Popping sound in exhaust

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dart_68

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Got a question I hope to get some direction. I've got a 360 in a Duster that has popping sounds in the exhaust. I'm sure it's not an exhaust leak; not a ticking sound. It has a deeper tone and sounds a lot like the lean out pop you might get when you suddenly close the throttle but not as loud. This is occurring at idle and also coincides with a stumble that varies in intensity. The pops are not even, sometimes happening in pairs, etc.

Let me know if you need more specific info on the engine.

Thanks.
 
Could be many things, pop out the exhaust is usually to rich not lean, fouled plug, bad wire, fuel building up in the exhaust then igniting. Then it could be a mechanical problem, burnt valve, cam lobe, and so on.
Check the easy stuff first.
 
Could be many things, pop out the exhaust is usually to rich not lean, fouled plug, bad wire, fuel building up in the exhaust then igniting. Then it could be a mechanical problem, burnt valve, cam lobe, and so on.
Check the easy stuff first.
Head are fresh. I'll pull the plugs tonight and see what they can tell me.
 
I pop out the exhaust a lot, but I think that's different than what you're talkin about.
 
Pop out exhaust =open/non seated valve.
Raw gas making it into exhaust primary tract because it's not fully burning... then it lights off... pop ..... pop......pop...
Would be igniting in the exhaust even though the headers are cool? Is that possible?
 
Update:

Pulled the plugs and they all show very rich even to the point that the plugs are still wet. Smell very much of gas. The plugs were new and even though I've run this engine for maybe a total of 3 minutes they still were carbon black but at least all even so all were firing...mostly...just saying..
 
Update:

Pulled the plugs and they all show very rich even to the point that the plugs are still wet. Smell very much of gas. The plugs were new and even though I've run this engine for maybe a total of 3 minutes they still were carbon black but at least all even so all were firing...mostly...just saying..


What carb are you using?
 
What carb are you using?
It's a Holley 750 vacuum secondary with manual choke. I bought this used and the weird thing is it has a secondary metering block instead of a metering plate like every other Holley vacuum secondary I've ever seen. I did check the floats and their right on. I did go through this carb before installing it.
 
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Update:

I finally got the engine running well enough that it will idle and was able to get a short video. You can hear the "popping" I'm talking about. Any ideas what the problem may be?
 
Update:

I finally got the engine running well enough that it will idle and was able to get a short video. You can hear the "popping" I'm talking about. Any ideas what the problem may be?


Valve train !!
 
I would call that 'banging' not 'popping' LOL. Not like any exhaust leak I've experienced.

After listening a couple of times, I'm on the same track as FB and others: I'd be wondering if the valves were hanging open a bit. Poor valve work or maybe too long pushrods?

Another thought is crossfiring in the ignition... like in the rotor alignment being off, or weak ignition causing cylinders to not fire at times and them dump unburned fuel into the exhaust.
 
It's a Holley 750 vacuum secondary with manual choke. I bought this used and the weird thing is it has a secondary metering block instead of a metering plate like every other Holley vacuum secondary I've ever seen. I did check the floats and their right on. I did go through this carb before installing it.
A long time ago, Holley used to put the block on the secondary side too. Or somebody retrofitted it... there are kits to add it.
 
More specifics on engine. Double check your firing order. Number one is drivers front, number 2 passenger front. If that is correct I would pull the valve covers and look for broken things put a straight edge across the valve tips. See if one is shorter. That sounds like the cylinder is firing on the up compression stroke or a sticking valve.
 
Did the machine shop that did the heads grind the valve tips to set the correct length measured from the valve spring seat to the valve tip?

The first 440 I rebuilt when I was a kid popped at idle. What I found was that when the lifters pumped up it held some of the exhaust valves open enough that when it fired it would pop. It turned out the machine shop didn't check the exposed length of the valve and essentially some were long and had to be ground. There is a spec for the length range.
 
Thanks for the replies! It definitely sounds like its lighting off in the headers. You can hear in the tail pipes pretty loud. It does it right from the get go after starting before the headers have time to heat up. I've checked the ignition including firing order. Not sure about the rotor phasing yet but I'm thinking the problem is the exhaust valves hanging. I bought the motor complete but apart. The heads had been done by a machine shop and were still wrapped in plastic. Don't know what shop, though. What is the correct length pushrods for a stock 1990 360?
 
I found out with mind that the vacuum advance was shot on my distributor. And was popping thru the exhaust. Motor was shaking at idle so I pulled hose off distributor and the shake went away..my 002
 
I found out with mind that the vacuum advance was shot on my distributor. And was popping thru the exhaust. Motor was shaking at idle so I pulled hose off distributor and the shake went away..my 002
Easy enough. I'll try that tonight when I get home. Thanks.
 
I found out with mind that the vacuum advance was shot on my distributor. And was popping thru the exhaust. Motor was shaking at idle so I pulled hose off distributor and the shake went away..my 002
That was it! Pulled the vacuum hose and plugged the port on the carb and it runs great and NO popping. Never would have thought of that.
:thumbsup:
 
I found out with mind that the vacuum advance was shot on my distributor. And was popping thru the exhaust. Motor was shaking at idle so I pulled hose off distributor and the shake went away..my 002
What did you finally do to rectify the situation? Did you get a new vacuum advance canister?
 
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