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Author
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Topic: Stumbling after shut off....
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'69PonyRider
Gearhead Posts: 238
From: Hawthorne, CA
Registered: Sep 2001
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posted 06-14-2004 11:38 PM
   
When the engine gets warm and i shut it off, it kinda stumbles like it wants to keep going. Im running around 10.5 comp, forged pistons, 305H cam. I used 91 with 1 bottle of NOS octane booster with nitro. it still stumbled so i added one more bottle. and it still stumbles but a little less. timing is at 20*. Could this be detonation? it doesnt do it when its cold. the rpms go up a bit too at idle when warm. what can cause this?Aldo
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67nightmare
Gearhead Posts: 118
From: rose hill, ks, usa
Registered: Mar 2004
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posted 06-14-2004 11:51 PM
Its sounds like a timing problem especially considering how much octane booster you are using. I can't suggest a certain number for timing or anything but it sounds a little to far advanced to me.
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'69PonyRider
Gearhead Posts: 238
From: Hawthorne, CA
Registered: Sep 2001
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posted 06-15-2004 01:51 AM
It used to be at 14 but I advanced it. it feels better at 20. even at 14 it stumbled. but could it be that my cam is too advanced? i lined up the dots but you never know.Aldo
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Fastymz
Moderator Posts: 20638
From: Reno Nv USA M&M#1240
Registered: Apr 2001
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posted 06-15-2004 02:17 AM
Whats you total advance and it's all in by when ?------------------
SCOOP oddly obsessed with big scoops on little Mustangs 65 coupe,351w,C4,Big Boss 429 hood scoop,8" 3.40 TracLoc. My Pics
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Buster
Gearhead Posts: 1553
From: Hurricane alley
Registered: May 2002
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posted 06-15-2004 06:17 AM
It's either idling too fast or it's too rich....
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indyphil
Gearhead Posts: 2690
From: Senoia, G.A. USA
Registered: Jul 2002
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posted 06-15-2004 10:24 AM
When you shut it off there should be no more spark, so timing should not be an issue.
It runs on because there is enough residual heat in there to ignite the fuel - like a diesel engine it just ingites from the heat of compression. Sometimes this happens when there are heavy deposits in the engine or when the spark plug gets really hot. Buster is right - too rich of a mixture will also cause this (the extra richness often also contributes to the burnt deposits)Anyway lots of things to look for.
Make sure your running at the correct temp, correct mixture etc... Do a plug read and make sure the plugs are in good shape (check gap, and check that electrodes are not worn away - when they get thin they also get too hot and can create a little glowing red heat source even when theres no spark) ------------------
'68 coupe, '66 289 C code
engine, edel 600cfm carb, performer intake, dual exhaust http://www.geocities.com/ottouk_77/68mustang.htm
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bluestreek
Gearhead Posts: 1724
From: Athens,GA
Registered: Jul 2001
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posted 06-15-2004 12:14 PM
Above info is good. What is your idle rpms? High idle speed or a vacuum leak combined with high cumbustion chamber heat can cause run-on even after the spark is shut off. Try dropping the idle speed down some if possible and if that don't do it maybe drop the timing down 2 deg. This usually helps.------------------
1966 Mustang Coupe: Custom glass hood and BIG scoop sits atop a 289 stroked to 331 c.i., Steel crank, rods and girdle, TFS alum. heads, Stealth 8020 intake, Xtreme 268 Solid Roller, Holley 750 HP, long tubes, 4speed, 9" 3.50 posi.
11.86 @ 116 mph (7.62 @ 93 mph)daily driver!
DanH
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'69PonyRider
Gearhead Posts: 238
From: Hawthorne, CA
Registered: Sep 2001
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posted 06-15-2004 02:20 PM
What type of plugs should i be running? right now i have champion platinums. the gap is stock at 34? but i have an msd 6AL setup.Ill check the idle too, its idling at around 1200 in park and 950 in gear but the rpms go up to 1200 in gear when it gets hot. vacuum is at around 7" and drops to 5* in gear i have a 4.5" power valve, 75 jets in the front 80 in the back.
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Fastymz
Moderator Posts: 20638
From: Reno Nv USA M&M#1240
Registered: Apr 2001
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posted 06-15-2004 05:42 PM
Go down on the Power Valve to a 3.5 or a 2.5 or just plug it. Also the idle seems alittle high, how does it run if you lower the RPM ?
Also do the idle screws do anything when you turn them all the way in ?
If the screws aren't working then try openning the secondarys alittle at idle,or drill two small 1/16 holes in the primary blades, then reset the idle screws and idle speed. This really help clean up my idle lots. ------------------
SCOOP oddly obsessed with big scoops on little Mustangs 65 coupe,351w,C4,Big Boss 429 hood scoop,8" 3.40 TracLoc. My Pics
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Dubz
Gearhead Posts: 1888
From: Manitoba Canada
Registered: Oct 2002
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posted 06-15-2004 06:07 PM
that would be dieseling.what engine temps are you looking at?
could be deposits in the engine
could be timing is too far advanced
could be timing is too retarded
could be too high of an idle
too lean of a mixture may cause the problem as well as too rich lots of stuff to troubleshoot. reading the plugs should tell you rich or lean, and playing with the idle isn't too hard, or adjusting timing. good luck [This message has been edited by Dubz (edited 06-15-2004).]
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