Backfiring under load

[silverscottsk10]

Truck has a bad issue with backfiring under load
Around 2-2500rpm
If I slowly creep into the range it won't do it
But stomping it it will either backfire like a machine gun or totally miss on firing at all and falls on it's face
It's gotten old and bout gotten me hit a few times
New timing chain is on the way along with an assortment of gaskets
And after messing with it I'm bout to just gut and rebuild it after fixing one thing another tends to appear
This engine has it out for me

 

[rich weyand]

Happened to me. The distributor was not clamped down tight and was dragged retarded by the rotor shaft.

Check the timing.

 

[silverscottsk10]

The distributor is tight
I thing my chain is just so loose that when it's snapped tight it may screw up my timing

 

[bucket]

...backfire like a machine gun...

That there sounds like the cam has wiped a lobe, if it's backfiring out the intake.

 

[77 K20]

I'd agree with bucket. That is what mine did with a flat lobe or 2. Mine would backfire around 3000 rpm.


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[rich weyand]

The distributor is tight
I thing my chain is just so loose that when it's snapped tight it may screw up my timing

Did you actually check the timing, not simply assert what you think is true?

The reason I suspect base timing is that the problem you are having is vacuum dependent, not RPM dependent. When you get on it and lose vacuum, you also lose the vacuum advance. If it is way off retarded, the vacuum advance may make it work OK at low throttle settings, but when you get on it and dump the vacuum, you lose the vacuum advance and see only base timing. If you creep up on it, as you say, it works because with the vacuum advance pulled in, the timing is at least advanced enough to make it run, though not well.

 

[jeffro308]

Truck has a bad issue with backfiring under load
Around 2-2500rpm
If I slowly creep into the range it won't do it
But stomping it it will either backfire like a machine gun or totally miss on firing at all and falls on it's face
It's gotten old and bout gotten me hit a few times
New timing chain is on the way along with an assortment of gaskets
And after messing with it I'm bout to just gut and rebuild it after fixing one thing another tends to appear
This engine has it out for me

Could it be fuel delivery? My old 69 leans out sometimes when I romp on it. I can also ease into it and prevent the backfiring.

 

[silverscottsk10]

Chain is slapping my front cover
Distributor isn't but maybe a month old
And if I advance it anymore truck diesels out and takes forever to die
If i retard it any more it barely revs before it starts missing
The chain is bad and has been for awhile
And it doesn't backfire through the intake
It's exhaust both sides
Kinds sounds like a jake brake

 

[rich weyand]

What is the base timing set at, in degrees? Where is the vacuum advance connected? What kind of distributor is it?

 

[silverscottsk10]

I'd have to check degrees
I just found the spot to keep both from happening too bad
It's connected to far left port of edelbrock 1406 and ac delco distributor

 

[rich weyand]

When you say far left port, is that your left or truck left? Better yet, driver's side or passenger's side?

 

[silverscottsk10]

Pass side exhaust

 

[bucket]

For future reference, the driver's side is always known as the left side (and of course the passenger side would be the right). That's the automotive industry standard (North American)

 

[rich weyand]

Vacuum advance tube from the distributor should connect to the driver's side port (manifold vacuum) on the Edelbrock 1406 unless the engine is equipped with a working AIR pump. Connecting it on the other side will make it idle poorly.

Note legends on those ports.

You must be registered for see images attach

 

[silverscottsk10]

For future reference, the driver's side is always known as the left side (and of course the passenger side would be the right). That's the automotive industry standard (North American)

It tells you that in the manuals
Suppose to say it as if you was sitting in drivers seat