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Author Topic: Run -ON  (Read 1166 times)
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shelby001
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« on: April 26, 2017, 11:32:17 AM »


 Looking for some answers to why I have run -on . Here is what I done last fall before storing the car (68 G.T 500)  replaced spark plugs BF- 32 new spark plug wires , rebuilt carb. (float level is good) but the car runs on. Could it be timing ? Car was stored so still have to find out why it runs on . What do I need to check ?

                   Thanks
 

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Paul Orr
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« Reply #1 on: April 26, 2017, 11:45:37 AM »

I have found that it is usually caused by one or more of the following:

Timing too far advanced.
Idle too high.
Running hot.

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Rodney T
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« Reply #2 on: April 26, 2017, 05:36:58 PM »

I have found that it is usually caused by one or more of the following:

Timing too far advanced.
Idle too high.
Running hot.

  Also carbon build up on the piston top or cylinder head. 

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shelby73
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« Reply #3 on: April 26, 2017, 06:32:07 PM »

Did it do it before you parked it? If not the timing didn't change sitting. Like the other fellow said could be idling too high, maybe bad fuel. Put it in gear before you cut it off till you figure it out should help cut it off. Bottom line if it did not do it when you parked it then you can point at the fuel system everything else should have stayed the same.

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BigBlock
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« Reply #4 on: April 27, 2017, 04:55:05 AM »

Have you changed the ignition system? MSD, Pertronix. You could have created a feedback path that keeps power to the coil.

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shelby001
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« Reply #5 on: April 27, 2017, 05:23:06 AM »

Did it do it before you parked it? If not the timing didn't change sitting. Like the other fellow said could be idling too high, maybe bad fuel. Put it in gear before you cut it off till you figure it out should help cut it off. Bottom line if it did not do it when you parked it then you can point at the fuel system everything else should have stayed the same.

 No this all started after changing  plugs, wires & carb rebuild , never ever had run on before & I drove it before I put it away .

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shelby001
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« Reply #6 on: April 27, 2017, 05:24:45 AM »

Have you changed the ignition system? MSD, Pertronix. You could have created a feedback path that keeps power to the coil.
 
 I have been using Pertronix on this car for years .

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Rodster-500
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« Reply #7 on: April 27, 2017, 06:03:36 AM »

How bad is the run on?  A simple case of not shutting down immediately or prolonged run on?

Speaking of run on, when this happens, is it possible for the engine to run backward?  I seen/heard some engines backfire through the carburetor after run on.

A bit unrelated but my 18hp garden tractor would always run on. The 'solution' I found was to increase the rpm's, turn off power (shutting off fuel solenoids) and the engine winds down to a total stop.  No matter how low I would decrease the rpm, it would insist on running on.

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« Reply #8 on: April 27, 2017, 08:29:11 AM »

''Run-On''   Hot carbon particles Detonating fuel in the cylinders after IGN is turned off.  An old shop trick is to spray Water into Carb  while RPM is increased.

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shelby001
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« Reply #9 on: April 27, 2017, 03:05:25 PM »

How bad is the run on?  A simple case of not shutting down immediately or prolonged run on?

Speaking of run on, when this happens, is it possible for the engine to run backward?  I seen/heard some engines backfire through the carburetor after run on.

A bit unrelated but my 18hp garden tractor would always run on. The 'solution' I found was to increase the rpm's, turn off power (shutting off fuel solenoids) and the engine winds down to a total stop.  No matter how low I would decrease the rpm, it would insist on running on.

Pro long run on to the point I put in gear & let the clutch (with foot on brake)out to kill it 

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robert campbell
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« Reply #10 on: April 27, 2017, 05:54:01 PM »

Slow down the idle speed as much as you can.  The more you can close the primary butterfly's will restrict the fuel entering the transfer slots into the carb and into the idle circuit.  My guess is after the carb rebuild you picked up a bit of idle speed on the curb idle adjustment.  Also, gas with less detonation agents could be the culprit.  Not sure how you may have treated your gas over the winter, but it also could have an effect.

If this does not help and your car is not a 4 speed we can dig deeper.  I won't bore you with what they did to the 1971 429 CJ and Boss 351 motors yet to stop run on.

Rob

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Rodster-500
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« Reply #11 on: April 27, 2017, 06:36:11 PM »

Slow down the idle speed as much as you can.  The more you can close the primary butterfly's will restrict the fuel entering the transfer slots into the carb and into the idle circuit.  My guess is after the carb rebuild you picked up a bit of idle speed on the curb idle adjustment.  Also, gas with less detonation agents could be the culprit.  Not sure how you may have treated your gas over the winter, but it also could have an effect.

If this does not help and your car is not a 4 speed we can dig deeper.  I won't bore you with what they did to the 1971 429 CJ and Boss 351 motors yet to stop run on.

Rob

Go ahead, bore me.  Wink  I'm curious.

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TOBKOB
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« Reply #12 on: April 27, 2017, 06:49:50 PM »

Quote
Slow down the idle speed as much as you can
+1...If I remember correctly it was in 1971 that Ford & Lincoln Mercury (I worked at a dealership back then) started installing the electric solenoid to completely shut the fuel off when the ignition was cut off. This was necessary to prevent dieseling as it had become a major issue.

TOB

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robert campbell
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« Reply #13 on: April 27, 2017, 09:13:26 PM »

What they did in 1971 for these two engines was to install an electric solenoid that controlled the curb idle RPM.  It was engaged when the key was in the run position and "bumped" up against a flat angled piece on the throttle plate linkage to control the curb idle speed.  When the key was turned off to shut the engine off it retracted and let the primary throttle plate or butterflies to COMPLETELY close.  This basically killed the engine with no throttle opening and eliminated "run on" when properly adjusted.  These engines were set so lean coupled with high compression and fairly aggressive cam shafts that required idle RPM's that would result in run on conditions when shut off when hot.

I spent a lot of time with one of my best friends Boss 351 back in the mid 70's.  Even with all of this we dumped the clutch to kill it most of the time.

Rob

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Rodster-500
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« Reply #14 on: April 28, 2017, 05:40:45 AM »

What they did in 1971 for these two engines was to install an electric solenoid that controlled the curb idle RPM.  It was engaged when the key was in the run position and "bumped" up against a flat angled piece on the throttle plate linkage to control the curb idle speed.  When the key was turned off to shut the engine off it retracted and let the primary throttle plate or butterflies to COMPLETELY close.  This basically killed the engine with no throttle opening and eliminated "run on" when properly adjusted.  These engines were set so lean coupled with high compression and fairly aggressive cam shafts that required idle RPM's that would result in run on conditions when shut off when hot.

I spent a lot of time with one of my best friends Boss 351 back in the mid 70's.  Even with all of this we dumped the clutch to kill it most of the time.

Rob

Interesting.  Thanks for the info.

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