I had an unpleasant experience last week with my 70 big block. Hadn't had the car on the road for several months. The carb has just been restored. Distributor rebuilt with new bushings and shaft, new points and plugs.

Car ran fine for the first 20 minutes or so. Once in a while I thought I detected a very brief drop out as if it were running out of gas or the key had been turned off. VERY brief, almost unnoticeable. Started to
have problems with it stalling at idle, attributed it to possibly needing a slight tweak to the idle mixture.

Stopped the car for about 15 minutes. Harder to start. Began to stall more often. Shortly afterward it stalled whenever I let off the gas.
Got so bad that it became difficult to restart. When I could I had to hold the throttle in a narrow range, too much of too little and it would die. Barely got it back home.

I put some Heet in the tank to rule out moisture. Not sure this is the fix.
The car runs warm, around 210 according to the gauge, doesn't seem outrageous.

Only two items I can think of are the carb (just restored) or ignition?

Would a coil fail this way?

Thought of the fuel pump but it seems if it were a low fuel pressure issue it should idle, low demand, but may die under load or at higher speeds.

I did not smell any gas or see any clouds of smoke which I'd expect to see if it was flooding. The problem seems to worsen after the car has been running for a while.

Any ideas? I will try to run it this weekend, let it warm up, see if the problem persists. Suspect it may.

 

The ignition module could be failing you as it heats up. If it runs good cold, take a look at that.

 

Thanks

This is a 1970 big block. No ignition module.
If it had one, it would make sense to look into it.

 

Sounds more like fuel starvation than a bad coil.

 

as old as the coil is i would replace it just to be shure.when it happens again take the air cleaner off .and check to see if you are getting gas in the carb.

 

How long since the fuel filter was changed?

 

I'd be looking to replace the condensor -the cheapest part of the system, I might add- if you have a stock distributor. Coil failures are usually a break-up under load, which makes sense since demand on the coil is greater with higher cylinder pressure.

 

Condenser is a definite possibility. Check to see if points are burned. Do you still have the resistor wire running to the coil? If not [regular wire with 12vdc going to coil], your coil was getting too much current and may have just overheated...then fried inside.

 

My coil just went bad, How did I know? there was traces of oil in the coil wire and 'tower'.

When I took mine out and left it upside down it slowly leaked out. I have had coils fail before and never saw a leak (or looked for one) but check that first. It does sound like a bad coil to me although coil failures usually happen slowly.

If you replace the coil, check how many ohms it is before you buy one, there are hundreds of different sizes and resistance.

Keep us posted and good luck.

 

On my 350 I was having some of the same issues. Ran fine at the start then after a while it was cutting out. Replaced the wires, points, plugs cap and rotor. Same issue. Worked on the carb no help. Replaced the coil problem solved. All the info I see on testing a coil on the site is a static test. Not sure how to test one under load at speed. If you know some one that has a coil swap it out and see if that fixes the issue.

 

Just one more thing to look at - check the wire from the starter solenoid to the coil.

Mine was very frayed, and as heat built up, resistence would increase and it led to the exact same issues that you describe. Someone else had the same issue, and his problem was that the wire was to close to the exhaust manifold, he simply just tied back the wire a little, and his problem cleared up. Remember, heat creates electrical resistence.

 

Oscilloscope. But not everyone has one of those laying around.

 

That's the first thing I'd think of.
The carb was recently restored and ran great for a while.
Fuel pump was replaced many years ago, virtually no run time on it.
Possible something may be failing due to age.

New paper fuel filter. Came with the carb after restoration. Looks fine.

The original resistor wire is still being used.
I replaced the coil many years ago with a new one from GM. I recall some question as to whether I had the right one. There were two part numbers listed.
I'll take a look at the points. My local Corvette shop did some work on this last year, think they were replaced.

Good idea. I recall some of the wiring was a bit toasted in that area, being close to the exhaust manifold. I have the heat shield in place. Some previous owner had discarded it.

I can get my hands on one. Never used one on a car before. What
would I look for? I'd expect to see a pulse stream on the points side.
Don't have a high voltage probe of magnetic coupler to sense the output of the coil. Maybe use the coupler from my old timing light?

At one time I began to ask around about shops who may still have one.
I've had chronic problems with intermittent skips which made me wonder about the ignition. I can't keep replacing parts, this would be round 2.

Other symptom is the cut out I hear once in a while when driving. Very brief as if the ignition had been switched off or fuel ran out. Never had a backfire, if it were ignition it seems it would have to be very brief.

Thanks everyone for your suggestions. If I find a definite fix I'll post the solution. Try to find time this weekend to work on it.

 

Mine would just quit on hard acceleration, especially when hot. Found a hairline crack from the + terminal to the center cap. Best troubleshooting technique is to replace with a known good. Know anybody with a coil that you could borrow for a few minutes?

 

...running lean? What do the plugs look like?

 

I may have found my problem. I loosened up the clamp on the coil and turned it around so I could read the part number. Delco 1115207.. Looks like it's a coil for a transistor ignition.
I have points, non transistor. I may verify tomorrow by checking the impedances though the part number appears to be a match for transistor ignition, much lower impedance.
Meant to have 2.5 to 4.5 volts when running, not 9 volts as with points.

 

BBCorv70 - I think 1115207 is for 1967...???? I found 1115263 or 1115272 were both suggested as TI (K66??Option) for 1967 - 1969 Ignition Coil. Lectric Limited says their D512R fits all without TI

How did you find the ohm , etc rating.

I have a 1969 BB w/points. I believe 11155287 is correct Delco coil (1115270 for 350 fyi), but was trying to find an alternate or more high performance appropriate coil.

Can ya'll offer guidance? My previous one was a Mallory 527 w/a Colbert 0.8 ohm external ballast

 

I am having same issues.... Running all new petronix ignition III system. Wonder if I got wrong coil...

 

Here's a link to the web site where I found my info on coils...

http://www.camaros.org/trans_ign.shtml

 

I thought about the impedances after posting. Not sure this was really a problem. Maybe it was. GM made two distinct coils, one for operation with points, the other for TI. I replaced the coil with the proper one to rule out coil problems.