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440 backfires #2973729
10/12/21 09:59 PM
10/12/21 09:59 PM
Joined: Feb 2005
Posts: 536
Buckle of corn belt ,c. lll.
420SIX Offline OP
mopar
420SIX  Offline OP
mopar

Joined: Feb 2005
Posts: 536
Buckle of corn belt ,c. lll.
Original 440 w/70 k on it. Seems to be one cylinder backfires through the carb and exhaust. Does so intermittently. Compression 120 in all cylinders. Thinking valves are hanging up ? Worn guides ?

Re: 440 backfires [Re: 420SIX] #2973753
10/12/21 11:26 PM
10/12/21 11:26 PM
Joined: Oct 2006
Posts: 1,077
New York, USA
Chargerfan68 Offline
super stock
Chargerfan68  Offline
super stock

Joined: Oct 2006
Posts: 1,077
New York, USA
I’ve had backfire on exh side only….turned out to be broken valve spring. But, you have both int and ex backfiring.


1.50 60Ft. , 10.75@ 127MPH Hauling 3900 LBS.
Re: 440 backfires [Re: 420SIX] #2973773
10/13/21 02:08 AM
10/13/21 02:08 AM
Joined: Jan 2003
Posts: 1,823
s. e. pa.
C
calrobb2000 Offline
top fuel
calrobb2000  Offline
top fuel
C

Joined: Jan 2003
Posts: 1,823
s. e. pa.


get some trans fluid and pour it in carb with engine running till it smokes real good then por fast enough to stall it !

let sit for 30 min.

put 3 oz. in fuel tank

this will free stickey valves !

start and drive

Re: 440 backfires [Re: calrobb2000] #2973809
10/13/21 08:44 AM
10/13/21 08:44 AM
Joined: Feb 2005
Posts: 536
Buckle of corn belt ,c. lll.
420SIX Offline OP
mopar
420SIX  Offline OP
mopar

Joined: Feb 2005
Posts: 536
Buckle of corn belt ,c. lll.

Worth a try..Easier than pulling the heads

Re: 440 backfires [Re: 420SIX] #2973810
10/13/21 08:47 AM
10/13/21 08:47 AM
Joined: Aug 2005
Posts: 1,273
Az
69hemibeep Online content
pro stock
69hemibeep  Online Content
pro stock

Joined: Aug 2005
Posts: 1,273
Az
Friend just went through this and found a bad plug wire!


1969 Hemi Roadrunner 2nd owner
Re: 440 backfires [Re: 420SIX] #2973819
10/13/21 09:27 AM
10/13/21 09:27 AM
Joined: Nov 2015
Posts: 565
Missouri
J
jwb123 Offline
mopar
jwb123  Offline
mopar
J

Joined: Nov 2015
Posts: 565
Missouri
Put a vacuum gauge on it. low steady vacuum is a problem, or something that affects all the cylinders, worn timing chain, lean fuel etc. . If the needle bounces it is a valvetrain issue, broken valve spring flat cam etc. If it has normal vacuum then it may be electrical.

https://m.roadkillcustoms.com/diagnose-common-engine-problems-vacuum-gauge/#:~:text=Vacuum%20Gauge%20Engine%20Condition%20Indicators%20%20%20,Confirms%20worn%20rings.%20%2012%20more%20rows%20

Re: 440 backfires [Re: jwb123] #2973829
10/13/21 10:26 AM
10/13/21 10:26 AM
Joined: Jan 2003
Posts: 16,929
So Near, Yet So Far
topside Offline
I Live Here
topside  Offline
I Live Here

Joined: Jan 2003
Posts: 16,929
So Near, Yet So Far
Has anyone worked on it recently ?
Had something like that when 2 wires were crossed (to wrong spark plugs) on right bank.
Think it was #4 and #6.
Verify dist cap & rotor are healthy & clean (carbon tracking).

Re: 440 backfires [Re: topside] #2973887
10/13/21 11:45 AM
10/13/21 11:45 AM
Joined: Jan 2003
Posts: 5,437
Hot Rod Ridge
FastmOp Offline
master
FastmOp  Offline
master

Joined: Jan 2003
Posts: 5,437
Hot Rod Ridge
Counterclockwise

Re: 440 backfires [Re: FastmOp] #2973888
10/13/21 11:56 AM
10/13/21 11:56 AM
Joined: Sep 2007
Posts: 783
West Virginia
B
B1Frank Offline
super stock
B1Frank  Offline
super stock
B

Joined: Sep 2007
Posts: 783
West Virginia
I had one 440 do that....turned out to be a cam with a bad lobe, ...that was it.

Re: 440 backfires [Re: FastmOp] #2973889
10/13/21 12:00 PM
10/13/21 12:00 PM
Joined: Jan 2003
Posts: 5,859
Anoka County, MN
L
Leigh Offline
master
Leigh  Offline
master
L

Joined: Jan 2003
Posts: 5,859
Anoka County, MN
Probably been checked, but make sure one advance weight isn’t stuck. Will backfire on decel.

Re: 440 backfires [Re: Leigh] #2974109
10/13/21 08:33 PM
10/13/21 08:33 PM
Joined: Dec 2012
Posts: 206
Alberta
4
440_Offroader Offline
enthusiast
440_Offroader  Offline
enthusiast
4

Joined: Dec 2012
Posts: 206
Alberta
Fouled spark plug?







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