear to be working. I set the choke by feel, but it appears to be fully disengaged once it warms up in the driveway (the flap is totally vertical)

I checked for a vacuum leak a couple weeks ago by spraying carb cleaner but I didn't find anything.

Other indicators that may not be related: I get a small puff of smoke when starting it. In park, she revs up awesome, but kind of cackles out of his exhaust at high RPMs.

[LSXCHEVY]

IMO... too much gas or timing is off.. what fuel pressure carb running?.. I would advance timing till it pings under load then back off a little.