62 340 SHP Engine Problem

[Greg S.]

I am lost as to the cause of the problems I am having with this engine. It will not start now. It began having problems last weekend. It was running well until it stopped running at a stop light. It restarted and ran OK for about three miles and quit again. It restarted an ran for about 6-8 miles and began running rough with lack of power and rough idle. I limped home and left it until this weekend. Today in the garage it ran roughly for a few minutes then quit and won't restart. Seems to not have spark.

The car is NCRS correct except for 3721 AFB which is the replacement carb for the original 3269S. Carb was just rebuilt by reputable carb shop here in St Louis. Now for other details. Battery new, tests at 12.6 volts. Coil is new. New 4656 fuel pump. Gas tank was cleaned and resealed with Eastwood kit. Fuel filter is stock. Stock dual point distributor. Dwell set recently and checked at 33 when the engine ran today. Timing checked at 12 degrees. Voltage at coil checked at 12 volts and at 6.7 volts through resistor. Spark plug wires are new reproduction wires with about 10 hours run time. Distributor cap, rotor and points are in excellent shape with about 10 hours run time. Engine is in good shape mechanically with good compression. Cam is stock Duntov 098.

Engine cranks fine but no fire. I put a teaspoon or so of gas directly into the carb tried to start and still no fire. Totally non responsive.

What else can I check. I have volt and Ohmeter but am not sure how to futher diagnose this problem. I at first suspected fuel starvation but now it seems there is no spark.

Need help. It is one of those nice 70 degree days made for Corvettes and I am stuck in the garage.

[Dick W.]

Re: 62 340 SHP Engine Problem

If you have voltage the the + terminal of the coil, chances are that the coil, condenser, or points have failed. Check your dwell again as a starting point. Then the condenser, and if you have a spare GM 12V coil of any number try it. I will bet either the coil or condenser have died. RIP

[Greg S.]

Re: 62 340 SHP Engine Problem

I did try my old coil which I believe was still OK when removed. It didn't help the problem. Can a condenser cause an intermittent problem like this then fail totally? I did test the dwell this morning and it indicated 33 as the book calls for. How can you test the dwell now if the engine won't run. I did inspect the points, rotor and dist cap contacts. All looked good. Condenser is a good thought. Amazing that such a minor part could cause this kind of problem. What does it do anyway?

[Les Jacobs]

Re: 62 340 SHP Engine Problem

If there is no spark, it could be because of a problem on either the low voltage side (wiring, coil, points, condensor, wiring) or the high voltage (coil again, rotor,cables, distributor cap). On the low voltage side, power is supplied to one side of the coil (a small terminal), passes thru the coil to the other small terminal, and then is connected to the points(which are in parallel with the condensor). Start with the voltmeter on the coil, with the key on, but not cranking, you should have approximately 6-7 volts on one of the small teminals , and approximately the same on the other ((unless the points are closed or the condensor is shorted)) in which case you will have a low reading (maybe a volt or so). If you do have a lower voltage on one terminal, remove the distributor cap, and open the points by hand. The low voltage should rise. If it doesn't, either the condensor is shorted, or else the wire from the coil to the distrib is shorted to ground. (You can check all of these with your voltmeter). If the voltage does rise when you flip the points, pull the high voltage wire from the center of the distributor, and hold close to a ground point-then flip the points again. You should see a high voltage spark (and you might feel it, so wear gloves if you are concerned). If there is no spark, then either its a bad coil wire, or or else the coil (high voltage part) is bad. If you do have spark, then the only things that keep spark from getting to the spark plugs are either the distributor cap, or rotor. (Im assuming all your plug wires are good). So Id swap out both cap and rotor , and try again. Good Luck

[Duke W.]

Re: 62 340 SHP Engine Problem

Something as simple as a shorted condenser can disable the ignition system.

As far as I know the dual point uses the same condenser as the single point systems, so there is probably a new one no further than your closest auto parts store. Also check that the ground wire is firmly attached to the breaker plate and solidly connected to the dist. housing. The points make and break the ground connection from the coil and the final connection is breaker plate ground wire to distributor housing, which is grounded to the engine through the tie down clamp. If the conection is flaky it can open and close based on vibration or heat and cause intermittent ignition circuit interruption. With the points closed you should you should measure zero ohms between the coil negative terminal and ground. While checking this wiggle all the wires and the dist. breaker plate to see if any movement will break contintuity.

On vacuum advance distributors the ground wire eventually fail due to the constant movement of the breaker plate on command of the vacuum can, but even on a dual point with a fixed breaker plate the wire won't last forever. It's soldered to the breaker plate and attaches to a vacuum can hold down screw on single point distributors.

These kind of intermittent electrical problems can be maddening, especially if they are temperature related.

It takes fuel and spark to light the fire. If one is missing, the engine won't run, so it has to be one or the other. A quick and easy way to check whether it's fuel related is to squirt a shot of starting fluid (ether) into the carb air horn and crank it. If it's a spark problem it won't fire. If it's fuel, a few cylinders might fire before the ether is consumed.

Duke