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Discussion Starter #1
396 poping in the exhaust

Finnally got the car running after cam install but when you step on it starts poping sounds like detotation, have tryed several postions advanced and retarded stills does the same thing. Also pulled the covers checked the rockers all moving equally, pulled the sparks and they are shinny with no deposits on them getting worried don't want to do damage to the motor. Any ideas would be helpful, can't figure this one out should have been a easy install has turned into a nightmare. :confused: Thanks Harley
 

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when i put my engine in, i accidentially switched two plug wires... the popping is from gas not being burned in the cylinder, so you may have one cylinder thats not firing... i know you have a cam but can you tell if its shaking more than it should, or more than you expected??
 

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Discussion Starter #3
396 poping

JJ66 said:
when i put my engine in, i accidentially switched two plug wires... the popping is from gas not being burned in the cylinder, so you may have one cylinder thats not firing... i know you have a cam but can you tell if its shaking more than it should, or more than you expected??
Checked and re-checked the wires are all were they should be, all the plugs are burning the same way. :( thanks Harley
 

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Discussion Starter #5
65 Post said:
If it's a hydraulic cam, the lifters could have too much preload. Dave
Hey Dave, tryed that even went back and adjusted rockers with engine running nice oil mess. thanks Harley.
 

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Check for air leaks in exhaust systems.. 2 ways sound occures

One the "exhaust-slugg" creates a vacum behind it and sucks fresh air in that light the fuel residue in the pipe (could occure anywhere before the muffler)

Two the exhaust pressure fore its way out in the fresch air in a supersonic speed and creates an soundvave sounding like a pop or knock..
 

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Just went through this with my brother's big block. Did the plug wire check and recheck, changed the header gaskets, different dist. parts. We did put a new dist. in it that I had on the shelf but the fix was turning in the idle mixture screws on the Holley. Likely not the right fix but leaning it out took the popping noise away. The popping noise was loud with low rpm driving and it sounded like fire crackers going off in the tail pipe intermittingly. His fuel pressure is too high(IMO) @ 8-9 psi at idle. I think he should put a regulator on it.
 

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The popping sound is unburned fuel getting past the exhaust valves and exploding in the hot exhaust pipes.

Several causes.

Exhaust valves not seating (valve adjustment too tight)
Exhaust valves leaking (do a leak down check for this)
Excess fuel mixture. (re adjust your idle mixture)
Retarded spark timing. (advance base timing)
Too much exhaust duration (wrong cam)
Late exhaust closing or cam indexing incorrect. What are your cam specs?

My first guess is based ona clue you gave on a previous post. You said it was spinning fast but not firing. I'd first do a compression check on all the cylinders to check for low pressure.

Remember: Ignition disconnected, throttle blocked open
all the plugs out. Do not crank until you get the highest reading! Only 4 puffs each cylinder and record the values.

If you have been a regular reader of my advice you should know to do a compression check before and after a cam install.
 

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Discussion Starter #9
Paul Wright said:
The popping sound is unburned fuel getting past the exhaust valves and exploding in the hot exhaust pipes.

Several causes.

Exhaust valves not seating (valve adjustment too tight)
Exhaust valves leaking (do a leak down check for this)
Excess fuel mixture. (re adjust your idle mixture)
Retarded spark timing. (advance base timing)
Too much exhaust duration (wrong cam)
Late exhaust closing or cam indexing incorrect. What are your cam specs?

My first guess is based ona clue you gave on a previous post. You said it was spinning fast but not firing. I'd first do a compression check on all the cylinders to check for low pressure.

Remember: Ignition disconnected, throttle blocked open
all the plugs out. Do not crank until you get the highest reading! Only 4 puffs each cylinder and record the values.

If you have been a regular reader of my advice you should know to do a compression check before and after a cam install.
Thanks Paul some real good advice, i can try and back off a 1/4 turn on the exhaust rockers however i adjusted with motor running, backed off until chattering then down till they stopped and then a 1/2 turn more. When you say cam indexing do you mean crank gear at 12:00 and timming at 6:00 if so that is correct with out a doubt. Also have tryed advancing and retard the timming with no change when you go to put your foot into always sounds like poping from under the car sounds like from the collectors. Plugs are always strange looking the end were you adjust the gap is always shinny the rest of the plug is real clean. car starts right up and idles ok and you can notice a difference when moving the timming, also from a dead idle can usally hit the pedal quick and no poping either exhaust or carb, but take it down the road and she'll start a poping. Help!.....Harley:confused:
 

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Discussion Starter #10
Well i'm still at it with no luck have tested for everything, i guest the only thing left is a lobe wiped out. I did pull the covers earlier to watch the rockers and all moved equally. Took the car out after numerous changes but always does the same thing, idles fine, vacuum is right were it should be does anyone have any ideas before i start tearing her apart again.

Thanks Harley:confused:
 

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Did you try leaning out the mixture yet? With the engine off, turn the screws in until they stop while counting the turns. This is your reference to go back to the mixture you had. Bring the mixture screws back out to the starting point and start leaning out the mixture(clockwise). If that's not it then go back to the original settings. Are you using the vacuum advance on the dist.?
Can you tell whether it's one side or both sides of the engine that is doing this. Muffle the exhaust slightly at the rear may help identify that .
 

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Check your wires use a multi meter on the ohms scale. I had the same problem with a set of home made wires on a small block car that I owned. I changed the wires and it went away. Idled fine but under load it would pop the same way.

Jason
 

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Discussion Starter #13
Shane65 said:
Did you try leaning out the mixture yet? With the engine off, turn the screws in until they stop while counting the turns. This is your reference to go back to the mixture you had. Bring the mixture screws back out to the starting point and start leaning out the mixture(clockwise). If that's not it then go back to the original settings. Are you using the vacuum advance on the dist.?
Can you tell whether it's one side or both sides of the engine that is doing this. Muffle the exhaust slightly at the rear may help identify that .
Yes i did try leaning the mixture, you stated the vacuum advance on the dist. do you mean for the vacuum gauge? Really stumped on this one the other strange thing is the way the plugs look super clean and were you adjust the gap real shinny almost cooper like.
Harley:confused:
 

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Discussion Starter #15
Shane65 said:
There should be a vacuum hose from the dist. to the full vacuum of the intake(some cars have the hose going to the bottom of the carb).
Yes the vacuum hose from the dist. goes to the carb, has always been there prior to the cam install and ran fine before. Harley
 

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could the advance mechanism in the dist be gummed up preventing it from properly advancing as rpm's increase, causing the popping ???

my 66 Bel-Air had that problem... swapped dists and problem gone... pull cap and twist advance mechanism, it should move freely and return freely...

hope i helped.
 

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Harleynovaman: I merged your threads together so we can follow what's already been done. It's hard to remember this stuff when we have so many people.
 

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Discussion Starter #19
the Flyer said:
could the advance mechanism in the dist be gummed up preventing it from properly advancing as rpm's increase, causing the popping ???

my 66 Bel-Air had that problem... swapped dists and problem gone... pull cap and twist advance mechanism, it should move freely and return freely...

hope i helped.
I have not tryed swaping out dist. i do have a extra one worth a shot. also called a buddy to look at, will let everyone know the out come.Sure do appreciate all the help. :( Harley
 

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Sounds like your lean, according to your plug reading. Try looking for a vaccuume leak.

Does the poping stumble the car, or does it have good power through out the RPM range?

Speed
 
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