Run On
Thread Starter
Instructor
Joined: Aug 2007
Posts: 131
Likes: 0
From: Madison NJ
Run On
Brand New crate 383 just installed and it runs great. Starts right up, no pinging, no problems when hot, running 93 pump gas but when I go to shut it off I get a second or two of run on.
What causes this and how do I fix it.
What causes this and how do I fix it.
Tech Contributor
Joined: Jun 2004
Posts: 20,905
Likes: 962
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Most of the time it's because of insufficient advance timing at idle speed, and the resulting band-aid of large throttle opening. I would check these two items.
Drifting
Joined: Apr 2002
Posts: 1,720
Likes: 19
From: Manhattan Beach Ca
I would say sometimes there is nothing you can do about it and you have to live with it.
I've gone through a couple engines and they both did it off and on even with brand new engine. Look and see if it actually spins backwards. My theory is it's mainly leftover carbon or fuel vapor after a very hot shut down. I did notice when I removed my PCV system that it seemed to go away almost for good.
I've gone through a couple engines and they both did it off and on even with brand new engine. Look and see if it actually spins backwards. My theory is it's mainly leftover carbon or fuel vapor after a very hot shut down. I did notice when I removed my PCV system that it seemed to go away almost for good.
Drifting
Joined: Aug 2005
Posts: 1,682
Likes: 3
From: League City TX
Adjust the idle screw to close the throttle blades a little, and then add timing to compensate for the lower idle speed.
If you arent currently running vacuum advance connected to a manifold vacuum source, doing so would likely accomplish what you need.
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
Most probable cause of this is ported vacuum to the distributor - instead hook it to full time manifold vacuum. As soon as you do this, you'll notice the engine idle speed increased because it's running more efficiently (faster), so you'll have to reduce the idle speed with the idle speed screw. Now the engine will cut off smartly when you kill the ignition.
Thread Starter
Instructor
Joined: Aug 2007
Posts: 131
Likes: 0
From: Madison NJ
Most probable cause of this is ported vacuum to the distributor - instead hook it to full time manifold vacuum. As soon as you do this, you'll notice the engine idle speed increased because it's running more efficiently (faster), so you'll have to reduce the idle speed with the idle speed screw. Now the engine will cut off smartly when you kill the ignition.
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Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
Your builder needs better education. Read the stickies on timing:
http://forums.corvetteforum.com/c3-t...long-post.html
Unmodify your distributor or get one that has a working vacuum advance.
http://forums.corvetteforum.com/c3-t...long-post.html
Unmodify your distributor or get one that has a working vacuum advance.
Tech Contributor
Joined: Jun 2004
Posts: 20,905
Likes: 962
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
No problem. Just add an additional couple of degrees to your initial timing, and hook up the vacuum advance. Take it out for a run and let us know how the engine reacts to the changes.
Race Director
Joined: Apr 2000
Posts: 17,676
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Yeah I agree advance the timing and lower your idle speed at the carb with idle speed screw. I don't even want to get into a vacuum advance debate 
Thread Starter
Instructor
Joined: Aug 2007
Posts: 131
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From: Madison NJ
Tech Contributor
Joined: Aug 1999
Posts: 14,380
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From: At my Bar drinking and wrenching in Lafayette Colorado
Engine run-on is caused by excessive idle speed and/or excessive throttle blade opening at idle.
For factual info on timing and vacuum advance, just drop me an e-mail request for my papers on timing and vacuum advance. There's no reason for you not to run vacuum advance if you are running on the street with more than 9 inches of manifold vacuum.
For factual info on timing and vacuum advance, just drop me an e-mail request for my papers on timing and vacuum advance. There's no reason for you not to run vacuum advance if you are running on the street with more than 9 inches of manifold vacuum.
Race Director
Joined: Apr 2000
Posts: 17,676
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
I am in the no vacuum advance club, on a stock or near stock motor then yes I'm all for it but once you start to push the limits with pump gas and compression ratio and timing you can get into some detonation problems if you have the added vacuum advance which in some cases can advance you timing to over 52 degs.
Drifting
Joined: Apr 2006
Posts: 1,911
Likes: 2
From: gold coast queensland
i agree with 69427 . im assuming your timing was set on around 12 initial with a crate 383 . you may need anywhere from 14-20 initial and then loc out your distributor to suit . 32 total seems a little low to me. fast burn heads work well with 34 but most other 350-383,s 36 is good.
you really need to sort it out as its damaging to your motor. just until you get it sorted leave your car in drive when you turn it off and it shouldnt run on. its a catch 22 cause thats not the best for your transmission but its better then run on in a motor.
i didnt hear what carb you are running but if its a demon then the transission slots absolutely have to be set to .020 showing.
i know your the man on here lars to most but why when you said this "Engine run-on is caused by excessive idle speed and/or excessive throttle blade opening at idle" did you not include low initial timing as a possibility because someone can have correct idle speed and correct throttle blade opening and still get run on.
you really need to sort it out as its damaging to your motor. just until you get it sorted leave your car in drive when you turn it off and it shouldnt run on. its a catch 22 cause thats not the best for your transmission but its better then run on in a motor.
i didnt hear what carb you are running but if its a demon then the transission slots absolutely have to be set to .020 showing.
i know your the man on here lars to most but why when you said this "Engine run-on is caused by excessive idle speed and/or excessive throttle blade opening at idle" did you not include low initial timing as a possibility because someone can have correct idle speed and correct throttle blade opening and still get run on.
