Running Rough after 20 Minutes
#56896
04/20/08 01:49 PM
04/20/08 01:49 PM
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Joined: Aug 2004
Posts: 1,213 Los Angeles, CA
Mobarge
OP
pro stock
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OP
pro stock
Joined: Aug 2004
Posts: 1,213
Los Angeles, CA
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My Plymouth runs great right after I start her up, but after about 20 minutes of freeway or surface street driving (after heating up to normal operating temp), she starts running rough: The idle drops, and when I take off from a stop light under normal load, she backfires a few times through the exhaust.
I'm running a 413, MSD-6AL, MSD wires (new), Speed Demon 750, recurved FBO distro, new FBO coil, Accel header plugs (I've been running them about a year now - 500 miles), and 101 octane pump gas (real pump gas, not octane boost). Timing is set to 38* (per the distro spec sheet).
Any thoughts?
'71 SSP - SOLD!
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Re: Running Rough after 20 Minutes
[Re: Mobarge]
#56897
04/20/08 02:14 PM
04/20/08 02:14 PM
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Joined: Jan 2003
Posts: 5,890 Athens, Greece
Pyper70
master
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master
Joined: Jan 2003
Posts: 5,890
Athens, Greece
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is your fuel line a little too close to your exhaust or trapped against the block some place where there isn't circulation. Maybe you aren't getting enough fuel to your bowls due to vapor lock. Do you run steel braid/hose or brake/fuel line pipes?
Family owned 1969 Charger R/T DualQuad 440/727/GVO/3.55s
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Re: Running Rough after 20 Minutes
[Re: Pyper70]
#56898
06/28/08 06:57 PM
06/28/08 06:57 PM
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Joined: Aug 2004
Posts: 1,213 Los Angeles, CA
Mobarge
OP
pro stock
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OP
pro stock
Joined: Aug 2004
Posts: 1,213
Los Angeles, CA
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Sorry to resurrect a two month old thread... but the problem is still there. I put in a phenolic gasket / billet spacer from Don at 4 Seconds Flat yesterday (in case I was boiling the fuel), and it still seems to have this backfire problem that seems to be tied to heat (by the way, for those who don't have the 4 hole spacer on a dual plane... get one. The throttle response is great!).
To answer the above poster, I am running 3/8 aluminum tubing all the way from the tank in the stock location. eight inch section of 3/8 rubber fuel line to the fuel pump (Carter mechanical, 120 GPM @ 6 - 8 PSI), three inch section 3/8 rubber from fuel pump to Edelbrock billet fuel filter, short 3/8 rubber connector to 3/8 aluminum tubing running up to the carb in the stock location (behind the alternator, underneath distro and over intake manifold). It's not running near the headers at all, and is about a 1/2 inch away from the block at the closest (below the distro). Other than that, fuel line is away from the block.
Would a braided line cut down on the heat soak (if there is any)? Also, I have a new (stock) vapor separator. Should I throw this in, and set a return line to the tank? Would this help at all (no return line now).
This problem has had me scratching my head for a long time now. Any help would be appreciated.
'71 SSP - SOLD!
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Re: Running Rough after 20 Minutes
[Re: racincuda]
#56900
06/28/08 09:18 PM
06/28/08 09:18 PM
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Joined: Aug 2004
Posts: 1,213 Los Angeles, CA
Mobarge
OP
pro stock
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OP
pro stock
Joined: Aug 2004
Posts: 1,213
Los Angeles, CA
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Rockers are non-adjustable. Engine has about 500 - 750 miles on it, tops.
'71 SSP - SOLD!
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Re: Running Rough after 20 Minutes
[Re: Mobarge]
#56901
06/29/08 12:19 AM
06/29/08 12:19 AM
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Joined: Nov 2006
Posts: 1,074 Manitoba Canada
67autocross
super stock
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super stock
Joined: Nov 2006
Posts: 1,074
Manitoba Canada
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This is the same thing my 83 chev short box truck is doing, it's driving me off the deep end trying to fix it.
A new iron curtain drawn across the 49th parallel
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Re: Running Rough after 20 Minutes
[Re: polkat]
#56906
06/29/08 01:29 PM
06/29/08 01:29 PM
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Joined: Aug 2004
Posts: 1,213 Los Angeles, CA
Mobarge
OP
pro stock
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OP
pro stock
Joined: Aug 2004
Posts: 1,213
Los Angeles, CA
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Thanks for the tip on the plugs. I was actually thinking I should switch to a hotter plug. Any recommendations on which part number NGK I should start with? No choke on the carb, so it can't be that.
'71 SSP - SOLD!
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