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A few weeks ago I installed my MSD 6AL and GM Hei in my 68SS W/idiot lights.I had a problem w/ engine run-on.I installed a diode into the regulator and the run-on ceased.

I reset my initial timing last night to 10 w/the vacuum advance unplugged and also reset my carb adjustments.Now I have run-on again.Is this because of the timing change or should I be looking elsewhere?

I haven't changed any wiring but I installed a new intake gasket,blocked the manifold heat crossover passage, and installed new valve covers w/ only two openings- no oil cap.PCV replaced also.

EDIT-- When I left work I started the car and then after a minute or so I turned the ignition off and the car shut off.Restarted the car and drove about 4 miles to the gas station.Turned the key off and the engine quit.Got gas, drove 20 miles home and into the driveway, turned key off- engine kept running.I got out and opened the hood,covered carb until the motor stalled.Got back in the car and started it up, waited about 1min- turned key off and the engine shut off. What Gives?

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Joel
T/C#980 1968 SS396 CHEVELLE


If at first you don't succeed, skydiving is not for you.....

[This message has been edited by speedster (edited 04-03-2002).]
 

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You can have no power going to your spark plugs and still get run on. It's called desieling. you pistons get hot spots on them, or maybe even the head if it's Iron. This with high enough compression can cause run on.

how high is your idle set, RPM wise?

Did you set that timing and base idle with the vacuum advance disconnected AND plugged off?

If it might happen where it can be emberassing, leave the car in drive and shut it off. I had this problem a while back with too high of an idle setting (carb blade opening wise). I once got out at a grocery store and it starting doing it. Did it up till I got to the front door then KA-BANG! loud as ****! It shut off then damn it.


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71' 3880# with me. Big Block 402, Merlin oval heads, 10.2:1CR, TH400, 3.73 posi,
1/8th: 8.0 @ 88mph
BEST 60': 1.85 w/street tires.
BEST 1/4: 12.5 with 1.89 sixty foot (street tires)
BEST MPH: 109mph

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If it is dieseling and you can't remedy the problem by retarding the timing, you may want to install a throttle stop solenoid or a dashpot. The stop solenoid sets the idle and when you shut the engine down, it retracts closing the throttle blades, stopping the engine. The dashpot works on the same principle.

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65 Danube Blue MALIBU 4 door wagon, 350/330hp crate with 700R4, Factory air, Factory am/fm stereo.
 

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If the car isn't dieseling, check the ign enrichment wire coming from your starter to make sure it isn't touching the 12v supply post. If I remember right, it is the wire connected to the "R" post. The other thing could be the diode is too small and it is breaking down. You could get a more robust diode. I used a small bridge rectifier that has spade connectors on it and just used one leg of the rectifier (one diode between two connectors). A full wave bridge has four.

Hope this helps,

Troy.
 

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No MSD expert but Troy may have a point. MSD is now saying to use a larger diode, 400 v 1 amp.
 
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