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06-30-2011, 05:02 PM
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CC Member
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Join Date: Aug 2000
Location: Chicago,
IL
Cobra Make, Engine: ERA 454 S.O.
Posts: 1,684
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Not Ranked
Slight Miss at Part Throttle
427 S.O. Edelbrock heads and intake, MSD dist. Holley 950 HP carb. The engine idles perfect WOT is great, the plugs are a nice tan color, but at part throttle, it has a slight miss every 5 seconds or so.
It seems to be only coming from the right bank. I'm lost.
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Jeff
“If you can make black marks on a straight from the time you turn out of a corner until the braking point of the next turn, then you have enough horsepower.”
Mark Donahue
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06-30-2011, 05:10 PM
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CC Member
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Join Date: Jan 2008
Location: Williamsport,
PA
Cobra Make, Engine: Kellison Stallion 468 FE
Posts: 2,703
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Quote:
Originally Posted by Jeff Frigo
427 S.O. Edelbrock heads and intake, MSD dist. Holley 950 HP carb. The engine idles perfect WOT is great, the plugs are a nice tan color, but at part throttle, it has a slight miss every 5 seconds or so.
It seems to be only coming from the right bank. I'm lost.
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can you duplicate it when parked? look for fuel dribbles from the venturies in the carb.....
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Fred B
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06-30-2011, 05:42 PM
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CC Member
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Join Date: Apr 2009
Location: Little Rock area,
AR
Cobra Make, Engine: ERA Street Roadster #782 with 459 cu in FE KC engine, toploader, 3.31
Posts: 4,483
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Not Ranked
Are you running all mechanical advance or do you have a vacuum advance distributor? It sounds somewhat like an over-advanced condition I had with my BB Corvette motor with a vacuum advance distributor.
A bad plug wire is another possibility. Seems they show up more under light load and idle than any other time.
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06-30-2011, 06:52 PM
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CC Member
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Join Date: Aug 2000
Location: Chicago,
IL
Cobra Make, Engine: ERA 454 S.O.
Posts: 1,684
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Quote:
Originally Posted by FWB
can you duplicate it when parked? look for fuel dribbles from the venturies in the carb.....
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I would have to say, no but I will try.
__________________
Jeff
“If you can make black marks on a straight from the time you turn out of a corner until the braking point of the next turn, then you have enough horsepower.”
Mark Donahue
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06-30-2011, 06:53 PM
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CC Member
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Join Date: Aug 2000
Location: Chicago,
IL
Cobra Make, Engine: ERA 454 S.O.
Posts: 1,684
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Not Ranked
Quote:
Originally Posted by DanEC
Are you running all mechanical advance or do you have a vacuum advance distributor? It sounds somewhat like an over-advanced condition I had with my BB Corvette motor with a vacuum advance distributor.
A bad plug wire is another possibility. Seems they show up more under light load and idle than any other time.
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No vacc. advance. All of the plug wire are from 120 to 130 ohm resistance.
__________________
Jeff
“If you can make black marks on a straight from the time you turn out of a corner until the braking point of the next turn, then you have enough horsepower.”
Mark Donahue
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06-30-2011, 07:22 PM
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CC Member
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Join Date: Aug 2007
Location: Carlsbad,
Ca
Cobra Make, Engine: SPF 2932 with 438 Lykins Motorsports engine. Previous owner of FFR 5452.
Posts: 2,613
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Sounds to me like a slight lean condition. Try opening the idle air screws up a quarter turn after first adjusting them for max vacuum at idle.
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Jim
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06-30-2011, 07:26 PM
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Join Date: Dec 2001
Location: Louisville,
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Cobra Make, Engine: I'm Cobra-less!
Posts: 9,391
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At around what rpm?
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www.lykinsmotorsports.com
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07-01-2011, 04:28 PM
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Join Date: Jul 2003
Location: West Bloomfield,
MI
Cobra Make, Engine:
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Quote:
Originally Posted by FWB
can you duplicate it when parked? look for fuel dribbles from the venturies in the carb.....
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Since we're all placing bets - I go with this one. I think boosters are trying to come in. A hair larger bleed would kill signal and delay it/smooth it out.
Just guessin'... 
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Survival Motorsports
"I can do that....."
Engine Masters Challenge Entries
91 octane - single 4bbl - mufflers
2008 - 429 cid FE HR - 675HP
2007 - 429 cid FE MR - 659HP
2006 - 434 cid FE MR - 678HP
2005 - 505 cid FE MR - 752HP
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07-02-2011, 04:16 AM
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Senior Club Cobra Member
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Join Date: Dec 2001
Location: Glendale,
AZ.
Cobra Make, Engine: Cobray-C3, The 60's body lines on todays chassis technology
Posts: 2,302
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Stumble or miss only at cruise or light throttle >>
I bet this is a lean condition stumble. I would ask for all the basic/normal stuff to be checked .... float level, manifold vac. OK or no leak, timing at this RPM?, total timing.
Will it clear up if you add a bit more throttle ? It's a hot rod so add more timing and fatten her up a little more, increase RPM or get on the smooth side of the cam. Drive faster !!!
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07-02-2011, 06:22 AM
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CC Member
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Join Date: Apr 2009
Location: Little Rock area,
AR
Cobra Make, Engine: ERA Street Roadster #782 with 459 cu in FE KC engine, toploader, 3.31
Posts: 4,483
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Not Ranked
Might still be too much advance coming in at cruise. Do you have a pretty quick timing curve or a lot of total timing in the motor like 40 deg? You might experiment by pulling a couple degrees of initial timing out of it or putting in the next heavier centrifugal advance springs to slow down the curve a little. The way you describe it as - a slight miss every 5 seconds or so - sure sounds like what I experienced in my Corvette.
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09-12-2011, 02:32 PM
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CC Member
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Join Date: Aug 2000
Location: Chicago,
IL
Cobra Make, Engine: ERA 454 S.O.
Posts: 1,684
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Solved:
The idle air screw ghost must have stoped by one night. I could have sworn I checked them, more than once. I guess not. Both screws on the right were open only about 1/2 turn.  . Sett all four to a 1 1/2 turns out, runs lake a champ. Put well over 100 miles on it this weekend, never hiccuped once.
__________________
Jeff
“If you can make black marks on a straight from the time you turn out of a corner until the braking point of the next turn, then you have enough horsepower.”
Mark Donahue
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