Popping through carb

[dotman]

Recently had the heads on my 1969 440 engine in my 1970 GTX redone due to a piece of carb linkage falling down into the engine and taking out 3 cylinders. Now after reassembly I am experiencing a popping through the carb( Carter AVS) when the secondaries kick in. Not a single pop like a timing issue but a series of pops like a pack of firecrackers until I back off the throttle and get out of the secondaries. I had the carb redone the end of last year by Harmons. I tried messing with the timing-No change. I checked fuel pressure. 3.5 PSI at carb through the entire RPM range. Car ran good before the failure and I had the heads redone.Maybe a intake leak?? I checked vacuum at carb and at the intake port and they both seem to be about the same 20 hg with a slight fluttering of the needle at idle. Any thoughts??

 

[1badstroker]

For starters the fuel pressure should be 4 1/2 lbs at min. per an old mopar service book for a 1969 440 hp. The 440 hp in 1968 required 6 3/4 min. and the 1970 440 hp required 7 to 8 1/2 lbs of fuel pressure. Check the cam to make sure it is not having an issue like premature wear. ( a lobe going flat )
It may not pop under normal driving until there is a load put on the engine.

 

[HEMI-ITIS]

Sounds like a lean condition,does it pop soon as you floor it or as the rpm's come up??

 

[Meep-Meep]

Does the secondary air door have reasonable tension? I'll agree it sounds like it's going lean. Just to check the obvious but is the PCV hose hooked up or any other open ports? A poorly seating intake valve can do that as well, but hopefully it's not that. I would think 3.5 PSI should be plenty for a mild to stock engine. I'm running 3-3.5 PSI on my 351C Ranchero and it's fine.

 

[dotman]

It seems to pop as soon as you floor it and the secondary air door opens up. The door seems to have tension on it. I did have to remove the door to replace the piece of missing choke linkage, but I made sure the spring did not unwind. The PCV valve is still hooked up and is the one that was on the car before the heads came off. I did a compression test and all the cylinders are pretty close to each other. between 145-160 in each hole. I am thinking of changing the intake gasket again just to rule it out. Not a hard job anyway. I used the steel intake gasket and aircraft sealant on both sides of the gasket.

 

[HEMI-ITIS]

Verify accelerator pump is shootin' and fuel bowl levels are right:grin:

 

[dotman]

Well mystery solved. Was talking to one of the guys in the shop today about the problem and he also told me to check the camshaft for lobe failure. Some of the older state trooper cars, he used to work on, had identical symtoms. Sure as s%#t, 1 lobe rounded with two more on the way. I never would have guessed that. Don't know why a well seasoned cam would go bad like that but looks like I will need to check things out better this weekend and determine whether a new cam goes in or the engine comes out and gets rebuilt over the winter. All that metal had to go somewhere!!

 

[1badstroker]

Stay with oil that has zinc even after the cam/motor is seasoned/broken in. There is so much junk oil out there. I am running the valvoline VR from napa at 4.79 a quart. That is as cheap as I have found it in my area. Good luck.