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#1 |
Registered User
Join Date: Apr 2013
Location: Princeton, NJ
Posts: 40
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Exhaust backfire/popping
Hello guys,
I've been having this problem for a while now, and I just can't get it figured out. I have a 71 C20 with a stock 350, and it backfires or pops out of the exhaust when it hits around 2500-3000rpm. It pops erratically, anything between 1-5 seconds. It used to be worse (like popping during idle) but after changing the sparkplugs, it only does it in higher RPMs as I mentioned. It no longer backfires/pops during idle. When I let go of the gas when I shift gears, it backfires/pops/gurgles a lot too. However, once the truck has been running for several minutes and I get driving, the popping seems to be less prevalent, but still occurs on occasion. And it obviously still happens during gear shifts when I lift. I know there could be 100 reasons for why this is happening, but I'm just wondering if anyone has experienced something like this before and could give some pointers from personal experience. I think a key clue is that it only happens once the RPMs begins to pick up past 2500, and almost never happens at anything lower. Any help is appreciated, thanks! -David |
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#2 |
Registered User
Join Date: Feb 2008
Location: Fort McMurray, AB
Posts: 192
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Re: Exhaust backfire/popping
I had a similar issue a while back when I first purchased my truck, it was caused by back pressure, a bolt from the headers to the exhaust was missing, replaced the bolt and symptoms disappeared.
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#3 |
Registered User
Join Date: Jan 2010
Location: Louisa, Virginia
Posts: 30
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Re: Exhaust backfire/popping
My first thought would possibly be the points having a weak spring? Unless you've done an HEI swap.
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#4 |
Registered User
Join Date: May 2013
Location: Central NC
Posts: 830
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Re: Exhaust backfire/popping
Thats is what mine was doing...I found a worn off cam lobe eventually.
Hope its something simpler for you. Posted via Mobile Device
__________________
1972 Cheyene C-10 "Ole Green" My Grandfathers truck (early 70's to 1983) My first vehicle (1983) Original 350 (3 rebuilds) 700R4 from Bowtie Overdrives ![]() |
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#5 |
Registered User
Join Date: May 2010
Location: Broken Arrow Okla.
Posts: 510
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Re: Exhaust backfire/popping
That's what I was thinking too.
__________________
1967 swb 454 cid 700R4 trans SOLD 2006 Chevy Trailblazer SS 2013 Camaro RS convertible the wife's Build thread http://67-72chevytrucks.com/vboard/s...d.php?t=573248 |
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#6 |
Registered User
Join Date: Sep 2012
Location: Layton, Utah
Posts: 186
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Re: Exhaust backfire/popping
I had a similiar issue with my truck and it was caused by backpressure. The donut from the exhaust manifold to my exhaust. Once i sealed that nice and tight it went away.
__________________
James B. 1967 Chevy Fleetside Shortbed 4X2 (Black & Beautiful) 1971 Chevy Fleetside Shortbed 4X4 (White & Rough) |
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#7 |
Cluster King
![]() Join Date: Nov 2012
Location: Junction City, OR
Posts: 5,263
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Re: Exhaust backfire/popping
Check your distributor cap for cracks on the inside. A crack will cause spark to jump causing a misfire.
Good Luck. |
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#8 |
Registered User
Join Date: Apr 2013
Location: Princeton, NJ
Posts: 40
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Re: Exhaust backfire/popping
I recently just changed the donut gasket around the exhaust manifold flange so it doesn't leak there anymore. But the popping is still there, although it lessened.
So I checked the exhaust for other leaks by blowing a Shopvac through the pipe, and discovered quite a few places where it's leaking. (i've bolded my questions) First, the one that concerns me the most, is a leak coming from near spark plug #6. The exhaust manifold flange bends near there, but it's not coming from the flange. Nor is it coming from the plug, since it's new and very tight. It feels like it's coming from near a bolt next to plug #6 that connects the cylinder head to the block. But I'm really not sure, because the manifold blocks my view. When the motor runs, I can feel exhaust gases pumping out of there. At idle, I can feel it pulsating at just around the idle RPM, which means it probably comes from an individual cylinder, before the manifold. Does this sound like a cracked cylinder head? Or is it something else? The second exhaust leak comes from the muffler to exhaust. The connection is held together by clamps. I've tightened the clamps down extremely tight but it still leaks like crazy. How do you get rid of those leaks where two pipes stick into each other with no gasket? And my final question- is it okay to drive the truck with these exhaust leaks? Other than the smell, will it harm the motor since it's popping/backfiring? |
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#9 |
Senior Member
![]() Join Date: Apr 2011
Location: South NJ
Posts: 1,266
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Re: Exhaust backfire/popping
It's ok to drive with exhaust leaks so long as you aren't gassing yourself in the cab. I don't have an answer to why the popping is occuring, but I can answer your question about how to get rid of leaks between stuck-together pipes - weld them together.
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#10 |
Registered User
Join Date: Apr 2013
Location: Princeton, NJ
Posts: 40
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Re: Exhaust backfire/popping
Could this be an ignition timing issue? Sometimes when I turn the key off, it would run roughly for an additional second or so. And when I step on the gas, there is a little more than half a second of lag before I get any power. This is the first carbureted vehicle I've owned, so I'm not sure if these symptoms are normal or not...
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#11 |
Registered User
![]() Join Date: Jul 2013
Location: Forestburg, Texas
Posts: 659
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Re: Exhaust backfire/popping
Little chevy heads are bad about cracking between the valves. Even the good "double humps". A crack here causes a random "spit" at idle out the exhaust.
Your problem sounds like an exhaust leak. Weld the pipes together. Clamps suck! The continued run with key OFF is most likely crappy gas. Ethanol is super bad for carbed engines. Run premium only or buy your gas from a Farm Co-op. Farm gas does not have ethanol. It is legal... at least in Texas to run on the street. Or buy fuel additive that have LEAD in it. make sure it says "Not for O2 sensors".
__________________
Mark Jesus is the Way! 2003 2500HD CCLB Duramax/Ali (Clifford) 2014 2SS/RS black on black Camaro (Betty) 2006 Pontiac SOLSTICE silver/black (Lula-Bell) 1970 C/10 Short Wide (Peggy) 1964 C/10 Short Step (Hambone) RIP Jimmy Hamilton Thank you for the trucks |
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#12 | |
Registered User
Join Date: May 2013
Location: Central NC
Posts: 830
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Re: Exhaust backfire/popping
Quote:
__________________
1972 Cheyene C-10 "Ole Green" My Grandfathers truck (early 70's to 1983) My first vehicle (1983) Original 350 (3 rebuilds) 700R4 from Bowtie Overdrives ![]() |
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