[iburke]

Ok big block guru's As you know I have a 71 454. Having a little trouble. When idling if I go half throttle I get a pop back thru the carb. while driving and I accelerate. I get a pop pop pop until I reach a cruse speed.

I have checked timing, valve adjustment, carb(not running lean). The heads were redone less than 1000 miles age. compression is 185 to 190 all cylinders. Idles good, starts good. The plugs show if any thing all cylinders are running a little rich....?????:huh:

 

[jjwvette]

Did you check the distributer cap or coil:huh: It's been a long time since I've had to do any work on cars since the new ones have all electronic gismos:laughing:

 

[iburke]

Yep been through the points dist. coil, plugs. thanks.

 

[matchframe]

One time I had the same symptoms and it ended up being a cracked distributor cap. Maybe that could be your problem.

 

[68BB]

Sounds to me like the vacuum diaphram needs replaced in your carburetor.

 

[rtj]

A worn out timing chain can contribute to the engine running poorly.

 

[iburke]

Thanks will double check the carb and dist. Hoping not to have to open up the engine. Do you think a flat cam lobe coould cause this?

 

[Fred Mann]

What was the last thing you did to the engine before this started to happen?

 

[iburke]

What was the last thing you did to the engine before this started to happen?

About 500 mile ago I reworked the heads(valves,seats,guides,etc). Rebuilt the Distributor(Mech Tach). Replaced a edlbrock carb with an original Quadrjet(Rochester).

Was cruising at about 60 went WOT and pop pop pop... Adjusted valves went away for a few miles then came back. Checked valves again no help, starting to lean toward a cam lobe going flat, or like rtj said the timing chain.

Man I really don't want to have shoe horn that big block out of that engine compartment...

 

[Bullshark]

Sorry to say, I had those exact symptoms on my 70 454 a few years back. It turned out to be a flat lobe as you fear. It was easy to see with the engine running and the valve cover off.

Bullshark

 

[big2bird]

I can tell you these original BB timing chains are crap. I have replaced two on different cars with only 50,000 miles on them.
Even if you have a bad lobe, you should still change it out to a true double roller.

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[IMG]http://i160.photobucket.com/albums/t196/big2bird/DSCN0816.jpg

 

[iburke]

Well I guess i'll put a new Short block under my rebuilt heads...

 

[DJ Dep]

I can tell you these original BB timing chains are crap. I have replaced two on different cars with only 50,000 miles on them.
Even if you have a bad lobe, you should still change it out to a true double roller.

What was it they told Dustin Hoffman?...just one word...PLASTIC. :down:

 

[Fred Mann]

Sorry to say, I had those exact symptoms on my 70 454 a few years back. It turned out to be a flat lobe as you fear. It was easy to see with the engine running and the valve cover off.

Bullshark

Once upon a time, I had a new hydraulic cam that went South in 100 miles, lifter wasn't spinning. Lots of metal missing from the lobe and the bottom of the lifter itself in a very short period of time. As Bullshark said, it is very easy to spot with the engine running and the valve covers off. Just compare the amount of movement between different valves. I wouldn't run the engine anymore until you do this check.

 

[rtj]

Man I really don't want to have shoe horn that big block out of that engine compartment...

If it's the cam, just pull the radiator, no need to pull the engine. Otherwise, a timing chain can be done with the rad in place.

Good luck.

 

[Paranoid]

Too rich, back fire through exhaust. Too lean, backfire through carb.

 

[Kid Vette]

Yep, I'm guessing wiped lobes on the cam. Had a '67 Impala way back when that had a cam go south. Same symptoms. Pull your rocker covers and start the engine and you'll know right away. :thumbsup:

 

[wburke]

oops the wife was logged in....

 

[iburke]

There works better when I logon as me.

yep ..already started pulling the valve covers...My wife says I'm not happy unless some thing is broke so I can take it apart any way. You know she may be right.:laughing:

 

[BASSIST]

There works better when I logon as me.:laughing:

Signing in as your alter ego again? :laughing: