73 pickup refuses to run correctly

I have a 73 c-10 pick up with 350 engine.
It just refuses to run correctly,& am at wits end trying to figure out what to do or try next to solve its issues.

the truck will sit and idle very well after it has completely warmed up, however getting it there is sometimes a challenge as it seems to load up really easily with fuel. The real problem though is that while accelerating, it acts like it doesn't know what to do with the fuel. It sputters, hesitates, and chokes down & sometimes will back fire thru the exhaust.
The truck can be driven (barely) and pulling a trailer or driving with a load is out of the question since there is no power what so ever

I have had it to 3 different mechanics . all checked the compression and said that while its not perfect - it is within reason. 2 mechanics say that the timing is ok. I've had one person to tell me that the valves were burnt causing the back firing, but if that was the case then the compression test should have shown that the valves were not seating properly (if im not mistaken).

The first mechanic told me that the carburetor that was on it was washing the cylinders with fuel and fouling the plugs. So the remedy was supposedly to get a lower cfm carb replacement. He put on a new not reman. 650 cfm (i think)Edelbrock carb., changed the ignition over from points to HEI Distributor -(with new coil , rotor, and cap - all gm parts) , replaced the plug wires with ac delco wires, upgraded the plugs (also ac delco) to accomodate the hotter ignition, and double checked the timing.
All of this improved the performance like night & day difference for a while, but now im back at square one and it seem no one can get the performance back.
the last mechanic says that edelbrock is no good and i should have put on a Holley carb.
I can tinker with it a little and get it running some better, but the next time it is started after it has cooled down its back to its old tricks.

Anyone out there have suggestions of what to check next to possibly solve the problem? Are these mechanics missing something??

Thank You in advance for any help you can share with this!

How many miles on the 350? And unless the carb you got is faulty or defective there is nothing wrong with it edelbrock makes a good carb. Have you checked your vacuum lines and the choke settings?

Im unsure of an exact mileage for the engine, since it was rebuilt/swapped, a few years back. An educated guess would be approximately 80K - 90K.

I personally dont see anything wrong with edelbrock - that was just a mechanics opinion i got.

The mechanic that installed the edlebrock carb set the choke at that time. (by the way it is an electric choke) He claims it is working as it is supposed to.

As for vacuum leaks, i have not been able to find any and none have been mentioned by the mechanics either

Camshafts can be suspect on the small block, they wore lobes routinely in the old days. I would do a leakdown test to confirm valve condition first, a compression test is too general. Then I would pull the valve covers and make sure all the valves are actuating properly, the mechanical condition of the engine is your prime concern. If all is ok, confirm proper initial timing and advance, then make sure the timing chain is not worn. Check the vacuum at idle and speed also. Did the engine ever run ok, how and when did this start?

Yes it did use to run ok, The problem has gotten progressively worse over time and i was told by mechanics that the problem was with wear in the carburetor body allowing excess air to be sucked in and was flooding the cylinders causing fouling of the plugs. So we replaced the carb with new to eliminate that.

After replacing the carb and doing an upgrade to HEI it ran very well and got excellent fuel milage, - but all of a sudden that changed and now im back to square one and the mechanics cant find what the problem is.

Thank you for your suggestions i will follow up with those and see what i come up with.

Unless you have a trust worthy mechanic that you have known for a while I would not take absolute stock in what the say. As far as where you stand now I agree with Maxwedge double check your valves, timing and definitely your vacuums. Good luck buddy And keep us posted!

Well here's an update on what was found to be the problem.

After some more checking for vacuum leaks (none found) and removing the valve covers to see if all the rockers were functioning to try and eliminate cam lobe wear as the cause, I was lucky to find an ex-chevrolet dealer mechanic that is now working out of his own garage at home.

He found more in 30 minutes than the other 2 mechanics did on multiple visits and were still scratching their heads as to what was wrong.

The first idiot that replaced the carburetor & upgraded the ignition to HEI spliced the electric choke & the coil wire to the distributor into the ignition field wire that goes to the alternator.
This was causing the coil to only be supplied just under 9 volts instead of 12.
The plug spark was orange and couldn't ignite the fuel well enough for it to run.
The second problem was found after he got the spark nice and blue to where it was properly igniting the fuel - the fuel pump was so weak it was barely supplying any fuel to the carb ( the mechanic said the vacuum from the carb was probably the only thing pulling the fuel up to the bowl)

He double checked the timing - TDC & valve position /versus rotor pointing to the corect position and found that the distributor was installed 90 degrees off from the correct position.

He rewired the choke and distributor to their own circuits so the correct voltage would be supplied to each.

Everything else checked out good and the truck is running like new again.

Right on glad to hear it up and runnin'