Thread: Popping sound
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06-18-2006 08:28 PM #1
Popping sound
When I drive my car (350, stock dished pistons on a stock bottom end, RPM Air-Gap intake, 750 holley, vortec heads, msd ignition, comp 268XE cam, 1/2 fuel line with a holley black fuel pump 150ish GPH) on the street, just cruising, i hear and feel a pop or backfire. Under acceleration it works fine. When we built the engine we didn't have it bored, just re-ringed and the top end is completely new except the carb. It is the second carb we put on it. We got this one from a race shop we go to and they both said it was a perfectly good carb when the gave it to use. I know a 750 is alittle big but would that make it pop? is there something that makes it pop that I'm not seeing? I don't really know what to ask, I guess just looking for some suggestions on what to check.
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06-19-2006 12:42 AM #2
timing?...just because your car is faster, doesn't mean i cant outdrive you... give me a curvy mountain road and i'll beat you any day
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06-19-2006 01:24 AM #3
what kind of heads?If I knew anything I'd be dangerous.
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06-23-2006 10:45 PM #4
Originally Posted by TUBJUB
I HAD THE SAME PROBLEM AND WHAT HAPPENED TO ME WAS MY CAM LOBES WORE AND CAUSING THE VALVES NOT TO OPEN AND CLOSE PROPERLY...ALSO MAKE SURE YOU GOT THE VALVES ALL ADJUSTED PROPERLY!!!!HOPE THIS HELPS OUT!Donny Wagers
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06-23-2006 10:52 PM #5
we ckecked the timing and its was fine. 13 initial and 36 total.
heads are vortec off a pickup
we can check the cam but its not consistant enough to be that. it only happens when im cruising, not under acceleration.
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06-23-2006 11:50 PM #6
Originally Posted by TUBJUB
ALSO WHAT KINDA CAM YOU RUNNING? IS THE CAM NEW OR USED,,,,,IF THE CAM IS OLD,YOU BETTER CHANGE IT..
STOCK OR? ,?
YOU ALSO COULD HAVE A (BENT VALVE)
I HAve WORKED ON MANY CHEVY SMALL BLOCKS.
gotta be in the valve train (for sure)Last edited by DONNY43; 06-23-2006 at 11:54 PM.
Donny Wagers
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06-23-2006 11:48 PM #7
Originally Posted by DONNY43
SO TELL ME ,,IS THE MOTOR FRESH? OR DO YOU GOT MANY MILES ON HER?
THANKS..Donny Wagers
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06-24-2006 12:04 AM #8
Popping at cruise but not at full power tells me it's not mechanical. It's a carb or ignition issue. Is it popping through the carb or through the exhaust?
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06-24-2006 12:23 AM #9
yup.... valve train is generally gonna affect more at idle and acceleration.... :edit: while i was on the "throne of thinking" i thought maybe you should see if your either advancing too early of an RPM when just cruising not puttin a ton of gas in it, or maybe you're advancing too late of an RPM and not getting enough timing at your cruise RPMLast edited by thesals; 06-24-2006 at 12:30 AM.
just because your car is faster, doesn't mean i cant outdrive you... give me a curvy mountain road and i'll beat you any day
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06-24-2006 08:10 AM #10
Originally Posted by thesals
JUST A THOUGHT.GOOD LUCK!Donny Wagers
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06-24-2006 09:42 AM #11
the engine has about 5000 miles, all be it a few hard miles at the track.
the cam is a new comp cams xtreme energy 268. lift 477in/480exh with probably only 1000 miles, if that, on it and the springs to match and the heads were worked at accept a bigger lift.
i believe the popping is from the exhaust, i can feel it in my feet. but it is kinda hard to see the carb while driving. and when my dad was following my once (incase i broke down) he could hear it and it puffed out smoke everytime it popped.
i'll try the slow reving in park and see what happens.
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06-24-2006 11:42 AM #12
Originally Posted by TUBJUB
so ur saying the popping is from the exhause not the carb,,,,please try this in park,,,and let me no what happens,,also im thinking you may have some adjustment issues on the valves
(exhaust valves,,,,,)im wondering how did u adjust them ,,Last edited by DONNY43; 06-24-2006 at 11:44 AM.
Donny Wagers
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12-06-2006 09:29 PM #13
was this ever resolved, I have read in other forums about comp cams core quality and how it relates to excellerated lobe wear. Any new updates to this problem, To me it sounds like a timing and carb issue, good place to start and check before ripping the motor apart. Another trick for testing the cam is mark a black line on the pushrod tops below the rocker, fire the motor up and have someone verify that the pushrods are turning, most cases if the lobe is gone the pushrod will not rotate.old habits die hard
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12-06-2006 10:21 PM #14
we gave up. the cam hole was about 1/2 inch off center of the crank hole in the block. the carb was also bad and had shavings of the rod bearings running through the engine, not so good.
So sad, sorry to hear it.
We Lost a Good One