Last edited by gingerbreadman1977; Jan 25, 2010 at 02:39 AM.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,390
From: At my Bar drinking and wrenching in Lafayette Colorado
i know your the man on here lars to most but why when you said this "Engine run-on is caused by excessive idle speed and/or excessive throttle blade opening at idle" did you not include low initial timing as a possibility because someone can have correct idle speed and correct throttle blade opening and still get run on.
Lars
Last edited by lars; Jan 25, 2010 at 09:02 AM.
Thread Starter
Instructor
Joined: Aug 2007
Posts: 131
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From: Madison NJ
The engine builder told me the timing at idle (850 to 900 RPM) is set at 10 degrees.
He said do not hook up the vacuum advance and that he welded a bead on my distributor so it would be 32 degrees at total advance.
Engine Model - 383ci
Horsepower - 420 HP
Torque - 460 Ft Lbs
Bore and Stroke - 4.030 x 3.750 Inches
Compression Ratio - 10:3
Camshaft - Hydraulic roller 224/230 535/544
Lifters - OEM style hydraulic roller
Heads - 200cc Dart Iron Eagle, 72cc chamber
Valves - Stainless steel 2.02 Intake 1.60 Exhaust
Rocker Arms - Aluminum full roller, 1.6 ratio
Ignition Timing - 32 degrees at 4,000 RPM
Vacuum at idle 10 inches
The engine builder is T&L Engines and they will not respond to any emails or phone calls I send to them.
Were do I start. Do I hook up the vacuum advance? How will the affect the bead welded for 32 degrees of total advance that the builder recommends. Is 10 degrees at idle too low? I AM SO CONFUSED!
He said do not hook up the vacuum advance and that he welded a bead on my distributor so it would be 32 degrees at total advance.
Engine Model - 383ci
Horsepower - 420 HP
Torque - 460 Ft Lbs
Bore and Stroke - 4.030 x 3.750 Inches
Compression Ratio - 10:3
Camshaft - Hydraulic roller 224/230 535/544
Lifters - OEM style hydraulic roller
Heads - 200cc Dart Iron Eagle, 72cc chamber
Valves - Stainless steel 2.02 Intake 1.60 Exhaust
Rocker Arms - Aluminum full roller, 1.6 ratio
Ignition Timing - 32 degrees at 4,000 RPM
Vacuum at idle 10 inches
The engine builder is T&L Engines and they will not respond to any emails or phone calls I send to them.
Were do I start. Do I hook up the vacuum advance? How will the affect the bead welded for 32 degrees of total advance that the builder recommends. Is 10 degrees at idle too low? I AM SO CONFUSED!
Drifting
Joined: Aug 2005
Posts: 1,682
Likes: 3
From: League City TX
Your engine would probably run best with 2-4 degrees more total timing than the 32 degrees that you are running right now.
If you bump your timing up 2° and then readjust your idle, that may solve the problem.
You will want to make sure to listen closely for any pinging that may occur under load, but 34° should be pretty safe.
If that doesnt work, try another 2° and listen closely again.
Telling you to run your engine at 32° total, and not to use any vac advance sounds like the builder wants a very safe tune on the car, even if it means it doesnt perform to its potential.
If you bump your timing up 2° and then readjust your idle, that may solve the problem.
You will want to make sure to listen closely for any pinging that may occur under load, but 34° should be pretty safe.
If that doesnt work, try another 2° and listen closely again.
Telling you to run your engine at 32° total, and not to use any vac advance sounds like the builder wants a very safe tune on the car, even if it means it doesnt perform to its potential.
Thread Starter
Instructor
Joined: Aug 2007
Posts: 131
Likes: 0
From: Madison NJ
Your engine would probably run best with 2-4 degrees more total timing than the 32 degrees that you are running right now.
If you bump your timing up 2° and then readjust your idle, that may solve the problem.
You will want to make sure to listen closely for any pinging that may occur under load, but 34° should be pretty safe.
If that doesnt work, try another 2° and listen closely again.
Telling you to run your engine at 32° total, and not to use any vac advance sounds like the builder wants a very safe tune on the car, even if it means it doesnt perform to its potential.
If you bump your timing up 2° and then readjust your idle, that may solve the problem.
You will want to make sure to listen closely for any pinging that may occur under load, but 34° should be pretty safe.
If that doesnt work, try another 2° and listen closely again.
Telling you to run your engine at 32° total, and not to use any vac advance sounds like the builder wants a very safe tune on the car, even if it means it doesnt perform to its potential.
If at idel I am at 10 degrees and at full advance I'm at 32 degrees. I change my idle timing up 2 degrees to 12 degrees my total advance will go from 32 to 34 degrees and if I go to 14 at idle, total will go to 36. Is this correct.
Drifting
Joined: Aug 2005
Posts: 1,682
Likes: 3
From: League City TX
Thats correct.