Hello,

Thanks for any input you can give... I have a 72 Cutlass with a 1978 350 rocket in it. I have had it over at the shop recently and had the carb rebuilt, new gas tank and a tune up... Why is it still popping through the carb under heavy acceleration?

Thanks,

Greg

 

Does it hesitate (like it is wanting to die) then pop? If so it sounds like it is runnin too lean. Was it checked for vacuum leaks? Was the timing set right?
Did the carb guy adjust it all right including the accellerator pump?
Since it is a 78 motor, I assume the carb was rebuilt to 78 specs. Is the EGR valve working right, or stuck? They have a tendency to clog up and jamb open or closed.
Just some first thoughts...

 

Was it popping prior to all the work you just had done??

 

Was the plug wires replaced when it had a tune up?

 

Could be a broken intake valve spring. Is it ticking?

 

burnt valve?

 

I had one do that when a lobe on the cam was worn down.

 

x2

 

Two of the plug wires out of sequence at the distributor. check it out

 

Thanks guys,

The car was popping before the work was completed; it seems to do it more when cold. It does run better after the work was done as far as initial start up and idling. My mechanic (who is a gear head) suggested possibly a flat cam or something in the valve train as well.
I plan on rebuilding the motor this winter or finding a suitable replacement, just wanted to get the car on the road to see what else may be wrong. I drove the car home from the shop (approx 20 miles) and handles great, so I need to pay attention to the motor. Any other suggestions please feel free to add on.

Thanks again,

Greg

 

x3

 

Check your carburetor's accelerator pump/ pump shot first.
No matter which carb, look down the throat, hit the throttle, and you should see 2 nice streams of gas going down into the manifold. If not, make it do so.
That is the first thing I look for, before I'd go to the other items mentioned on this thread, although Rob Young did mention it.
Backfire through the carb is a lean pop. When you hit the gas, you need FUEL, and a bunch of it.
Carb accelerator pump, goes a long way here.

Carb rebuild is NOT part of a tune-up.

JMO
Jim

 

Thanks Warhead,
I actually did the tune up myself and had the shop do the rest (due to their lift and carb boil tank capability). They replaced the accelerator pump when completing the carb rebuild, but I will check what you recommended. When I pulled the fuel filter there was allot of gunk on it and found some buildup in the tank, and that is why I replaced everything from A to Z to eliminate that problem. I will keep you posted regardless.

Thanks,

Greg