help annoying pop in exhaust

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mstory

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I have a rebuilt .040 360 stock rotating assembly 1.88 j heads milled .015 valve job new seats comp springs lifters timing chain comp thump .486 edelbrock intake holley 600 compression test on all cylinders around 120 I have true duals and the pop comes from drivers side at idle consistent pop pop pop and that side of the exhaust is warmer than the pass side the pop is loud enough to drown the hooked aero chambers I'm lost adjusted carb timing all rockers seem to work also I changed to height distributor
 
My first thought was a exhaust leak also...

But, I'd like to know how the valve adjustment was arrived at...meaning preload? I may be off base here, but with the slight head mill, new head gaskets (thickness) and new cam, did you measure for the proper pushrod length for this application or just use the stock one's and hope for the best.

Regardless, you may still be in spec, but I'm just curious?
 
When u put the motor back together did u have ur timing set at zero advance or retard? I know with the comp thumprs that they are already adjusted to a 102 lsa so there is no need to adjust it any more than factory dot to dot line up on ur timing gears... That pop could be to much advance or retarded timing which would lead to a almost misfiring sound
 
It does have a header leak but that's not the pop I'm hearing.

When I installed cam I didn't advance any just lined up the dots

Factory pushrods were reused I can roll motor and spin all push rods with my fingers I haven't checked rocker arms with a feeler Gauge but I don't think they are to tight

The sound is more noticeable from the rear and only from driver side exhaust passenger sounds normal
 
Even with open headers the sound was noticeable but this being my first build I figured header noise and a muffler and exhaust would fix it after the rest got quit the popping became more noticable
 
A leak at the header flange or a cracked pipe up near the head,will let fresh air into the header and cause any unburned fuel there to continue burniing. The expanding gases will hurry through the primary pipe and and pop when they hit the collector.
A problem with an exhaust valve can do that too.If its not sealing then during the intake stroke the piston will draw exhaust into the chamber along with a partial charge from the carb. This then is a hot, and probably lean mixture. then on the compression stroke, some of that charge may escape into the primary pipe, where it may ignite and burn, leading to a pop.As the rpm goes up there is less and less time for these things to happen, and the popping quits.
A compression test or a leakdown test,on a cold engine may not catch this. I would do a leakdown test on a fully warmed up engine.
Late ignition timing can do it too.If the fire isnt started early enough, the fuel charge may not have all finished burning when the exhaust valve opens.In this case though most all the cylinders will be popping.
An incorrectly set mixture screw, or a faulty low speed circuit could lead to misfires where the mixture could also ignite in the primary, but it would require oxygen to be there and that takes us back to the leaking header flange.
Before I would do anything I would drop that header and inspect the gasket. I dont suppose you are using one of those emission heads with the AIR ports, and the header gasket doesnt cover it?That would be an oops moment.
 
Are you sure the pop is going out the exhaust or could it be popping back up through the carburetor?
 
Broken insulator on a spark plug maybe? Could be erratically firing and causing the pop! Had it happen before, drove me nuts cause the plugs were "new"!! Geof
 
I have changed one plug and swapped one wire cause initially #7 cylinder had low compression compared to rest after another test today all cylinders around 120 with pop still there I guess I should start maybe with plugs and wires on that side? Also lookin at ordering aluminum header gasket to fix the leak possibly the cause
 
Hipo65 said:
Heck to see if #5 & #7 didn't get swaped around. I've done it its easy to do man.
Click to expand...

I agree. Double and triple check the plug wires. I once swapped #4 and #6 on an engine that was pretty newly rebuilt. I had a weird slight miss. I was about to pull the heads when my co-worker told me to double-check the firing order. I had 4 and 6 swapped. Switched them back and the miss was gone!
 
Ok so I started pulling plug wires and when I pull #1 pop stops new plug still pops
 
Took a double check on wires they are correct also I swapped the #1 wire to a wire on the other side of engine to test wire same pop drivers side
 
I would loosen all the intake bolts and retorque them ,I've had this type of problem before.
 
Well since youve been able to isolate the cylinder, Ive got a test for you that can prove the exhaust valve is or isnt hanging up.
It goes like this; Get the engine running on the passenger side cylinders and #1 only. Then put a section of cerealbox ,or similar stiff but a tad flexible material,against the driver side collector. If that posterboard gets sucked up against the flange after every pressure pulse that would be the piston sucking it there through an open exhaust valve. Bad news.
I have never done this on a V8.You may be the first guy on the planet to try. It works really well on small engines, with instant verification..
To disable numbers 3,5, and 7 which all dump into a common collector, I think the best way would be to remove the spark plugs, and to short the plugwires to ground.Otherwise the header-pulse tuning will give an erroneous reading.Yeah it will be noisy. The curb idle screw will need to be cranked in to keep the engine running. Dont forget to back it out later.
I guess it would be wise to have a fire extinguisher handy. There may be some fuel being expelled from the open cylinders.Ive run one open like that now and then, but never three.The one open didnt expel fuel at idle.
Or you could just drop the header and check the clamp-pattern.I think I said that one time already.
Ok so good luck.
 
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