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Cutting out randomly


JakeWard

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So first it's a 72 521 with a stock L16 32/36 and original distributor.

 

Driving along just fine then it'll fall on it's face like it has no spark, let out a backfire, I pull over, and it keeps idling. Soon as I try to drive away, it does the same thing over and over.

 

Anyone have something like this happen? I can't seem to replicate it on demand just inconveniently in traffic.

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So first it's a 72 521 with a stock L16 32/36 and original distributor.

 

Driving along just fine then it'll fall on it's face like it has no spark, let out a backfire, I pull over, and it keeps idling. Soon as I try to drive away, it does the same thing over and over.

 

Anyone have something like this happen? I can't seem to replicate it on demand just inconveniently in traffic.

 

Backfire out the exhaust?????????

Well you can get the same thing by turning the ignition off and then on again. The engine keeps turning pushing unburned gas and air into the exhaust. When spark is resumed all the gas in the pipe explodes. This tells me that you have an interruption of your ignition spark... could be badly worn points, any loose wire on the primary side of the coil or to the points. Start by checking every wire connection. A loose connection is hard to find, engine and driving vibration opens and closes the connection. Idle the engine and wiggle the wires.

 

Backfire out the carburetor?????????

This is almost always caused by an overly lean mixture. Remove the spark plugs and look at them. Lean mixtures will over heat the plugs and clean them, the porcelain will be very light in color or even extremely white . A proper mixture will be a tan color and a rich mixture will be very dark and even sooty black. Lean conditions can be from too small a jet or something clogging the jet.

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There is no filter on the fuel pick up pipe in the gas tank.  Crud in the tank can collect around the pick up pipe, and clog it.  When you slow down, or let the engine idle, there is not an much demand for fuel, and the crud can drift away from the pick up pipe.  A quick check of this problem is to blow air back through the fuel line toward the gas tank, and see if the problem goes away temporary.

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Backfire out the carburetor?????????

This is almost always caused by an overly lean mixture. Remove the spark plugs and look at them. Lean mixtures will over heat the plugs and clean them, the porcelain will be very light in color or even extremely white . A proper mixture will be a tan color and a rich mixture will be very dark and even sooty black. Lean conditions can be from too small a jet or something clogging the jet.

My guess

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Then look at the primary side wiring of the distributor including the points, coil and ballast resistor. Make sure the distributor is securely grounded to the engine. Are the points in good condition and gaped about 0.022"?

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I drove one of my 620s to the dump one day and it ran awesome. The next day I go to start it and nothing! It would turn over: But would not fire. It took me a while to figure it out, it was the wire inside the distributor that ran to the 2nd set of points, it had a very small nick in it and was grounding out against the inside of the distributor. I replaced it and it fired right up and ran great.

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In Cali.... it's only rain.

 

You can run your stock coil IF you keep your ballast resistor. This will only convert to a pointless ignition.

 

If you want the full effect of higher voltage you will need a one ohm 12 volt coil. Any '78 and up coil will do for this. If you try to use your points coil for this the matchbox will draw too much power through it and over heat and burn it up. A points coil is only able to handle less than 8 volts. This is why there is a ballast to drop the voltage.

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It's OK this can be adjusted back into the adjustment range.
 

 

 

Put that plate on the distributor properly so that both screws are holding it. Adjust roughly into the middle of the adjustment range.

 

Set carefully to TDC using the timing scale and notch on the crank pulley and see where the rotor is pointing on the cap above it. Where is the closest plug wire?... clockwise or counter clockwise??? Determine if you need the rotor turned clockwise or counter clockwise to get the rotor under any of the plug wires on the cap.

 

Lift the distributor out and look down, you probably will see this. (bottom picture) It's the top of the crank driven oil pump and distributor drive spindle. Take note of it's position. Unbolt the oil pump and lower it and the spindle (expect oil drips) turn and re-install it one tooth (clockwise or counter clockwise it's up to you) When the distributor is put back in it will have moved the rotor 9 degrees forward or back. Nine degrees closer to one of the plug wires. Just keep trying until the rotor is under a plug wire. Once you have it, this becomes the new No. 1 plug lead. The firing order is 1342 (counter clockwise) so if it needs changing, move all the plug wires around on the cap

 

distributortiming.jpg

 

You should now be within the adjustment range on the distributor.

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