Engine starts but back fires through carb. exahaust valve rocker arm was off of the pushrod. pushrod is not bent neither is the valve. does it have a hydrualic lifter?

the high lift cam has no compensation and so the valve retainer bottomed out causing the rocker to slip sideways and bend the push rod
you would have been better fitting a prolonged duration cam rather that a high lift for the following reasons
1 --- you can used standard rocker gear
2 ---there is no valve bounce at high rpm
3 --- smoother air flow in the inlet manifold so there is not such a stop/ start action when rpm is low
4--- less wear on cam followers and cam lobes
cam shafts are all about open duration so longer open with smaller lift is better than the same duration with a fast up and down action

It sounds like your tolerances on cams, etc, inside the engine are out of spec causing this problem. I would do a complete teardown of engine to properly diagnose.

I’m happy to assist further over the phone at https://www.6ya.com/expert/layne_0fccff498c319c32

Back off on all the rocker arms and check to make sure you didn't bend any push rods then make sure you are starting on #1 Cylinder and readjust, when it starts you can finish the adjustment by backing off rocker arm nut till you here it TICK than tightentill TICK IS GONE. I do not have info on the fireing order for primary adjustment but you should be able to find on line complete instructions, Go to ASK.COM and ask for Chev 350 Valve Adjustment their are several to choose from and even YOUTUBE Videos on it.

most common ticking noise under the hood is from the valve train [burnt,bent,sludged pushrods]--burnt,bent,damaged valves---[loose,damaged rocker arms]--burnt,flat spot,sludged camshaft----sludge build up in engine-low oil pressure ---need oil change-other can be bad idler pulley,alternator bearing going bad

Hi there:

Rocker Arms & Pushrods

Removal & Installation

3.1L & 3.4L Engines
Left Side

1. Before servicing the vehicle, refer to the precautions section.
2. Drain the cooling system to a level below the coolant pipe on the front of the engine.
3. Remove or disconnect the following:
   NOTEKeep the pushrods in order. Intake pushrods are 5 3 / 4 inches long and exhaust pushrods are 6 inches long.
   
   
   Negative battery cableSpark plug wiresHeater bypass pipePositive Crankcase Ventilation (PCV) valve and hoseRocker arm cover
   
   
   Rocker arms and pushrods
   

To install:

1. Lubricate all the valvetrain components with engine oil.
2. Install or connect the following:
   
   Pushrods and the rocker arms. Torque the bolts to 24 ft. lbs. (32 Nm).Rocker arm cover using a new gasket. Torque the rocker cover bolts to 89 inch lbs. (10 Nm).PCV valve and hoseHeater bypass pipe. Torque the screw at the water pump to 106 inch lbs. (12 Nm), the bolt at the cylinder head corner to 18 ft. lbs. (25 Nm) and the nut to 18 ft. lbs. (25 Nm).Spark plug wiresNegative battery cable
   
3. Refill the cooling system.
4. Start the vehicle and verify no leaks.

Right Side

1. Before servicing the vehicle, refer to the precautions section.
2. Remove or disconnect the following:
   NOTEKeep the pushrods in order. Intake pushrods are 5 3 / 4 inches long and exhaust pushrods are 6 inches long.
   
   
   Negative battery cableAlternator bracket on 2005 modelsSpark plug wires from the spark plugs and the upper intake plenum wire retainerPower brake booster vacuum pipe from the intake plenumAccessory drive beltAlternator, if necessaryIgnition coil assembly and Evaporative Emissions (EVAP) canister purge solenoid as an assemblyRocker arm cover
   
   
   Rocker arms and pushrods
   

To install:

1. Lubricate all the valvetrain components with engine oil.
2. Install or connect the following:
   
   Pushrods and the rocker arms. Torque the bolts to 24 ft. lbs. (32 Nm) plus an additional 30 degree turn.Rocker arm cover using a new gasket. Torque the rocker cover bolts to 89 inch lbs. (10 Nm).Ignition coil and EVAP solenoid assemblyAlternator, if removed. Torque the bolts to 37 ft. lbs. (50 Nm).Accessory drive beltPower brake booster vacuum pipe to the plenumSpark plug wiresNegative battery cable
   
3. Start the vehicle and verify no leaks.

Hope this helps.

