Login  /  Register  
  Home  -  Forum  -  Classifieds  -  Photos  -  Links     

  << Previous Topic | Next Topic >>Return to Index  

what spark plugs?? Want to stop run-on at shut down

December 4 2017 at 8:49 PM
John  (Login MaSnaka)
Members

I have a new 445 build which I just started and drove for the first time two weekends ago. Edelbrock heads near 11CR. Im using the Autolite 3924's and I have run-on when I shut down the engine after a drive. Is this because I need a different spark plug? I was using these in my 390 same heads with the same problem. Or is this a timing issue? My initial is at 16 with a vacuum advance plugged. I'm not sure what causes this.

Thanks,
John

 
 Respond to this message   
AuthorReply
John
(Login MaSnaka)
Members

after some reading I realise I need to fine tune

December 4 2017, 9:31 PM 

if the problem persists then I will be back. Thanks.

 
 Respond to this message   

doug smith
(Login cjshaker)
Members

Yeah, I doubt the plugs are the issue...

December 4 2017, 9:48 PM 

But it sounds like you've discovered some of the issues that will cause this, like throttle blade opening, heat, octane rating etc, so hopefully you'll get it nailed down. 11:1 is pretty stout for a street engine, so that won't help if you're using regular fuel.

 
 Respond to this message   
Brent Lykins
(Login blykins)
Members

X2....

December 5 2017, 4:02 AM 

All of the things that Doug mentioned can contribute. I would check idle speed/throttle blade positioning first and foremost.

A 3924 is a little more plug than what I would want for 11:1 though. May try and see if a 3910 would work for you if you exhaust all other options.

 
 Respond to this message   
3pedal
(Login 3pedal)
Members

Shut it off in gear....

December 5 2017, 5:59 AM 

Also lower the idle speed


    
This message has been edited by 3pedal on Dec 5, 2017 6:01 AM


 
 Respond to this message   

john vermeersch
(Select Login johnvermeersch501)
Members

Look close at carb adjustments.........it needs

December 5 2017, 6:27 AM 

air to run or run-on....may need to get into carb for idle changes allowing you to close the throttle blades...

 
 Respond to this message   

Anonymous
(Login hs427)
Members

Re: Look close at carb adjustments.........it needs

December 5 2017, 6:30 AM 

Mine does the same thing. I have the idle screws backed all the way out. I shut it off and release the clutch in 2nd gear at the same time for now.

 
 Respond to this message   

John
(Login johnsf)
Members

Re: what spark plugs?? Want to stop run-on at shut down

December 5 2017, 6:40 AM 

I had similar problem and it turned out to be my electric puller fan. I don't know why but after I put a switch on the fan the problem stopped. Cars and engines can be crazy things.
Good luck,
J.
1956 Ford F-100 460/C6
1964 Galaxie 500/390

 
 Respond to this message   
Brent Lykins
(Login blykins)
Members

That's another good one that's often overlooked....

December 5 2017, 7:02 AM 

An electric fan can backfeed into the ignition system.

 
 Respond to this message   

Falcon67
(Login Falcon67)
Members

Fan of fans

December 5 2017, 7:45 AM 

LOL, that's always a good one. I use a relay to isolate the fans from the rest of the system but they still go "perpetual motion" for a bit on shutdown.

 
 Respond to this message   
John
(Login MaSnaka)
Members

Thanks

December 5 2017, 12:27 PM 

I have issues regarding idle which I need to get squared away first. This may be the root of my problem. If it persists I will keep after it. I know I need a good tune also regarding AF and jetting. I'm using an AED 750HP no choke carb that was tuned for my 390. Bigger displacement, higher CR, bigger intake valves may require some adjustments. I'd like to avoid having to replace it with something bigger since it is only a few years old.
Thanks,
John

 
 Respond to this message   
Anonymous
(Login jmlay)
Members

Re: what spark plugs?? Want to stop run-on at shut down

December 5 2017, 4:01 PM 

Adding a diode in the fan circuit will stop the feedback.

 
 Respond to this message   
Bones
(Login boneyard51)
Members

Run on

December 5 2017, 12:24 PM 

Ford solved this problem on their engines in the past with a electric throttle stop. It set the idle speed when the key was on , key off, throttle plates would close completely, therefore stopping “run on” These came on the engines that first received “smog tuning”. Can’t remember exact years. There are also air conditioner electric throttle stops. Of course this is just oneway to stop run on, hopefully you may tune it out. But some engines just seem to want to run on. GM, Pontiac division, iirc, turned on the A/c for a few seconds after the key was turned of to combat “run on” . Bones


    
This message has been edited by boneyard51 on Dec 5, 2017 12:43 PM


 
 Respond to this message   
Bill Ballinger
(Login 65billgal)
Members

I had to add 2 degrees more initial timing and kill the VA

December 5 2017, 5:59 PM 

when I first built my 394, I had it at 14 and 20 centrifual, and I had to kick it up to 17. At 37 it is perfect but with 4.33s it will buck and you could feel engine breaking at 65mph and up with vacuum advance. I have run it 20 and 20 for 40 and it likes that even better but it wont idle less than 1500 rpms, it does 1050 at 37 and will lay down 3 gears of both rear tire down the block.