With the Engine in the number 1 firing position, adjust the exhaust valves for cylinders number 1, 3, 4, and 8 and the intake valves for cylinders number 1, 2, 5, and 7.
Turn the valve rocker arm nut counter clockwise until the valve lash is felt in the valve pushrod.
Turn the rocker arm nut clockwise until all of the valve lash is removed (zero valve lash).
Zero valve lash can be felt by moving the valve pushrod up and down between your thumb and forefinger until there is no more up and down movement of the valve pushrod.
When all the valve lash is removed, then turn the valve rocker arm nut clockwise 1 additional turn (360 degrees).


With the engine in the number 6 firing position, adjust the exhaust valves for cylinders number 2, 5, 6, and 7 and the intake valves for cylinders number 3, 4, 6, and 8.

Follow the same steps as above.

1. For the 4.3L engines which are equipped with screw-in type rocker arm studs with positive stop shoulders, tighten the rocker arm adjusting nuts against the stop shoulders to 20 ft. lbs. (27 Nm) on 1994-96 models and 18 ft. lbs. (25 Nm) on 1997-99 models. No further adjustment is necessary, or possible.
   
2. For most 4.3L engines which are not equipped with screw-in type rocker arm studs and positive stop shoulders, properly adjust the valve lash. For details on valve lash adjustment, please refer to the procedure in Routine Maintenance . (see below)

4.3L Engine

The 4.3L engines may be equipped with either of 2 rocker arm retaining systems. If your engine utilizes screw-in type rocker arm studs with positive stop shoulders, no valve lash adjustment is necessary or possible. If however, you engine utilizes the pressed-in rocker arm studs, use the following procedure to tighten the rocker arm nuts and properly center the pushrod on the hydraulic lifter:

1. To prepare the engine for valve adjustment, rotate the crankshaft until the mark on the damper pulley aligns with the 0? mark on the timing plate and the No. 1 cylinder is on the compression stroke. You will know when the No. 1 piston is on it's compression stroke because both the intake and exhaust valves will remain closed as the crankshaft damper mark approaches the timing scale.

Another method to tell when the piston is coming up on the compression stroke is by removing the spark plug and placing your thumb over the hole, you will feel the air being forced out of the spark plug hole. Stop turning the crankshaft when the TDC timing mark on the crankshaft pulley is directly aligned with the timing mark pointer or the zero mark on the scale.
The valve arrangement is as follows:



E-I-I-E-I-E (right bank-front-to-rear) E-I-E-I-I-E (left bank-front-to-rear)

1. With the engine on the compression stroke, adjust the exhaust valves of cylinders No. 1, 5 & 6 and the intake valves of cylinders No. 1, 2 & 3 by performing the following procedures:
   1. Back out the adjusting nut until lash can be felt at the pushrod.
   2. While rotating the pushrod, turn the adjusting nut inward until all of the lash is removed.
   3. When the play has disappeared, turn the adjusting nut inward 1 3 / 4 additional turns.
   
   
2. Rotate the crankshaft one complete revolution and align the mark on the damper pulley with the 0? mark on the timing plate; the engine is now positioned on the No. 4 firing position. This time the No. 4 cylinder valves remain closed as the timing mark approaches the scale. Adjust the exhaust valves of cylinders No. 2, 3 & 4 and the intake valves of cylinders No. 4, 5 & 6, by performing the following procedures:
   1. Back out the adjusting nut until lash can be felt at the pushrod.
   2. While rotating the pushrod, turn the adjusting nut inward until all of the lash is removed.
   3. When the play has disappeared, turn the adjusting nut inward 1 3 / 4 additional turn.
   
   

He meant bent valve. you are looking at a head job. sorry but these are interference engines.
In fact I believe it has an overhead cam right? If so then there are no pushrods. Generally all a bent pushrod does is leave the valve closed.

it sounds like the valve lifter may have collapsed try an engine flush if this doesnt help you will have to replace the lifters

If it is a push rod or a loose rocker arm it wouldnt be rattling it would be ticking or knoking.