 
 Respond to this message   

Ross
(Login Bad427stang)
Members

Order of tuning

December 6 2017, 4:26 AM 

1 - Get the timing to the max initial the engine will live with, sometimes it takes a recurve to manage total. I would expect you need at least the 16 initial you have, but if you can go to 18 it may fix it, but be sure to know your total, would hate to hurt the engine. I'd think you would want a max of 36 total with the compression you run

2 - Once timing is set, adjust idle air/fuel for best idle and lower the idle as much as it will live with (doesn't have to be excessive) A tipper here is if your ported vacuum port is alive at idle. If it is, then your throttle plates are too far open. Don't be afraid to take your time. Adjust a/f, lower idle, readjust, lower idle a little, it doesn't take a lot

3 - Make sure the engine is running cool, 195 thermostat should be OK, but if the car is overheating, you'll continue to fight it and fix that first. Sometimes the engine needs more fan, especially when it's fresh, see below.

4 - Get some miles on it and readjust the carb. A fresh motor makes heat from friction, that hurts in two ways, the heat can cause run on, but also it requires the engine to need more throttle plate opening to keep the motor running. As they loosen up often you can turn the idle setting down a bit

5 - Last as a band-aid you can run manifold vacuum to the advance and readjust the idle, it will add advance at idle and drop out when you hammer it, but I don't like doing that, I can never get the consistent idle I like, lots of guys love it though. You shouldn't need it though, as I think Bill said, 2 degrees and a good carb adjustment should get you there

In the end, your goal is to close the carburetor plates more, you can do that by adding a little timing and adjusting the carb a/f

[linked image]
---------------------------------
- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 445 cid FE, headers, RPM intake, 1000 HP series Holley, 4 speed


    
This message has been edited by Bad427stang on Dec 6, 2017 4:29 AM


 
 Respond to this message   
John
(Login MaSnaka)
Members

I have been using manifold vacuum

December 6 2017, 4:36 PM 

all along. I do notice my idle will vary when coming to a stop after cruising speed and a blip of the throttle will usually cause it to settle back down. These were the characteristics of my 390 with this same carb. Should I switch to ported vacuum or just ditch the advance altogether. Plug both ports and leave the canister on the distributor open? Also I'm not too sure how to change the dist. timing internally (Mallory Unilite). Making the adjustment at initial by adding 2 degrees will also add that to my total. Forgive me for asking a stupid question but do I check this with a timing light and raise the RPM's to find total? And at what RPM should I see it? Thanks for your help.

John

 
 Respond to this message   

Ross
(Login Bad427stang)
Members

Well

December 7 2017, 4:27 AM 

I wouldn't change too many things at once

The Mallory distributor uses a measurement tool and you can set total by adjusting a stop plate, it's very easy.

And yes, you measure total with a light by slowly revving the engine until you are sure it stops advancing. If it is a stock Unilite, it is likely going to advance until about 3000 rpm, but go a little higher than where you see it stop so you are sure.

So the 2 degrees, should help, setting total should keep you safe, idle it as low as you can and have the carb adjusted right, then get a few miles on it.

Unhooked advance won't help you at this point
[linked image]
---------------------------------
- 70 Fastback Mustang, 489 cid FE, Victor, SEFI, TKO-600 5 speed, 4.11 9 inch.
- 71 F100 shortbed 4x4, 445 cid FE, headers, RPM intake, 1000 HP series Holley, 4 speed

 
 Respond to this message   
john
(Login MaSnaka)
Members

I had a chance to check my timing

December 9 2017, 8:24 PM 

with manifold vacuum I had an initial reading of 36 and at 2800rpm and up it would go up slightly possibly to 40. There are no indicators on the balancer past 30BTDC. So all totals are a guesstimate.

with port vacuum initial is at 16 and at 2800rpm and up it would be at total 36.

With vac advance plugged initial is 16 and 2800rpm and up it would be at total 36.

I have been running with manifold vac advance without paying much attention to the timing. Maybe my new motor has a stronger manifold vac than my old one.

I have not had a chance to fool with the idle screws yet but I did take it out for a drive and still have the run on issue.

Thanks,
John

 
 Respond to this message   

6667fan
(Login 6667fan)
Members

Lots of great tips. I would add, if there is a choke on that carb

December 7 2017, 7:28 AM 

you need to make sure your fast idle cam is not occasionally hanging up on a higher idle setting. That will be just one more way the primaries might be induced to open more than is needed and contribute to run on. JMO JB
[linked image]
Every second counts

 
 Respond to this message   
Bill Ballinger
(Login 65billgal)
Members

That is a true dream car you have! nm

December 7 2017, 8:59 AM 


 
 Respond to this message   
 
  << Previous Topic | Next Topic >>Return to Index